http://journals.iucr.org/b/journalhomepage.html Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials publishes scientific articles related to the structural science of compounds and materials in the widest sense. Knowledge of the arrangements of atoms, including their temporal variations and dependencies on temperature and pressure, is often the key to understanding physical and chemical phenomena and is crucial for the design of new materials and supramolecular devices. Acta Crystallographica Section B is the forum for the publication of such contributions. Scientific developments based on experimental studies as well as those based on theoretical approaches, including crystal-structure prediction, structure-property relations and the use of databases of crystal structures, are published. en-gb Copyright (c) 2013 International Union of Crystallography International Union of Crystallography International Union of Crystallography http://journals.iucr.org urn:issn:2052-5192 Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials publishes scientific articles related to the structural science of compounds and materials in the widest sense. Knowledge of the arrangements of atoms, including their temporal variations and dependencies on temperature and pressure, is often the key to understanding physical and chemical phenomena and is crucial for the design of new materials and supramolecular devices. Acta Crystallographica Section B is the forum for the publication of such contributions. Scientific developments based on experimental studies as well as those based on theoretical approaches, including crystal-structure prediction, structure-property relations and the use of databases of crystal structures, are published. text/html Open access article in Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials text yearly 6 2002-02-01T00:00+00:00 med@iucr.org Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials Copyright (c) 2013 International Union of Crystallography urn:issn:2052-5192 http://journals.iucr.org/logos/rss10b.gif http://journals.iucr.org/b/journalhomepage.html Still image http://scripts.iucr.org/cgi-bin/paper?gp9054 Equations (13)–(18) in the paper by Touaa & Sekkal [(2012), Acta Cryst. B68, 378–388] are corrected. Copyright (c) 2013 International Union of Crystallography urn:issn:2052-5192 Touaa, Z. Sekkal, N. 2013-06-01 doi:10.1107/S2052519213009068 International Union of Crystallography Corrigendum to the data published in the article by Touaa & Sekkal [(2012), Acta Cryst. B68, 378–388]. en GROWTH AXES; SYMMETRY; SUPERLATTICE; QUANTUM WELL; ELECTRONIC STRUCTURE Equations (13)–(18) in the paper by Touaa & Sekkal [(2012), Acta Cryst. B68, 378–388] are corrected. text/html Crystallographic input data for (001), (110) and (111)-oriented superlattices. Corrigendum text 3 69 2013-06-01 Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials Copyright (c) 2013 International Union of Crystallography 2052-5192 addenda and errata med@iucr.org 2052-5206 http://scripts.iucr.org/cgi-bin/paper?so5065 Atomistic modelling techniques and Rietveld refinement of X-ray powder diffraction data are widely used but often result in crystal structures that are not realistic, presumably because the authors neglect to check the crystal-chemical plausibility of their structure. The purpose of this paper is to reinforce the importance and utility of proper crystal-chemical and geometrical reasoning in structural studies. It is achieved by using such reasoning to generate new yet fundamental information about layered double hydroxides (LDH), a large, much-studied family of compounds. LDH phases are derived from layered single hydroxides by the substitution of a fraction (x) of the divalent cations by trivalent. Equations are derived that enable calculation of x from the a parameter of the unit cell and vice versa, which can be expected to be of widespread utility as a sanity test for extant and future structure determinations and computer simulation studies. The phase at x = 0 is shown to be an α form of divalent metal hydroxide rather than the β polymorph. Crystal-chemically sensible model structures are provided for β-Zn(OH)2 and Ni- and Mg-based carbonate LDH phases that have any trivalent cation and any value of x, including x = 0 [i.e. for α-M(OH)2·mH2O phases]. http://creativecommons.org/licenses/by/2.0/uk urn:issn:0108-7681 Richardson, I.G. 2013-04-01 doi:10.1107/S0108768113003765 International Union of Crystallography The importance and utility of proper crystal-chemical and geometrical reasoning in structural studies is demonstrated through the consideration of layered single and double hydroxides. New yet fundamental information is provided and it is evident that the crystal chemistry of the double hydroxide phases is much more straightforward than is apparent from the literature. en ATOMISTIC MODELLING TECHNIQUES; X-RAY POWDER DIFFRACTION; LAYERED DOUBLE HYDROXIDES Atomistic modelling techniques and Rietveld refinement of X-ray powder diffraction data are widely used but often result in crystal structures that are not realistic, presumably because the authors neglect to check the crystal-chemical plausibility of their structure. The purpose of this paper is to reinforce the importance and utility of proper crystal-chemical and geometrical reasoning in structural studies. It is achieved by using such reasoning to generate new yet fundamental information about layered double hydroxides (LDH), a large, much-studied family of compounds. LDH phases are derived from layered single hydroxides by the substitution of a fraction (x) of the divalent cations by trivalent. Equations are derived that enable calculation of x from the a parameter of the unit cell and vice versa, which can be expected to be of widespread utility as a sanity test for extant and future structure determinations and computer simulation studies. The phase at x = 0 is shown to be an α form of divalent metal hydroxide rather than the β polymorph. Crystal-chemically sensible model structures are provided for β-Zn(OH)2 and Ni- and Mg-based carbonate LDH phases that have any trivalent cation and any value of x, including x = 0 [i.e. for α-M(OH)2·mH2O phases]. text/html The importance of proper crystal-chemical and geometrical reasoning demonstrated using layered single and double hydroxides text 2 69 2013-04-01 Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials http://creativecommons.org/licenses/by/2.0/uk 0108-7681 research papers med@iucr.org 1600-5740 http://scripts.iucr.org/cgi-bin/paper?sn5118 Invarioms are aspherical atomic scattering factors that enable structure refinement of more accurate and more precise geometries than refinements with the conventional independent atom model (IAM). The use of single-crystal X-ray diffraction data of a resolution better than sin θ/λ = 0.6 Å−1 (or d = 0.83 Å) is recommended. The invariom scattering-factor database contains transferable pseudoatom parameters of the Hansen–Coppens multipole model and associated local atomic coordinate systems. Parameters were derived from geometry optimizations of suitable model compounds, whose IUPAC names are also contained in the database. Correct scattering-factor assignment and orientation reproduces molecular electron density to a good approximation. Molecular properties can hence be derived directly from the electron-density model. Coverage of chemical environments in the invariom database has been extended from the original amino acids, proteins and nucleic acid structures to many other environments encountered in organic chemistry. With over 2750 entries it now covers a wide sample of general organic chemistry involving the elements H, C, N and O, and to a lesser extent F, Si, S, P and Cl. With respect to the earlier version of the database, the main modification concerns scattering-factor notation. Modifications improve ease of use and success rates of automatic geometry-based scattering-factor assignment, especially in condensed hetero-aromatic ring systems, making the approach well suited to replace the IAM for structures of organic molecules. Copyright (c) 2013 International Union of Crystallography urn:issn:0108-7681 Dittrich, B. Hübschle, C.B. Pröpper, K. Dietrich, F. Stolper, T. Holstein, J. . 2013-04-01 doi:10.1107/S0108768113002280 International Union of Crystallography The use of aspherical atomic scattering factors in the structure refinements of organic molecular crystals is reviewed. Aspherical atomic scattering factors within the invariom database are presented as an alternative to standard atomic scattering factors in structure refinements. en GENERALIZED INVARIOM DATABASE; ASPHERICAL ATOMIC SCATTERING FACTORS; SCATTERING-FACTOR ASSIGNMENT Invarioms are aspherical atomic scattering factors that enable structure refinement of more accurate and more precise geometries than refinements with the conventional independent atom model (IAM). The use of single-crystal X-ray diffraction data of a resolution better than sin θ/λ = 0.6 Å−1 (or d = 0.83 Å) is recommended. The invariom scattering-factor database contains transferable pseudoatom parameters of the Hansen–Coppens multipole model and associated local atomic coordinate systems. Parameters were derived from geometry optimizations of suitable model compounds, whose IUPAC names are also contained in the database. Correct scattering-factor assignment and orientation reproduces molecular electron density to a good approximation. Molecular properties can hence be derived directly from the electron-density model. Coverage of chemical environments in the invariom database has been extended from the original amino acids, proteins and nucleic acid structures to many other environments encountered in organic chemistry. With over 2750 entries it now covers a wide sample of general organic chemistry involving the elements H, C, N and O, and to a lesser extent F, Si, S, P and Cl. With respect to the earlier version of the database, the main modification concerns scattering-factor notation. Modifications improve ease of use and success rates of automatic geometry-based scattering-factor assignment, especially in condensed hetero-aromatic ring systems, making the approach well suited to replace the IAM for structures of organic molecules. text/html The generalized invariom database (GID) text 69 2 Copyright (c) 2013 International Union of Crystallography Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials 2013-04-01 91 lead articles 0108-7681 med@iucr.org 104 1600-5740 http://scripts.iucr.org/cgi-bin/paper?sn5119 The charge-flipping algorithm (CFA) is a member of the diverse family of dual-space iterative phasing algorithms. These algorithms use alternating modifications in direct and reciprocal space to find a solution to the phase problem. The current state-of-the-art CFA is reviewed and it is put in the context of related dual-space algorithms with relevance for crystallography. The CFA has found applications in many crystallographic problems. The principal applications in various fields are described with sections devoted to routine structure solution, the solution of complex structures from powder diffraction data, the solution of incommensurately modulated crystals and quasicrystals, macromolecular crystallography and single-particle imaging. Copyright (c) 2013 International Union of Crystallography urn:issn:0108-7681 Palatinus, L. 2013-02-01 doi:10.1107/S0108768112051361 International Union of Crystallography The state-of-the-art charge-flipping algorithm is summarized, and its applications to various crystallographic problems connected with structure solution are reviewed. en CHARGE-FLIPPING ALGORITHM; DUAL-SPACE METHODS; STRUCTURE SOLUTION The charge-flipping algorithm (CFA) is a member of the diverse family of dual-space iterative phasing algorithms. These algorithms use alternating modifications in direct and reciprocal space to find a solution to the phase problem. The current state-of-the-art CFA is reviewed and it is put in the context of related dual-space algorithms with relevance for crystallography. The CFA has found applications in many crystallographic problems. The principal applications in various fields are described with sections devoted to routine structure solution, the solution of complex structures from powder diffraction data, the solution of incommensurately modulated crystals and quasicrystals, macromolecular crystallography and single-particle imaging. text/html The charge-flipping algorithm in crystallography text 1 69 2013-02-01 Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials Copyright (c) 2013 International Union of Crystallography 0108-7681 lead articles 1 med@iucr.org 16 1600-5740 http://scripts.iucr.org/cgi-bin/paper?gp9038 Tables 2 and 3 in the paper by Tumanov et al. [(2010), Acta Cryst. B66, 458–471] are corrected. Copyright (c) 2012 International Union of Crystallography urn:issn:0108-7681 Tumanov, N.A. Boldyreva, E.V. Kolesov, B.A. Kurnosov, A.V. Quesada Cabrera, R. 2012-08-01 doi:10.1107/S010876811203193X International Union of Crystallography Corrigendum to the data published in the article by Tumanov et al. [(2010), Acta Cryst. B66, 458–471]. en POLYMORPHISM; AMINO ACIDS; PRESSURE; PHASE TRANSITIONS Tables 2 and 3 in the paper by Tumanov et al. [(2010), Acta Cryst. B66, 458–471] are corrected. text/html Pressure-induced phase transitions in l-alanine, revisited. Corrigendum text 68 4 Copyright (c) 2012 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2012-08-01 465 addenda and errata 0108-7681 med@iucr.org 465 1600-5740 http://scripts.iucr.org/cgi-bin/paper?pf0099 Copyright (c) 2012 International Union of Crystallography urn:issn:0108-7681 Paufler, P. 2012-06-01 doi:10.1107/S0108768112018551 International Union of Crystallography en BOOK RECEIVED text/html Symmetriebeziehungen zwischen verwandten Kristallstrukturen. Anwendungen der kristallographischen Gruppentheorie in der Kristallchemie unter Verwendung von Textvorlagen von Hans Wondratschek und Hartmut Bärnighausen. Von Ulrich Müller. Pp. 368. Wiesbaden: Vieweg + Teubner Verlag, 2012. Price (paperback) EUR 49.95. ISBN: 978-3-8348-1799-0. text 3 68 2012-06-01 Acta Crystallographica Section B: Structural Science Copyright (c) 2012 International Union of Crystallography 0108-7681 books received 321 med@iucr.org 321 1600-5740 http://scripts.iucr.org/cgi-bin/paper?sn5112 Evolutionary crystal structure prediction proved to be a powerful approach for studying a wide range of materials. Here we present a specifically designed algorithm for the prediction of the structure of complex crystals consisting of well defined molecular units. The main feature of this new approach is that each unit is treated as a whole body, which drastically reduces the search space and improves the efficiency, but necessitates the introduction of new variation operators described here. To increase the diversity of the population of structures, the initial population and part (∼ 20%) of the new generations are produced using space-group symmetry combined with random cell parameters, and random positions and orientations of molecular units. We illustrate the efficiency and reliability of this approach by a number of tests (ice, ammonia, carbon dioxide, methane, benzene, glycine and butane-1,4-diammonium dibromide). This approach easily predicts the crystal structure of methane A containing 21 methane molecules (105 atoms) per unit cell. We demonstrate that this new approach also has a high potential for the study of complex inorganic crystals as shown on examples of a complex hydrogen storage material Mg(BH4)2 and elemental boron. Copyright (c) 2012 International Union of Crystallography urn:issn:0108-7681 Zhu, Q. Oganov, A.R. Glass, C.W. Stokes, H.T. 2012-06-01 doi:10.1107/S0108768112017466 International Union of Crystallography A specially designed algorithm to predict the structure of complex crystals consisting of well defined molecular units is presented. en USPEX; COMPLEX IONS; CLUSTERS; GLOBAL OPTIMIZATION; DENSITY FUNCTIONAL THEORY; DISPERSION FORCES Evolutionary crystal structure prediction proved to be a powerful approach for studying a wide range of materials. Here we present a specifically designed algorithm for the prediction of the structure of complex crystals consisting of well defined molecular units. The main feature of this new approach is that each unit is treated as a whole body, which drastically reduces the search space and improves the efficiency, but necessitates the introduction of new variation operators described here. To increase the diversity of the population of structures, the initial population and part (∼ 20%) of the new generations are produced using space-group symmetry combined with random cell parameters, and random positions and orientations of molecular units. We illustrate the efficiency and reliability of this approach by a number of tests (ice, ammonia, carbon dioxide, methane, benzene, glycine and butane-1,4-diammonium dibromide). This approach easily predicts the crystal structure of methane A containing 21 methane molecules (105 atoms) per unit cell. We demonstrate that this new approach also has a high potential for the study of complex inorganic crystals as shown on examples of a complex hydrogen storage material Mg(BH4)2 and elemental boron. text/html Constrained evolutionary algorithm for structure prediction of molecular crystals: methodology and applications text 3 68 2012-06-01 Acta Crystallographica Section B: Structural Science Copyright (c) 2012 International Union of Crystallography 0108-7681 feature articles 215 med@iucr.org 226 1600-5740 http://scripts.iucr.org/cgi-bin/paper?sn9106 The correspondence author in the paper by Schmidt et al. [(2011), Acta Cryst. B67, 467–475] is corrected. Copyright (c) 2012 International Union of Crystallography urn:issn:0108-7681 Schmidt, H. Paschke, I. Freyer, D. Voigt, W. 2012-02-01 doi:10.1107/S0108768111051639 International Union of Crystallography Corrigendum to the article by Schmidt et al. [Acta Cryst. (2011). B67, 467–475]. en BASSANITE; CALCIUM SULFATE SUBHYDRATE; SINGLE-CRYSTAL DIFFRACTION; POWDER DIFFRACTION; PHASE TRANSITION; HIGH AIR HUMIDITY; GYPSUM The correspondence author in the paper by Schmidt et al. [(2011), Acta Cryst. B67, 467–475] is corrected. text/html Water channel structure of bassanite at high air humidity: crystal structure of CaSO4·0.625H2O. Corrigendum text 68 1 Copyright (c) 2012 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2012-02-01 addenda and errata 0108-7681 med@iucr.org 1600-5740 http://scripts.iucr.org/cgi-bin/paper?sn5109 In a previous paper we reported the lattice constants and thermal expansion of normal and deuterated ice Ih [Röttger et al. (1994). Acta Cryst. B50, 644–648]. Synchrotron X-ray powder diffraction data were used to obtain the lattice constants and unit-cell volumes of H2O and D2O ice Ih in the temperature range 15–265 K. A polynomial expression was given for the unit-cell volumes. It turns out that the coefficients quoted have an insufficient number of digits to faithfully reproduce the volume cell data. Here we provide a table with more significant digits. Moreover, we also provide the coefficients of a polynomial fit to the previously published a and c lattice constants of normal and deuterated ice Ih for the same temperature range. Copyright (c) 2012 International Union of Crystallography urn:issn:0108-7681 Röttger, K. Endriss, A. Ihringer, J. Doyle, S. Kuhs, W.F. 2012-02-01 doi:10.1107/S0108768111046908 International Union of Crystallography An addendum to the article by Röttger et al. [Acta Cryst. (1994). B50, 644–648]. en ICE IH; LATTICE CONSTANTS; THERMAL EXPANSION In a previous paper we reported the lattice constants and thermal expansion of normal and deuterated ice Ih [Röttger et al. (1994). Acta Cryst. B50, 644–648]. Synchrotron X-ray powder diffraction data were used to obtain the lattice constants and unit-cell volumes of H2O and D2O ice Ih in the temperature range 15–265 K. A polynomial expression was given for the unit-cell volumes. It turns out that the coefficients quoted have an insufficient number of digits to faithfully reproduce the volume cell data. Here we provide a table with more significant digits. Moreover, we also provide the coefficients of a polynomial fit to the previously published a and c lattice constants of normal and deuterated ice Ih for the same temperature range. text/html Lattice constants and thermal expansion of H2O and D2O Ice Ih between 10 and 265 K. Addendum text 68 1 Copyright (c) 2012 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2012-02-01 addenda and errata 0108-7681 med@iucr.org 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bk5106 Following on from the success of the previous crystal structure prediction blind tests (CSP1999, CSP2001, CSP2004 and CSP2007), a fifth such collaborative project (CSP2010) was organized at the Cambridge Crystallographic Data Centre. A range of methodologies was used by the participating groups in order to evaluate the ability of the current computational methods to predict the crystal structures of the six organic molecules chosen as targets for this blind test. The first four targets, two rigid molecules, one semi-flexible molecule and a 1:1 salt, matched the criteria for the targets from CSP2007, while the last two targets belonged to two new challenging categories – a larger, much more flexible molecule and a hydrate with more than one polymorph. Each group submitted three predictions for each target it attempted. There was at least one successful prediction for each target, and two groups were able to successfully predict the structure of the large flexible molecule as their first place submission. The results show that while not as many groups successfully predicted the structures of the three smallest molecules as in CSP2007, there is now evidence that methodologies such as dispersion-corrected density functional theory (DFT-D) are able to reliably do so. The results also highlight the many challenges posed by more complex systems and show that there are still issues to be overcome. http://creativecommons.org/licenses/by/2.0/uk urn:issn:0108-7681 Bardwell, D.A. Adjiman, C.S. Arnautova, Y.A. Bartashevich, E. Boerrigter, S.X.M. Braun, D.E. Cruz-Cabeza, A.J. Day, G.M. Della Valle, R.G. Desiraju, G.R. van Eijck, B.P. Facelli, J.C. Ferraro, M.B. Grillo, D. Habgood, M. Hofmann, D.W.M. Hofmann, F. Jose, K.V.J. Karamertzanis, P.G. Kazantsev, A.V. Kendrick, J. Kuleshova, L.N. Leusen, F.J.J. Maleev, A.V. Misquitta, A.J. Mohamed, S. Needs, R.J. Neumann, M.A. Nikylov, D. Orendt, A.M. Pal, R. Pantelides, C.C. Pickard, C.J. Price, L.S. Price, S.L. Scheraga, H.A. van de Streek, J. Thakur, T.S. Tiwari, S. Venuti, E. Zhitkov, I.K. 2011-12-01 doi:10.1107/S0108768111042868 International Union of Crystallography The results of the fifth blind test of crystal structure prediction, which show important success with more challenging large and flexible molecules, are presented and discussed. en PREDICTION; BLIND TEST; POLYMORPH; CRYSTAL STRUCTURE PREDICTION Following on from the success of the previous crystal structure prediction blind tests (CSP1999, CSP2001, CSP2004 and CSP2007), a fifth such collaborative project (CSP2010) was organized at the Cambridge Crystallographic Data Centre. A range of methodologies was used by the participating groups in order to evaluate the ability of the current computational methods to predict the crystal structures of the six organic molecules chosen as targets for this blind test. The first four targets, two rigid molecules, one semi-flexible molecule and a 1:1 salt, matched the criteria for the targets from CSP2007, while the last two targets belonged to two new challenging categories – a larger, much more flexible molecule and a hydrate with more than one polymorph. Each group submitted three predictions for each target it attempted. There was at least one successful prediction for each target, and two groups were able to successfully predict the structure of the large flexible molecule as their first place submission. The results show that while not as many groups successfully predicted the structures of the three smallest molecules as in CSP2007, there is now evidence that methodologies such as dispersion-corrected density functional theory (DFT-D) are able to reliably do so. The results also highlight the many challenges posed by more complex systems and show that there are still issues to be overcome. text/html Towards crystal structure prediction of complex organic compounds – a report on the fifth blind test text 67 6 http://creativecommons.org/licenses/by/2.0/uk Acta Crystallographica Section B: Structural Science 2011-12-01 535 research papers 0108-7681 med@iucr.org 551 1600-5740 http://scripts.iucr.org/cgi-bin/paper?sn5108 Single crystals of Ca4Fe2Mn0.5Ti0.5O9 have been synthesized using a flux method. The structural characterization using single-crystal X-ray diffraction revealed the space group Amma and unit-cell dimensions of a = 5.3510 (6), b = 26.669 (3), c = 5.4914 (6) Å. The structure is isotypic with Sr3NdFe3O9 [Barrier et al. (2005). Chem. Mater. 17, 6619–6623] and exhibits separated brownmillerite-type layers. One-dimensional diffuse scattering shows that the unit cell is doubled along c by alternating the intra-layer order of tetrahedral chains, causing stacking faults along the b direction. A computer simulation was performed, proving that the observed intensity variations along the diffuse scattering rods originates from two different local structures depending on the configuration of the tetrahedral chains. Selected-area electron diffraction experiments exhibit well ordered regions characterized by satellite reflections corresponding to two different superstructures. Both superstructures can be described using the superspace group A21/m(0βγ)0s, with γ = 0.5 and β ≃ 0.27 or β = 0. http://creativecommons.org/licenses/by/2.0/uk urn:issn:0108-7681 Krüger, H. Stöber, S. Welberry, T. Withers, R. Fitz Gerald, J. 2011-12-01 doi:10.1107/S0108768111042005 International Union of Crystallography Stacking faults in Ca4Fe2Mn0.5Ti0.5O9 have been examined using X-ray diffraction and high-resolution transmission electron microscopy. Electron diffraction revealed two superstructures with ordered stacking sequences. en LAYERED BROWNMILLERITE; DIFFUSE SCATTERING; STACKING FAULTS; MODULATED STRUCTURE Single crystals of Ca4Fe2Mn0.5Ti0.5O9 have been synthesized using a flux method. The structural characterization using single-crystal X-ray diffraction revealed the space group Amma and unit-cell dimensions of a = 5.3510 (6), b = 26.669 (3), c = 5.4914 (6) Å. The structure is isotypic with Sr3NdFe3O9 [Barrier et al. (2005). Chem. Mater. 17, 6619–6623] and exhibits separated brownmillerite-type layers. One-dimensional diffuse scattering shows that the unit cell is doubled along c by alternating the intra-layer order of tetrahedral chains, causing stacking faults along the b direction. A computer simulation was performed, proving that the observed intensity variations along the diffuse scattering rods originates from two different local structures depending on the configuration of the tetrahedral chains. Selected-area electron diffraction experiments exhibit well ordered regions characterized by satellite reflections corresponding to two different superstructures. Both superstructures can be described using the superspace group A21/m(0βγ)0s, with γ = 0.5 and β ≃ 0.27 or β = 0. text/html Stacking faults and superstructures in a layered brownmillerite text 67 6 http://creativecommons.org/licenses/by/2.0/uk Acta Crystallographica Section B: Structural Science 2011-12-01 476 research papers 0108-7681 med@iucr.org 485 1600-5740 http://scripts.iucr.org/cgi-bin/paper?dk5001 A simple method for preparing orthorhombic single crystals of benzene-silicalite-1 was developed. A silicalite-1 crystal was pressed with a weight of 2 g along the +c and −c crystallographic axes while the temperature was increased to 473 K. The temperature was then slowly reduced to 313 K, and these heating and cooling steps were repeated three times. After the orthorhombic single crystals adsorbed benzene, the crystal structure of the resulting benzene-silicalite-1 was determined. There were two kinds of benzene molecules in the asymmetric unit. One was located at the intersection of the straight channels and the sinusoidal channels with the benzene ring parallel to the ac plane. The other benzene was located in the middle of the straight channel. http://creativecommons.org/licenses/by/2.0/uk urn:issn:0108-7681 Kamiya, N. Iwama, W. Kudo, T. Nasuno, T. Fujiyama, S. Nishi, K. Yokomori, Y. 2011-12-01 doi:10.1107/S0108768111038560 International Union of Crystallography An orthorhombic benzene-silicalite-1 single crystal was obtained from a monoclinic twin crystal, and the structure was determined by a single-crystal method for the first time. en ZSM-5; MFI; SILICALITE-1; BENZENE-SILICALITE-1 A simple method for preparing orthorhombic single crystals of benzene-silicalite-1 was developed. A silicalite-1 crystal was pressed with a weight of 2 g along the +c and −c crystallographic axes while the temperature was increased to 473 K. The temperature was then slowly reduced to 313 K, and these heating and cooling steps were repeated three times. After the orthorhombic single crystals adsorbed benzene, the crystal structure of the resulting benzene-silicalite-1 was determined. There were two kinds of benzene molecules in the asymmetric unit. One was located at the intersection of the straight channels and the sinusoidal channels with the benzene ring parallel to the ac plane. The other benzene was located in the middle of the straight channel. text/html Determining the structure of a benzene7.2-silicalite-1 zeolite using a single-crystal X-ray method text 6 67 2011-12-01 Acta Crystallographica Section B: Structural Science http://creativecommons.org/licenses/by/2.0/uk 0108-7681 research papers med@iucr.org 1600-5740 http://scripts.iucr.org/cgi-bin/paper?sn5103 Fundamental structural building principles are discussed for all 56 known intermetallic phases with approximately 400 or more atoms per unit cell and space-group symmetry F\bar{4}3m, Fd\bar{3}m, Fd\bar{3}, Fm\bar{3}m or Fm\bar{3}c. Despite fundamental differences in chemical composition, bonding and electronic band structure, their complex crystal structures show striking similarities indicating common building principles. We demonstrate that the structure-determining elements are flat and puckered atomic {110} layers stacked with periodicities 2p. The atoms on this set of layers, which intersect each other, form pentagon face-sharing endohedral fullerene-like clusters arranged in a face-centered cubic packing (f.c.c.). Due to their topological layer structure, all these crystal structures can be described as (p × p × p) = p3-fold superstructures of a common basic structure of the double-diamond type. The parameter p, with p = 3, 4, 7 or 11, is determined by the number of layers per repeat unit and the type of cluster packing, which in turn are controlled by chemical composition. Copyright (c) 2011 International Union of Crystallography urn:issn:0108-7681 Dshemuchadse, J. Jung, D.Y. Steurer, W. 2011-08-01 doi:10.1107/S0108768111025390 International Union of Crystallography Common fundamental structural building principles are discussed for complex intermetallics with giant unit cells and symmetries F\bar{4}3m, Fd\bar{3}m, Fd\bar{3}, Fm\bar{3}m and Fm\bar{3}c. en FACE-CENTERED CUBIC INTERMETALLICS; STRUCTURAL BUILDING PRINCIPLES Fundamental structural building principles are discussed for all 56 known intermetallic phases with approximately 400 or more atoms per unit cell and space-group symmetry F\bar{4}3m, Fd\bar{3}m, Fd\bar{3}, Fm\bar{3}m or Fm\bar{3}c. Despite fundamental differences in chemical composition, bonding and electronic band structure, their complex crystal structures show striking similarities indicating common building principles. We demonstrate that the structure-determining elements are flat and puckered atomic {110} layers stacked with periodicities 2p. The atoms on this set of layers, which intersect each other, form pentagon face-sharing endohedral fullerene-like clusters arranged in a face-centered cubic packing (f.c.c.). Due to their topological layer structure, all these crystal structures can be described as (p × p × p) = p3-fold superstructures of a common basic structure of the double-diamond type. The parameter p, with p = 3, 4, 7 or 11, is determined by the number of layers per repeat unit and the type of cluster packing, which in turn are controlled by chemical composition. text/html Structural building principles of complex face-centered cubic intermetallics text 4 67 2011-08-01 Acta Crystallographica Section B: Structural Science Copyright (c) 2011 International Union of Crystallography 0108-7681 feature articles 269 med@iucr.org 292 1600-5740 http://scripts.iucr.org/cgi-bin/paper?ps5012 An improved algorithm has been developed for assigning chemical structures to incoming entries to the Cambridge Structural Database, using only the information available in the deposited CIF. Steps in the algorithm include detection of bonds, selection of polymer unit, resolution of disorder, and assignment of bond types and formal charges. The chief difficulty is posed by the large number of metallo-organic crystal structures that must be processed, given our aspiration that assigned chemical structures should accurately reflect properties such as the oxidation states of metals and redox-active ligands, metal coordination numbers and hapticities, and the aromaticity or otherwise of metal ligands. Other complications arise from disorder, especially when it is symmetry imposed or modelled with the SQUEEZE algorithm. Each assigned structure is accompanied by an estimate of reliability and, where necessary, diagnostic information indicating probable points of error. Although the algorithm was written to aid building of the Cambridge Structural Database, it has the potential to develop into a general-purpose tool for adding chemical information to newly determined crystal structures. http://creativecommons.org/licenses/by/2.0/uk urn:issn:0108-7681 Bruno, I.J. Shields, G.P. Taylor, R. 2011-08-01 doi:10.1107/S0108768111024608 International Union of Crystallography An improved algorithm has been written for assigning chemical structures to incoming entries to the Cambridge Structural Database. en CAMBRIDGE STRUCTURAL DATABASE; STRUCTURE ASSIGNMENT; CATENA STRUCTURE; DISORDER RESOLUTION; BAYESIAN STATISTICS An improved algorithm has been developed for assigning chemical structures to incoming entries to the Cambridge Structural Database, using only the information available in the deposited CIF. Steps in the algorithm include detection of bonds, selection of polymer unit, resolution of disorder, and assignment of bond types and formal charges. The chief difficulty is posed by the large number of metallo-organic crystal structures that must be processed, given our aspiration that assigned chemical structures should accurately reflect properties such as the oxidation states of metals and redox-active ligands, metal coordination numbers and hapticities, and the aromaticity or otherwise of metal ligands. Other complications arise from disorder, especially when it is symmetry imposed or modelled with the SQUEEZE algorithm. Each assigned structure is accompanied by an estimate of reliability and, where necessary, diagnostic information indicating probable points of error. Although the algorithm was written to aid building of the Cambridge Structural Database, it has the potential to develop into a general-purpose tool for adding chemical information to newly determined crystal structures. text/html Deducing chemical structure from crystallographically determined atomic coordinates text 67 4 http://creativecommons.org/licenses/by/2.0/uk Acta Crystallographica Section B: Structural Science 2011-08-01 333 research papers 0108-7681 med@iucr.org 349 1600-5740 http://scripts.iucr.org/cgi-bin/paper?pi9008 The De (dissociation energy) values in Table 6 of the article by Zarychta et al. [(2011). Acta Cryst. B67, 250–262] are corrected. Copyright (c) 2011 International Union of Crystallography urn:issn:0108-7681 Zarychta, B. Zaleski, J. Kyzioł, J. Daszkiewicz, Z. Jelsch, C. 2011-08-01 doi:10.1107/S0108768111020374 International Union of Crystallography A correction to the article by Zarychta et al. [(2011). Acta Cryst. B67, 250–262]. en CRYSTAL STRUCTURE REFINEMENT; CHARGE DENSITY; ENERGY CALCULATIONS; INTERMOLECULAR INTERACTIONS; CORRIGENDUM The De (dissociation energy) values in Table 6 of the article by Zarychta et al. [(2011). Acta Cryst. B67, 250–262] are corrected. text/html Charge-density analysis of 1-nitroindoline: refinement quality using free R factors and restraints. Corrigendum text 4 67 2011-08-01 Acta Crystallographica Section B: Structural Science Copyright (c) 2011 International Union of Crystallography 0108-7681 addenda and errata med@iucr.org 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bp5035 A combination of structure refinements, analysis of the superspace MEM density and interpretation of difference-Fourier maps has been used to characterize the incommensurate modulation of rubidium tetrachlorozincate, Rb2ZnCl4, at a temperature of T = 196 K, close to the lock-in transition at Tlock-in = 192 K. The modulation is found to consist of a combination of displacement modulation functions, modulated atomic displacement parameters (ADPs) and modulated third-order anharmonic ADPs. Up to fifth-order Fourier coefficients could be refined against diffraction data containing up to fifth-order satellite reflections. The center-of-charge of the atomic basins of the MEM density and the displacive modulation functions of the structure model provide equivalent descriptions of the displacive modulation. Modulations of the ADPs and anharmonic ADPs are visible in the MEM density, but extracting quantitative information about these modulations appears to be difficult. In the structure refinements the modulation parameters of the ADPs form a dependent set, and ad hoc restrictions had to be introduced in the refinements. It is suggested that modulated harmonic ADPs and modulated third-order anharmonic ADPs form an intrinsic part, however small, of incommensurately modulated structures in general. Refinements of alternate models with and without parameters for modulated ADPs lead to significant differences between the parameters of the displacement modulation in these two types of models, thus showing the modulation of ADPs to be important for a correct description of the displacive modulation. The resulting functions do not provide evidence for an interpretation of the modulation by a soliton model. http://creativecommons.org/licenses/by/2.0/uk urn:issn:0108-7681 Li, L. Wölfel, A. Schönleber, A. Mondal, S. Schreurs, A.M.M. Kroon-Batenburg, L.M.J. van Smaalen, S. 2011-06-01 doi:10.1107/S0108768111013814 International Union of Crystallography The superspace maximum entropy method (MEM) density in combination with structure refinements has been used to uncover the modulation in incommensurate Rb2ZnCl4 close to the lock-in transition. Modulated atomic displacement parameters (ADPs) and modulated anharmonic ADPs are found to form an intrinsic part of the modulation. Refined values for the displacement modulation function depend on the presence or absence of modulated ADPs in the model. en APERIODIC CRYSTALS; INCOMMENSURATE MODULATED STRUCTURES; MEM DENSITY; ADPS A combination of structure refinements, analysis of the superspace MEM density and interpretation of difference-Fourier maps has been used to characterize the incommensurate modulation of rubidium tetrachlorozincate, Rb2ZnCl4, at a temperature of T = 196 K, close to the lock-in transition at Tlock-in = 192 K. The modulation is found to consist of a combination of displacement modulation functions, modulated atomic displacement parameters (ADPs) and modulated third-order anharmonic ADPs. Up to fifth-order Fourier coefficients could be refined against diffraction data containing up to fifth-order satellite reflections. The center-of-charge of the atomic basins of the MEM density and the displacive modulation functions of the structure model provide equivalent descriptions of the displacive modulation. Modulations of the ADPs and anharmonic ADPs are visible in the MEM density, but extracting quantitative information about these modulations appears to be difficult. In the structure refinements the modulation parameters of the ADPs form a dependent set, and ad hoc restrictions had to be introduced in the refinements. It is suggested that modulated harmonic ADPs and modulated third-order anharmonic ADPs form an intrinsic part, however small, of incommensurately modulated structures in general. Refinements of alternate models with and without parameters for modulated ADPs lead to significant differences between the parameters of the displacement modulation in these two types of models, thus showing the modulation of ADPs to be important for a correct description of the displacive modulation. The resulting functions do not provide evidence for an interpretation of the modulation by a soliton model. text/html Modulated anharmonic ADPs are intrinsic to aperiodic crystals: a case study on incommensurate Rb2ZnCl4 text 3 67 2011-06-01 Acta Crystallographica Section B: Structural Science http://creativecommons.org/licenses/by/2.0/uk 0108-7681 research papers 205 med@iucr.org 217 1600-5740 http://scripts.iucr.org/cgi-bin/paper?so5041 This paper describes the validation of a dispersion-corrected density functional theory (d-DFT) method for the purpose of assessing the correctness of experimental organic crystal structures and enhancing the information content of purely experimental data. 241 experimental organic crystal structures from the August 2008 issue of Acta Cryst. Section E were energy-minimized in full, including unit-cell parameters. The differences between the experimental and the minimized crystal structures were subjected to statistical analysis. The r.m.s. Cartesian displacement excluding H atoms upon energy minimization with flexible unit-cell parameters is selected as a pertinent indicator of the correctness of a crystal structure. All 241 experimental crystal structures are reproduced very well: the average r.m.s. Cartesian displacement for the 241 crystal structures, including 16 disordered structures, is only 0.095 Å (0.084 Å for the 225 ordered structures). R.m.s. Cartesian displacements above 0.25 Å either indicate incorrect experimental crystal structures or reveal interesting structural features such as exceptionally large temperature effects, incorrectly modelled disorder or symmetry breaking H atoms. After validation, the method is applied to nine examples that are known to be ambiguous or subtly incorrect. http://creativecommons.org/licenses/by/2.0/uk urn:issn:0108-7681 van de Streek, J. Neumann, M.A. 2010-10-01 doi:10.1107/S0108768110031873 International Union of Crystallography The accuracy of a dispersion-corrected density functional theory method is validated against 241 experimental organic crystal structures from Acta Cryst. Section E. en DISPERSION-CORRECTED DENSITY FUNCTIONAL THEORY; ORGANIC STRUCTURES This paper describes the validation of a dispersion-corrected density functional theory (d-DFT) method for the purpose of assessing the correctness of experimental organic crystal structures and enhancing the information content of purely experimental data. 241 experimental organic crystal structures from the August 2008 issue of Acta Cryst. Section E were energy-minimized in full, including unit-cell parameters. The differences between the experimental and the minimized crystal structures were subjected to statistical analysis. The r.m.s. Cartesian displacement excluding H atoms upon energy minimization with flexible unit-cell parameters is selected as a pertinent indicator of the correctness of a crystal structure. All 241 experimental crystal structures are reproduced very well: the average r.m.s. Cartesian displacement for the 241 crystal structures, including 16 disordered structures, is only 0.095 Å (0.084 Å for the 225 ordered structures). R.m.s. Cartesian displacements above 0.25 Å either indicate incorrect experimental crystal structures or reveal interesting structural features such as exceptionally large temperature effects, incorrectly modelled disorder or symmetry breaking H atoms. After validation, the method is applied to nine examples that are known to be ambiguous or subtly incorrect. text/html Validation of experimental molecular crystal structures with dispersion-corrected density functional theory calculations text 66 5 http://creativecommons.org/licenses/by/2.0/uk Acta Crystallographica Section B: Structural Science 2010-10-01 544 research papers 0108-7681 med@iucr.org 558 1600-5740 http://scripts.iucr.org/cgi-bin/paper?wh5010 Theoretical calculations of the electron-localization function show that, at the volumes of the two CaO phases (rocksalt and CsCl type), the parent Ca structures (fcc: face-centred cubic and sc: simple cubic, respectively) exhibit charge concentration zones which coincide with the positions occupied by the O atoms in their oxides. Similar features, also observed for the pairs Ca/CaF2 and BaSn/BaSnO3, are supported by recent high-pressure experiments as well as electron-localization function (ELF) calculations, carried out on elemental K. At very high pressures, the elemental K adopts the hP4 structure, topologically identical to that of the K atoms in high-pressure K2S and high-temperature α-K2SO4. Moreover, the ELF for the hP4 structure shows charge concentration (∼ 2 electrons) at the sites occupied by the S atoms in the high-pressure K2S phase. All these features confirm the oxidation/high-pressure equivalence as well as the prediction of how cation arrays should be metastable phases of the parent metals. For the first time to our knowledge, the structure type, dimension and topology of several oxides and fluorides (CaO, CaF2 and BaSnO3) are explained in univocal physical terms. http://creativecommons.org/licenses/by/2.0/uk urn:issn:0108-7681 Vegas, Á. Mattesini, M. 2010-06-01 doi:10.1107/S0108768110013200 International Union of Crystallography Theoretical calculations of the electron-localization function show that, at the volumes of the two CaO phases (rocksalt and CsCl type), the parent Ca structures (fcc: face-centred cubic; sc: simple cubic) exhibit charge-concentration zones which coincide with the positions occupied by the O atoms in their oxides. For the first time, the structure type, dimension and topology of CaO and BaSnO3 are explained in univocal physical terms. en ELECTRON LOCALIZATION; HIGH-PRESSURE EXPERIMENTS Theoretical calculations of the electron-localization function show that, at the volumes of the two CaO phases (rocksalt and CsCl type), the parent Ca structures (fcc: face-centred cubic and sc: simple cubic, respectively) exhibit charge concentration zones which coincide with the positions occupied by the O atoms in their oxides. Similar features, also observed for the pairs Ca/CaF2 and BaSn/BaSnO3, are supported by recent high-pressure experiments as well as electron-localization function (ELF) calculations, carried out on elemental K. At very high pressures, the elemental K adopts the hP4 structure, topologically identical to that of the K atoms in high-pressure K2S and high-temperature α-K2SO4. Moreover, the ELF for the hP4 structure shows charge concentration (∼ 2 electrons) at the sites occupied by the S atoms in the high-pressure K2S phase. All these features confirm the oxidation/high-pressure equivalence as well as the prediction of how cation arrays should be metastable phases of the parent metals. For the first time to our knowledge, the structure type, dimension and topology of several oxides and fluorides (CaO, CaF2 and BaSnO3) are explained in univocal physical terms. text/html Towards a generalized vision of oxides: disclosing the role of cations and anions in determining unit-cell dimensions text 66 3 http://creativecommons.org/licenses/by/2.0/uk Acta Crystallographica Section B: Structural Science 2010-06-01 338 research papers 0108-7681 med@iucr.org 344 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bk5091 Certain complex structures are logically regarded as intergrowths of chemically or topologically discrete modules. When the proportions of these components vary systematically a polysomatic series is created, whose construction provides a basis for understanding defects, symmetry alternation and trends in physical properties. Here, we describe the polysomatic family A5NB3NO9N + 6XNδ (2 ≤ N ≤ ∞) that is built by condensing N apatite modules (A5B3O18Xδ) in configurations to create BnO3n + 1 (1 ≤ n ≤ ∞) tetrahedral chains. Hydroxyapatite [Ca10(PO4)6(OH)2] typifies a widely studied polysome where N = 2 and the tetrahedra are isolated in A10(BO4)6X2 compounds, but N = 3 A15(B2O7)3(BO4)3X3 (ganomalite) and N = 4 A20(B2O7)6X4 (nasonite) are also known, with the X site untenanted or partially occupied as required for charge balance. The apatite modules, while topologically identical, are often compositionally or symmetrically distinct, and an infinite number of polysomes is feasible, generally with the restriction being that an A:B = 5:3 cation ratio be maintained. The end-members are the N = 2 polysome with all tetrahedra separated, and N = ∞, in which the hypothetical compound A5B3O9X contains infinite, corner-connected tetrahedral strings. The principal characteristics of a polysome are summarized using the nomenclature apatite-(A B X)-NS, where A/B/X are the most abundant species in these sites, N is the number of modules in the crystallographic repeat, and S is the symmetry symbol (usually H, T, M or A). This article examines the state-of-the-art in polysomatic apatite synthesis and crystallochemical design. It also presents X-ray and neutron powder diffraction investigations for several polysome chemical series and examines the prevalence of stacking disorder by electron microscopy. These insights into the structure-building principles of apatite polysomes will guide their development as functional materials. Copyright (c) 2010 International Union of Crystallography urn:issn:0108-7681 Baikie, T. Pramana, S.S. Ferraris, C. Huang, Y. Kendrick, E. Knight, K. Ahmad, Z. White, T.J. 2010-02-01 doi:10.1107/S0108768109053981 International Union of Crystallography The polysomatic apatite family A5NB3NO9N + 6XNδ (2 ≤ N ≤ ∞) is built by condensing N apatite modules (A5B3O18Xδ) in configurations to create BnO3n + 1 (1 ≤ n ≤ ∞) tetrahedral chains. Hydroxyapatite [Ca10(PO4)6(OH)2] typifies the N = 2 polysome, but N = 3 A15(B2O7)3(BO4)3X3 (ganomalite) and N = 4 A20(B2O7)6X4 (nasonite) are also known. en POLYSOMATIC SERIES; APATITE; POWDER DIFFRACTION Certain complex structures are logically regarded as intergrowths of chemically or topologically discrete modules. When the proportions of these components vary systematically a polysomatic series is created, whose construction provides a basis for understanding defects, symmetry alternation and trends in physical properties. Here, we describe the polysomatic family A5NB3NO9N + 6XNδ (2 ≤ N ≤ ∞) that is built by condensing N apatite modules (A5B3O18Xδ) in configurations to create BnO3n + 1 (1 ≤ n ≤ ∞) tetrahedral chains. Hydroxyapatite [Ca10(PO4)6(OH)2] typifies a widely studied polysome where N = 2 and the tetrahedra are isolated in A10(BO4)6X2 compounds, but N = 3 A15(B2O7)3(BO4)3X3 (ganomalite) and N = 4 A20(B2O7)6X4 (nasonite) are also known, with the X site untenanted or partially occupied as required for charge balance. The apatite modules, while topologically identical, are often compositionally or symmetrically distinct, and an infinite number of polysomes is feasible, generally with the restriction being that an A:B = 5:3 cation ratio be maintained. The end-members are the N = 2 polysome with all tetrahedra separated, and N = ∞, in which the hypothetical compound A5B3O9X contains infinite, corner-connected tetrahedral strings. The principal characteristics of a polysome are summarized using the nomenclature apatite-(A B X)-NS, where A/B/X are the most abundant species in these sites, N is the number of modules in the crystallographic repeat, and S is the symmetry symbol (usually H, T, M or A). This article examines the state-of-the-art in polysomatic apatite synthesis and crystallochemical design. It also presents X-ray and neutron powder diffraction investigations for several polysome chemical series and examines the prevalence of stacking disorder by electron microscopy. These insights into the structure-building principles of apatite polysomes will guide their development as functional materials. text/html Polysomatic apatites text 66 1 Copyright (c) 2010 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2010-02-01 1 feature articles 0108-7681 med@iucr.org 16 1600-5740 http://scripts.iucr.org/cgi-bin/paper?dr5024 The structure of a complicated quasicrystal approximant ∊16 was predicted from a known and related quasicrystal approximant ∊6 by the strong-reflections approach. Electron-diffraction studies show that in reciprocal space, the positions of the strongest reflections and their intensity distributions are similar for both approximants. By applying the strong-reflections approach, the structure factors of ∊16 were deduced from those of the known ∊6 structure. Owing to the different space groups of the two structures, a shift of the phase origin had to be applied in order to obtain the phases of ∊16. An electron-density map of ∊16 was calculated by inverse Fourier transformation of the structure factors of the 256 strongest reflections. Similar to that of ∊6, the predicted structure of ∊16 contains eight layers in each unit cell, stacked along the b axis. Along the b axis, ∊16 is built by banana-shaped tiles and pentagonal tiles; this structure is confirmed by high-resolution transmission electron microscopy (HRTEM). The simulated precession electron-diffraction (PED) patterns from the structure model are in good agreement with the experimental ones. ∊16 with 153 unique atoms in the unit cell is the most complicated approximant structure ever solved or predicted. http://creativecommons.org/licenses/by/2.0/uk urn:issn:0108-7681 Li, M. Sun, J. Oleynikov, P. Hovmöller, S. Zou, X. Grushko, B. 2010-02-01 doi:10.1107/S0108768109053804 International Union of Crystallography The structure of the quasicrystal approximant ∊16 was predicted by the strong-reflections approach based on the known approximant ∊6. en QUASICRYSTAL APPROXIMANT; STRONG-REFLECTIONS APPROACH; ELECTRON DIFFRACTION; INVERSE FOURIER TRANSFORMATION The structure of a complicated quasicrystal approximant ∊16 was predicted from a known and related quasicrystal approximant ∊6 by the strong-reflections approach. Electron-diffraction studies show that in reciprocal space, the positions of the strongest reflections and their intensity distributions are similar for both approximants. By applying the strong-reflections approach, the structure factors of ∊16 were deduced from those of the known ∊6 structure. Owing to the different space groups of the two structures, a shift of the phase origin had to be applied in order to obtain the phases of ∊16. An electron-density map of ∊16 was calculated by inverse Fourier transformation of the structure factors of the 256 strongest reflections. Similar to that of ∊6, the predicted structure of ∊16 contains eight layers in each unit cell, stacked along the b axis. Along the b axis, ∊16 is built by banana-shaped tiles and pentagonal tiles; this structure is confirmed by high-resolution transmission electron microscopy (HRTEM). The simulated precession electron-diffraction (PED) patterns from the structure model are in good agreement with the experimental ones. ∊16 with 153 unique atoms in the unit cell is the most complicated approximant structure ever solved or predicted. text/html A complicated quasicrystal approximant ∊16 predicted by the strong-reflections approach text 66 1 http://creativecommons.org/licenses/by/2.0/uk Acta Crystallographica Section B: Structural Science 2010-02-01 17 research papers 0108-7681 med@iucr.org 26 1600-5740 http://scripts.iucr.org/cgi-bin/paper?es0375 Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Abrahams, S.C. Hedberg, K. 2009-12-01 doi:10.1107/S0108768109047533 International Union of Crystallography en OBITUARIES text/html Clara Brink Shoemaker (1921–2009) text 65 6 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2009-12-01 788 obituaries 0108-7681 med@iucr.org 790 1600-5740 http://scripts.iucr.org/cgi-bin/paper?ck9038 In the paper by Cormary et al. [Acta Cryst. (2009), B65, 612–623] two authors were inadvertently omitted from the author list and one name was given incorrectly. Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Cormary, B. Malfant, I. Valade, L. Buron-Le Cointe, M. Toupet, L. Todorova, T. Delley, B. Schaniel, D. Mockus, N. Woike, T. Fejfarová, K. Petříček, V. Dušek, M. 2009-12-01 doi:10.1107/S0108768109044899 International Union of Crystallography Erratum to Cormary et al. (2009), Acta Cryst. B65, 612–623. en METASTABLE PHASES; PHOTOCRYSTALLOGRAPHY; DENSITY FUNCTIONAL CALCULATIONS In the paper by Cormary et al. [Acta Cryst. (2009), B65, 612–623] two authors were inadvertently omitted from the author list and one name was given incorrectly. text/html [Ru(py)4Cl(NO)](PF6)2·0.5H2O: a model system for structural determination and ab initio calculations of photo-induced linkage NO isomers. Erratum text 65 6 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2009-12-01 787 addenda and errata 0108-7681 med@iucr.org 787 1600-5740 http://scripts.iucr.org/cgi-bin/paper?pi5001 Charge densities have been determined by the Maximum Entropy Method (MEM) from the high-resolution, low-temperature (T ≃ 20 K) X-ray diffraction data of six different crystals of amino acids and peptides. A comparison of dynamic deformation densities of the MEM with static and dynamic deformation densities of multipole models shows that the MEM may lead to a better description of the electron density in hydrogen bonds in cases where the multipole model has been restricted to isotropic displacement parameters and low-order multipoles (lmax = 1) for the H atoms. Topological properties at bond critical points (BCPs) are found to depend systematically on the bond length, but with different functions for covalent C—C, C—N and C—O bonds, and for hydrogen bonds together with covalent C—H and N—H bonds. Similar dependencies are known for AIM properties derived from static multipole densities. The ratio of potential and kinetic energy densities |V(BCP)|/G(BCP) is successfully used for a classification of hydrogen bonds according to their distance d(H⋯O) between the H atom and the acceptor atom. The classification based on MEM densities coincides with the usual classification of hydrogen bonds as strong, intermediate and weak [Jeffrey (1997). An Introduction to Hydrogen Bonding. Oxford University Press]. MEM and procrystal densities lead to similar values of the densities at the BCPs of hydrogen bonds, but differences are shown to prevail, such that it is found that only the true charge density, represented by MEM densities, the multipole model or some other method can lead to the correct characterization of chemical bonding. Our results do not confirm suggestions in the literature that the promolecule density might be sufficient for a characterization of hydrogen bonds. http://creativecommons.org/licenses/by/2.0/uk urn:issn:0108-7681 Netzel, J. van Smaalen, S. 2009-10-01 doi:10.1107/S0108768109026767 International Union of Crystallography The maximum-entropy charge densities of six amino acids and peptides reveal systematic dependencies of the properties at bond critical points on bond lengths. MEM densities demonstrate that low-order multipoles (lmax = 1) and isotropic atomic displacement parameters for H atoms in the multipole model are insufficient for capturing all the features of charge densities in hydrogen bonds. en TOPOLOGICAL PROPERTIES; HYDROGEN BONDING; MAXIMUM ENTROPY METHOD; CHARGE DENSITIES; PEPTIDES; AMINO ACIDS Charge densities have been determined by the Maximum Entropy Method (MEM) from the high-resolution, low-temperature (T ≃ 20 K) X-ray diffraction data of six different crystals of amino acids and peptides. A comparison of dynamic deformation densities of the MEM with static and dynamic deformation densities of multipole models shows that the MEM may lead to a better description of the electron density in hydrogen bonds in cases where the multipole model has been restricted to isotropic displacement parameters and low-order multipoles (lmax = 1) for the H atoms. Topological properties at bond critical points (BCPs) are found to depend systematically on the bond length, but with different functions for covalent C—C, C—N and C—O bonds, and for hydrogen bonds together with covalent C—H and N—H bonds. Similar dependencies are known for AIM properties derived from static multipole densities. The ratio of potential and kinetic energy densities |V(BCP)|/G(BCP) is successfully used for a classification of hydrogen bonds according to their distance d(H⋯O) between the H atom and the acceptor atom. The classification based on MEM densities coincides with the usual classification of hydrogen bonds as strong, intermediate and weak [Jeffrey (1997). An Introduction to Hydrogen Bonding. Oxford University Press]. MEM and procrystal densities lead to similar values of the densities at the BCPs of hydrogen bonds, but differences are shown to prevail, such that it is found that only the true charge density, represented by MEM densities, the multipole model or some other method can lead to the correct characterization of chemical bonding. Our results do not confirm suggestions in the literature that the promolecule density might be sufficient for a characterization of hydrogen bonds. text/html Topological properties of hydrogen bonds and covalent bonds from charge densities obtained by the maximum entropy method (MEM) text 65 5 http://creativecommons.org/licenses/by/2.0/uk Acta Crystallographica Section B: Structural Science 2009-10-01 624 research papers 0108-7681 med@iucr.org 638 1600-5740 http://scripts.iucr.org/cgi-bin/paper?hw9003 An error in the paper by Malcherek & Schlüter (2009), Acta Cryst. B65, 334–341, is corrected. Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Malcherek, T. Schlüter, J. 2009-08-01 doi:10.1107/S0108768109020916 International Union of Crystallography A corrigendum to the paper by Malcherek & Schlüter (2009), Acta Cryst. B65, 334–341. en CLINOATACAMITE; PARATACAMITE; HERBERTSMITHITE; KAGOME ANTIFERROMAGNET An error in the paper by Malcherek & Schlüter (2009), Acta Cryst. B65, 334–341, is corrected. text/html Structures of the pseudo-trigonal polymorphs of Cu2(OH)3Cl. Corrigendum text 65 4 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2009-08-01 516 addenda and errata 0108-7681 med@iucr.org 516 1600-5740 http://scripts.iucr.org/cgi-bin/paper?pf0073 Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Müller, U. 2009-08-01 doi:10.1107/S0108768109020011 International Union of Crystallography en BOOK REVIEW text/html Molecular Clusters. A Bridge to Solid-State Chemistry. By Thomas P. Fehlner, Jean-François Halet and Jean-Yves Saillard. Pp. xii + 378. Cambridge University Press, 2007. Price £70. ISBN 978-0-521-85236-4 text 65 4 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2009-08-01 517 book reviews 0108-7681 med@iucr.org 518 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bk5084 The X-ray analysis of (6R,7aS)-6-(tert-butyl-dimethylsilanyloxy)-1-hydroxy-2-phenyl-5,6,7,7a-tetrahydropyrrolizin-3-one, C19H27NO3Si, revealed a diffraction pattern which is typical for modulated structures: strong Bragg peaks surrounded by weaker reflections which cannot be indexed with the same three reciprocal lattice vectors that are used to describe the strong peaks. For this class of crystal structures the concept of superspace has been developed which, however, for many crystallographers still constitutes a Gordian Knot. As a possible tool to cut this knot the crystal structure of the above-mentioned tetrahydropyrrolizinone derivative is presented as an illustrative example for handling and describing the modulated structure of a typical pharmaceutical (i.e. molecular) compound. Having established a working knowledge of the concepts and terminology of the superspace approach a concise and detailed description of the complete process of peak indexing, data processing, structure solution and structure interpretation is presented for the incommensurately modulated crystal structure of the above-mentioned compound. The superspace symmetry applied is P21(α0γ)0; the (incommensurate) q vector components at 100 K are α = 0.1422 (2) and γ = 0.3839 (8). Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Wagner, T. Schönleber, A. 2009-06-01 doi:10.1107/S0108768109015614 International Union of Crystallography The basic principles of handling and describing modulated structures with the superspace formalism are given in a non-mathematical way. They are illustrated using the crystal structure of (6R,7aS)-6-(tert-butyl-dimethylsilanyloxy)-1-hydroxy-2-phenyl-5,6,7,7a-tetrahydropyrrolizin-3-one, C19H27NO3Si. en MOLECULAR COMPOUND; INCOMMENSURATELY MODULATED STRUCTURE; SUPERSPACE; TEACHING The X-ray analysis of (6R,7aS)-6-(tert-butyl-dimethylsilanyloxy)-1-hydroxy-2-phenyl-5,6,7,7a-tetrahydropyrrolizin-3-one, C19H27NO3Si, revealed a diffraction pattern which is typical for modulated structures: strong Bragg peaks surrounded by weaker reflections which cannot be indexed with the same three reciprocal lattice vectors that are used to describe the strong peaks. For this class of crystal structures the concept of superspace has been developed which, however, for many crystallographers still constitutes a Gordian Knot. As a possible tool to cut this knot the crystal structure of the above-mentioned tetrahydropyrrolizinone derivative is presented as an illustrative example for handling and describing the modulated structure of a typical pharmaceutical (i.e. molecular) compound. Having established a working knowledge of the concepts and terminology of the superspace approach a concise and detailed description of the complete process of peak indexing, data processing, structure solution and structure interpretation is presented for the incommensurately modulated crystal structure of the above-mentioned compound. The superspace symmetry applied is P21(α0γ)0; the (incommensurate) q vector components at 100 K are α = 0.1422 (2) and γ = 0.3839 (8). text/html A non-mathematical introduction to the superspace description of modulated structures text 65 3 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2009-06-01 249 feature articles 0108-7681 med@iucr.org 268 1600-5740 http://scripts.iucr.org/cgi-bin/paper?pf0072 Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Liebau, F. 2009-06-01 doi:10.1107/S0108768109012208 International Union of Crystallography en BOOK REVIEW text/html Structural Crystallography of Inorganic Oxysalts. By S. V. Krivovichev. Vol. 22, IUCr Monographs on Crystallography. Oxford University Press, 2009. Price (hardback) GBP 65.00. ISBN 978-0-19-921320-7. text 65 3 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2009-06-01 403 book reviews 0108-7681 med@iucr.org 403 1600-5740 http://scripts.iucr.org/cgi-bin/paper?kd5026 The weberite structure (A2B2X7) is an anion-deficient fluorite-related superstructure. Compared with fluorites, the reduction in the number of anions leads to a decrease in the coordination number of the B cations (VI coordination) with respect to the A cations (VIII coordination), thus allowing the accommodation of diverse cations. As a result, weberite compounds have a broad range of chemical and physical properties and great technological potential. This article summarizes the structural features of weberite and describes the structure in several different ways. This is the first time that the stacking vector and stacking angle are used to represent the weberite structure. This paper also discusses the crystallographic relationship between weberite, fluorite and pyrochlore (another fluorite-related structure). The cation sublattices of weberite and pyrochlore are correlated by an axial transformation. It has been shown that the different coordination environment of anions is due to the alternating layering of the AB3 and A3B close-packed cation layers. A stability field of weberite oxides is proposed in terms of the ratio of ionic radius of cations and relative bond ionicity. In addition, a selection of weberite compounds with interesting properties is discussed. Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Cai, L. Nino, J.C. 2009-06-01 doi:10.1107/S0108768109011355 International Union of Crystallography This article focuses on weberite ceramics. The structural features of weberite, its relationship to the fluorite and the pyrochlore structures, and some weberite ceramics with interesting properties are discussed. en WEBERITE STRUCTURE; CERAMICS; COORDINATION ENVIRONMENT; RELATIVE BOND IONICITY The weberite structure (A2B2X7) is an anion-deficient fluorite-related superstructure. Compared with fluorites, the reduction in the number of anions leads to a decrease in the coordination number of the B cations (VI coordination) with respect to the A cations (VIII coordination), thus allowing the accommodation of diverse cations. As a result, weberite compounds have a broad range of chemical and physical properties and great technological potential. This article summarizes the structural features of weberite and describes the structure in several different ways. This is the first time that the stacking vector and stacking angle are used to represent the weberite structure. This paper also discusses the crystallographic relationship between weberite, fluorite and pyrochlore (another fluorite-related structure). The cation sublattices of weberite and pyrochlore are correlated by an axial transformation. It has been shown that the different coordination environment of anions is due to the alternating layering of the AB3 and A3B close-packed cation layers. A stability field of weberite oxides is proposed in terms of the ratio of ionic radius of cations and relative bond ionicity. In addition, a selection of weberite compounds with interesting properties is discussed. text/html Complex ceramic structures. I. Weberites text 65 3 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2009-06-01 269 feature articles 0108-7681 med@iucr.org 290 1600-5740 http://scripts.iucr.org/cgi-bin/paper?kd5031 Systematic variations of the bond-valence sums calculated from the poorly determined bond-valence parameters [Sidey (2008), Acta Cryst. B64, 515–518] have been illustrated using a simple graphical scheme. Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Sidey, V. 2009-06-01 doi:10.1107/S0108768109008581 International Union of Crystallography Systematic variations of the bond-valence sums calculated from the poorly determined bond-valence parameters have been illustrated using a simple graphical scheme. en BOND-VALENCE MODEL; ECCENTRICITY PARAMETERS; POLYHEDRON DISTORTION Systematic variations of the bond-valence sums calculated from the poorly determined bond-valence parameters [Sidey (2008), Acta Cryst. B64, 515–518] have been illustrated using a simple graphical scheme. text/html On the correlations between the polyhedron eccentricity parameters and the bond-valence sums for the cations with one lone electron pair. Addendum text 65 3 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2009-06-01 401 addenda and errata 0108-7681 med@iucr.org 402 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bk5081 We report on the organization and outcome of the fourth blind test of crystal structure prediction, an international collaborative project organized to evaluate the present state in computational methods of predicting the crystal structures of small organic molecules. There were 14 research groups which took part, using a variety of methods to generate and rank the most likely crystal structures for four target systems: three single-component crystal structures and a 1:1 cocrystal. Participants were challenged to predict the crystal structures of the four systems, given only their molecular diagrams, while the recently determined but as-yet unpublished crystal structures were withheld by an independent referee. Three predictions were allowed for each system. The results demonstrate a dramatic improvement in rates of success over previous blind tests; in total, there were 13 successful predictions and, for each of the four targets, at least two groups correctly predicted the observed crystal structure. The successes include one participating group who correctly predicted all four crystal structures as their first ranked choice, albeit at a considerable computational expense. The results reflect important improvements in modelling methods and suggest that, at least for the small and fairly rigid types of molecules included in this blind test, such calculations can be constructively applied to help understand crystallization and polymorphism of organic molecules. Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Day, G.M. Cooper, T.G. Cruz-Cabeza, A.J. Hejczyk, K.E. Ammon, H.L. Boerrigter, S.X.M. Tan, J.S. Della Valle, R.G. Venuti, E. Jose, J. Gadre, S.R. Desiraju, G.R. Thakur, T.S. van Eijck, B.P. Facelli, J.C. Bazterra, V.E. Ferraro, M.B. Hofmann, D.W.M. Neumann, M.A. Leusen, F.J.J. Kendrick, J. Price, S.L. Misquitta, A.J. Karamertzanis, P.G. Welch, G.W.A. Scheraga, H.A. Arnautova, Y.A. Schmidt, M.U. van de Streek, J. Wolf, A.K. Schweizer, B. 2009-04-01 doi:10.1107/S0108768109004066 International Union of Crystallography The findings of the fourth blind test of crystal structure prediction, which have demonstrated important progress in computational methods, are presented and discussed. en PREDICTION; BLIND TEST; POLYMORPH We report on the organization and outcome of the fourth blind test of crystal structure prediction, an international collaborative project organized to evaluate the present state in computational methods of predicting the crystal structures of small organic molecules. There were 14 research groups which took part, using a variety of methods to generate and rank the most likely crystal structures for four target systems: three single-component crystal structures and a 1:1 cocrystal. Participants were challenged to predict the crystal structures of the four systems, given only their molecular diagrams, while the recently determined but as-yet unpublished crystal structures were withheld by an independent referee. Three predictions were allowed for each system. The results demonstrate a dramatic improvement in rates of success over previous blind tests; in total, there were 13 successful predictions and, for each of the four targets, at least two groups correctly predicted the observed crystal structure. The successes include one participating group who correctly predicted all four crystal structures as their first ranked choice, albeit at a considerable computational expense. The results reflect important improvements in modelling methods and suggest that, at least for the small and fairly rigid types of molecules included in this blind test, such calculations can be constructively applied to help understand crystallization and polymorphism of organic molecules. text/html Significant progress in predicting the crystal structures of small organic molecules – a report on the fourth blind test text 65 2 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2009-04-01 107 feature articles 0108-7681 med@iucr.org 125 1600-5740 http://scripts.iucr.org/cgi-bin/paper?wh5001 The bixbyite structure (Mn2O3) (Ia\bar 3) is often described as a distorted face-centered cubic (f.c.c.) array of Mn atoms, with O atoms occupying 3/4 of the tetrahedral holes. The empty M4 tetrahedra are centred at 16c. In anti-bixbyite structures (Mg3N2), cation vacancies are centred in empty N4 tetrahedra. If 16 hypothetical atoms were located at this site they would form the structure of γ-Si. This means that anti-bixbyite structures are ideally prepared to accommodate Si(Ge) atoms at these holes. Several compounds (Li3AlN2 and Li3ScN2) fully satisfy this expectation. They are really anti-bixbyites `stuffed' with Al(Sc). The presence of these atoms in 16c is illuminated in the light of the extended Zintl–Klemm concept (EZKC) [Vegas & García-Baonza (2007). Acta Cryst. B63, 339–345], from which a compound would be the result of `multiple resonance' pseudo-structures, emerging from electron transfers between any species pair (like or unlike atoms, cations or anions). The coordination-defect (CD) concept [Bevan & Martin (2008). J. Solid State Chem. 181, 2250–2259] is also consistent with the EZKC description of the pseudo-structures. A more profound insight into crystal structures is gained if one is not restricted to the contemplation of classical anions and cations in their conventional oxidation states. http://creativecommons.org/licenses/by/2.0/uk urn:issn:0108-7681 Vegas, A. Martin, R.L. Bevan, D.J.M. 2009-02-01 doi:10.1107/S010876810803423X International Union of Crystallography Compounds with a `stuffed anti-bixbyite' structure, such as Li3AlN2, were analysed in terms of both the extended Zintl–Klemm concept and the coordination-defect concept. For the first time, inorganic crystal structures are seen as a set of `multiple resonance structures' (Klemm pseudo-structures) which co-exist as the result of unexpected electron transfers between any species pair comprising either like or unlike atoms, cations or anions. If this is the driving force controlling crystal structures, the conventional oxidation states assigned to cations and anions lose some of their usefulness. en ZINTL-KLEMM CONCEPT; COORDINATION-DEFECT CONCEPT; MULTIPLE RESONANCE STRUCTURE; ELECTRON TRANSFER The bixbyite structure (Mn2O3) (Ia\bar 3) is often described as a distorted face-centered cubic (f.c.c.) array of Mn atoms, with O atoms occupying 3/4 of the tetrahedral holes. The empty M4 tetrahedra are centred at 16c. In anti-bixbyite structures (Mg3N2), cation vacancies are centred in empty N4 tetrahedra. If 16 hypothetical atoms were located at this site they would form the structure of γ-Si. This means that anti-bixbyite structures are ideally prepared to accommodate Si(Ge) atoms at these holes. Several compounds (Li3AlN2 and Li3ScN2) fully satisfy this expectation. They are really anti-bixbyites `stuffed' with Al(Sc). The presence of these atoms in 16c is illuminated in the light of the extended Zintl–Klemm concept (EZKC) [Vegas & García-Baonza (2007). Acta Cryst. B63, 339–345], from which a compound would be the result of `multiple resonance' pseudo-structures, emerging from electron transfers between any species pair (like or unlike atoms, cations or anions). The coordination-defect (CD) concept [Bevan & Martin (2008). J. Solid State Chem. 181, 2250–2259] is also consistent with the EZKC description of the pseudo-structures. A more profound insight into crystal structures is gained if one is not restricted to the contemplation of classical anions and cations in their conventional oxidation states. text/html Compounds with a `stuffed' anti-bixbyite-type structure, analysed in terms of the Zintl–Klemm and coordination-defect concepts text 65 1 http://creativecommons.org/licenses/by/2.0/uk Acta Crystallographica Section B: Structural Science 2009-02-01 11 research papers 0108-7681 med@iucr.org 21 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bp5012 Ammonium oxopentafluoroniobate, (NH4)2NbOF5, was synthesized in a single-crystal form and the structures of its different phases were determined by X-ray diffraction at three temperatures: phase (I) at 297 K, phase (II) at 233 K and phase (III) at 198 K. The distorted [NbOF5]2− octahedra are of similar geometry in all three structures, with the central atom shifted towards the O atom. The structure of (I) is disordered, with three spatial orientations of the [NbOF5]2− octahedron related by a jump rotation around the pseudo-threefold local axis such that the disorder observed is of a dynamic nature. As the temperature decreases, the compound undergoes two phase transitions. The first is accompanied by full anionic ordering and partial ordering of the ammonium groups (phase II). The structure of (III) is completely ordered. The F and O atoms in the structures investigated were identified via the Nb—X (X = O and F) distances. The crystals of all three phases are twinned. http://creativecommons.org/licenses/by/2.0/uk urn:issn:0108-7681 Udovenko, A.A. Laptash, N.M. 2008-10-01 doi:10.1107/S0108768108021289 International Union of Crystallography Structural phase transitions in a crystal of (NH4)2NbOF5 are the consequence of dynamic changes in its structural units as the temperature decreases. Using X-ray diffraction, it is possible to identify O and F atoms in the disordered structure of (NH4)2NbOF5 as a result of its dynamic nature. en AMMONIUM OXOPENTAFLUORONIOBATE; DISTORTED OCTAHEDRA; DYNAMIC ORIENTATIONAL DISORDER; PHASE TRANSITIONS; TWINNING; VIBRATIONAL SPECTRA Ammonium oxopentafluoroniobate, (NH4)2NbOF5, was synthesized in a single-crystal form and the structures of its different phases were determined by X-ray diffraction at three temperatures: phase (I) at 297 K, phase (II) at 233 K and phase (III) at 198 K. The distorted [NbOF5]2− octahedra are of similar geometry in all three structures, with the central atom shifted towards the O atom. The structure of (I) is disordered, with three spatial orientations of the [NbOF5]2− octahedron related by a jump rotation around the pseudo-threefold local axis such that the disorder observed is of a dynamic nature. As the temperature decreases, the compound undergoes two phase transitions. The first is accompanied by full anionic ordering and partial ordering of the ammonium groups (phase II). The structure of (III) is completely ordered. The F and O atoms in the structures investigated were identified via the Nb—X (X = O and F) distances. The crystals of all three phases are twinned. text/html Orientational disorder and phase transitions in crystals of (NH4)2NbOF5 text 64 5 http://creativecommons.org/licenses/by/2.0/uk Acta Crystallographica Section B: Structural Science 2008-10-01 527 research papers 0108-7681 med@iucr.org 533 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bs9048 A corrigendum to the paper by Meents et al. (2008), Acta Cryst. B64, 42–49 to correct the nomenclature for CL-20. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7681 Meents, A. Dittrich, B. Johnas, S.K.J. Thome, V. Weckert, E.F. 2008-08-01 doi:10.1107/S0108768108017497 International Union of Crystallography A corrigendum to the paper by Meents et al. (2008), Acta Cryst. B64, 42–49. en ENERGETIC MATERIALS; TOPOLOGICAL ANALYSIS; CHARGE DENSITY A corrigendum to the paper by Meents et al. (2008), Acta Cryst. B64, 42–49 to correct the nomenclature for CL-20. text/html Charge-density studies of energetic materials: CL-20 and FOX-7. Corrigendum text 64 4 Copyright (c) 2008 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2008-08-01 519 addenda and errata 0108-7681 med@iucr.org 519 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bk5056 Monte Carlo computer simulation has been used to interpret and model observed single-crystal diffuse X-ray scattering data for pentachloronitrobenzene, C6Cl5NO2. Each site in the crystal contains a molecule in one of six different basic orientations with equal probability. However, no short-range order amongst these different orientations has been detected. The strong, detailed and very distinctive diffraction patterns can be accounted for almost entirely on the assumption of random occupancy of each molecular site, but with very large local relaxation displacements that tend to increase the neighbouring distances for contacts involving NO2⋯NO2 and NO2⋯Cl with a corresponding reduction for those involving Cl⋯Cl. The results show that the mean NO2⋯NO2 distance is increased by ∼ 0.6 Å, compared with that given by the average structure determination. Copyright (c) 2007 International Union of Crystallography urn:issn:0108-7681 Thomas, L.H. Welberry, T.R. Goossens, D.J. Heerdegen, A.P. Gutmann, M.J. Teat, S.J. Lee, P.L. Wilson, C.C. Cole, J.M. 2007-08-01 doi:10.1107/S0108768107024305 International Union of Crystallography Monte Carlo computer simulation has been used to interpret and model observed single-crystal diffuse X-ray scattering data for pentachloronitrobenzene, C6Cl5NO2. The strong, detailed and very distinctive diffraction patterns can be accounted for almost entirely on the assumption of the random occupancy of each molecular site, but with very large local relaxation displacements that tend to increase the neighbouring distances for contacts involving NO2⋯NO2 and NO2⋯Cl with a corresponding reduction for those involving Cl⋯Cl. en DISORDER; DIFFUSE SCATTERING STUDY; MONTE CARLO COMPUTER SIMULATION; RELAXATION DISPLACEMENTS Monte Carlo computer simulation has been used to interpret and model observed single-crystal diffuse X-ray scattering data for pentachloronitrobenzene, C6Cl5NO2. Each site in the crystal contains a molecule in one of six different basic orientations with equal probability. However, no short-range order amongst these different orientations has been detected. The strong, detailed and very distinctive diffraction patterns can be accounted for almost entirely on the assumption of random occupancy of each molecular site, but with very large local relaxation displacements that tend to increase the neighbouring distances for contacts involving NO2⋯NO2 and NO2⋯Cl with a corresponding reduction for those involving Cl⋯Cl. The results show that the mean NO2⋯NO2 distance is increased by ∼ 0.6 Å, compared with that given by the average structure determination. text/html Disorder in pentachloronitrobenzene, C6Cl5NO2: a diffuse scattering study text 63 4 Copyright (c) 2007 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2007-08-01 663 research papers 0108-7681 med@iucr.org 673 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bk5053 The generalization of the Zintl–Klemm concept provides a universal formulation of a crystal structure in terms of universal building skeletons formed by Klemm's pseudoatoms: atoms that behave structurally according to their formal total electron charge. An important difference in this novel view is that charge is considered to be transferred, in the strict Zintl's sense, from the donor cations to the building skeleton as a whole, not specifically to a given atom or ion. Although application is restricted to (IV)–(IV) compounds (group 14 structures), the principle seems to be universal and can be applied to understand, to relate and to predict the structure of complex compounds on the basis of more simple structures, e.g. a given AB skeleton provides the building block for A2B, AB2, ABXm etc. compounds of a very different nature. The application of such a principle only requires information on the constituent atoms and on the existing phases of the p-block elements (observed under ambient and high-pressure and/or high-temperature conditions). The ideas introduced here demonstrate, for the first time, that a generalization of the Zintl–Klemm concept is possible and that such a generalization helps to establish a univocal link between chemical composition (in terms of pseudoatoms) and the crystalline structures observed experimentally. Copyright (c) 2007 International Union of Crystallography urn:issn:0108-7681 Vegas, A. García-Baonza, V. 2007-06-01 doi:10.1107/S0108768107019167 International Union of Crystallography A generalization of the Zintl–Klemm concept (ZKC) explains the complex structures of alloys as well as the cation arrays of oxides. This generalization helps to establish a univocal link between chemical composition (in terms of Klemm's pseudoatoms) and the structures observed experimentally. en PHASE TRANSITIONS; ZINTL-KLEMM CONCEPT; CATION ARRAYS The generalization of the Zintl–Klemm concept provides a universal formulation of a crystal structure in terms of universal building skeletons formed by Klemm's pseudoatoms: atoms that behave structurally according to their formal total electron charge. An important difference in this novel view is that charge is considered to be transferred, in the strict Zintl's sense, from the donor cations to the building skeleton as a whole, not specifically to a given atom or ion. Although application is restricted to (IV)–(IV) compounds (group 14 structures), the principle seems to be universal and can be applied to understand, to relate and to predict the structure of complex compounds on the basis of more simple structures, e.g. a given AB skeleton provides the building block for A2B, AB2, ABXm etc. compounds of a very different nature. The application of such a principle only requires information on the constituent atoms and on the existing phases of the p-block elements (observed under ambient and high-pressure and/or high-temperature conditions). The ideas introduced here demonstrate, for the first time, that a generalization of the Zintl–Klemm concept is possible and that such a generalization helps to establish a univocal link between chemical composition (in terms of pseudoatoms) and the crystalline structures observed experimentally. text/html Pseudoatoms and preferred skeletons in crystals text 63 3 Copyright (c) 2007 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2007-06-01 339 feature articles 0108-7681 med@iucr.org 345 1600-5740 http://scripts.iucr.org/cgi-bin/paper?og5020 The crystal structure of the compositionally homogeneous ceria–zirconia solid solution CeZrO4 is refined by Rietveld analysis of neutron diffraction data measured in situ over the temperature range 296–1831 K. The CeZrO4 exhibits a tetragonal structure with the space group P42/nmc at temperatures from 296 to 1542 K (Z = 1), and a cubic fluorite-type form with the space group Fm\overline 3 m at 1831 K (Z = 2). The isotropic atomic displacement parameters of Ce and Zr atoms B(Ce,Zr) and O atoms B(O) are found to increase with temperature, with B(O) being larger than B(Ce,Zr), suggesting the higher diffusivity of oxygen ions. The ratio of the c axial length to the a length of the pseudo-fluorite lattice (c/aF axial ratio) for the tetragonal CeZrO4 phase increased from 296 to 1034 K and decreased from 1291 to 1542 K, reaching unity between 1542 and 1831 K. The displacement of O atoms along the c axis in the tetragonal CeZrO4 phase increased from 296 to 1034 K and decreased from 1291 to 1542 K, reaching 0.0 Å between 1542 and 1831 K. These results indicate that the cubic-to-tetragonal phase transition between 1542 and 1831 K is accompanied by oxygen displacement along the c axis and the increase of the c/aF axial ratio from unity. Copyright (c) 2007 International Union of Crystallography urn:issn:0108-7681 Wakita, T. Yashima, M. 2007-06-01 doi:10.1107/S0108768107007720 International Union of Crystallography The crystal structure of the ceria–zirconia solid solution CeZrO4 is refined by Rietveld analysis of neutron diffraction data measured in situ over the temperature range 296–1831 K. The cubic-to-tetragonal phase transition between 1542 and 1831 K is accompanied by the displacement of oxygen atoms and elongation of the c axis. en PHASE TRANSITION; NEUTRON DIFFRACTION; HIGH-TEMPERATURE MATERIALS The crystal structure of the compositionally homogeneous ceria–zirconia solid solution CeZrO4 is refined by Rietveld analysis of neutron diffraction data measured in situ over the temperature range 296–1831 K. The CeZrO4 exhibits a tetragonal structure with the space group P42/nmc at temperatures from 296 to 1542 K (Z = 1), and a cubic fluorite-type form with the space group Fm\overline 3 m at 1831 K (Z = 2). The isotropic atomic displacement parameters of Ce and Zr atoms B(Ce,Zr) and O atoms B(O) are found to increase with temperature, with B(O) being larger than B(Ce,Zr), suggesting the higher diffusivity of oxygen ions. The ratio of the c axial length to the a length of the pseudo-fluorite lattice (c/aF axial ratio) for the tetragonal CeZrO4 phase increased from 296 to 1034 K and decreased from 1291 to 1542 K, reaching unity between 1542 and 1831 K. The displacement of O atoms along the c axis in the tetragonal CeZrO4 phase increased from 296 to 1034 K and decreased from 1291 to 1542 K, reaching 0.0 Å between 1542 and 1831 K. These results indicate that the cubic-to-tetragonal phase transition between 1542 and 1831 K is accompanied by oxygen displacement along the c axis and the increase of the c/aF axial ratio from unity. text/html In situ observation of the tetragonal–cubic phase transition in the CeZrO4 solid solution – a high-temperature neutron diffraction study text 63 3 Copyright (c) 2007 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2007-06-01 384 research papers 0108-7681 med@iucr.org 389 1600-5740 http://scripts.iucr.org/cgi-bin/paper?ws5049 1-(2-Chloronicotinoyl)-2-(2-nitrophenyl)hydrazine, C12H9Cl­N4O3, crystallizes in three polymorphic forms, two monoclinic forms in space groups Cc (Ia) and P21 (Ib), and an orthorhombic form in space group Pbcn (Ic). In the Cc polymorph (Ia) the molecules are linked into sheets by combinations of one N—H⋯O and two C—H⋯O hydrogen bonds, while in the P21 polymorph (Ib) the molecules are linked into sheets by combinations of three hydrogen bonds, one each of N—H⋯O, C—H⋯N and C—H⋯O types. In the orthorhombic polymorph (Ic) the molecules are linked into a complex three-dimensional framework structure by a combination of one N—H⋯O, one N—H⋯N and three C—H⋯O hydrogen bonds, and an aromatic π⋯π stacking interaction. In the isomeric compound 1-(2-chloronicotinoyl)-2-(3-nitrophenyl)hydrazine (II) the molecules are again linked into a three-dimensional framework, this time by a combination of three hydrogen bonds, one each of N—H⋯O, N—H⋯N and C—H⋯O types, weakly augmented by a π⋯π stacking interaction. The molecules of 1-(2-chloronicotinoyl)-2-(4-nitrophenyl)hydrazine (III) are linked into sheets by a combination of three hydrogen bonds, one each of N—H⋯O, N—H⋯N and C—H⋯O types. Copyright (c) 2007 International Union of Crystallography urn:issn:0108-7681 Wardell, S.M.S.V. Souza, M.V.N. de Wardell, J.L. Low, J.N. Glidewell, C. 2007-02-01 doi:10.1107/S0108768106041358 International Union of Crystallography In isomeric 1-(2-chloronicotinoyl)-2-(nitrophenyl)hydrazines, the molecules may be linked into supramolecular structures in two or three dimensions by various combinations of N—H⋯O, N—H⋯N, C—H⋯N and C—H⋯O hydrogen bonds, sometimes augmented by π⋯π stacking interactions. en GEOMETRICAL ISOMERS; HYDROGEN BONDING; PHENYLHYDRAZINE; POLYMORPHISM; SUPRAMOLECULAR STRUCTURES 1-(2-Chloronicotinoyl)-2-(2-nitrophenyl)hydrazine, C12H9Cl­N4O3, crystallizes in three polymorphic forms, two monoclinic forms in space groups Cc (Ia) and P21 (Ib), and an orthorhombic form in space group Pbcn (Ic). In the Cc polymorph (Ia) the molecules are linked into sheets by combinations of one N—H⋯O and two C—H⋯O hydrogen bonds, while in the P21 polymorph (Ib) the molecules are linked into sheets by combinations of three hydrogen bonds, one each of N—H⋯O, C—H⋯N and C—H⋯O types. In the orthorhombic polymorph (Ic) the molecules are linked into a complex three-dimensional framework structure by a combination of one N—H⋯O, one N—H⋯N and three C—H⋯O hydrogen bonds, and an aromatic π⋯π stacking interaction. In the isomeric compound 1-(2-chloronicotinoyl)-2-(3-nitrophenyl)hydrazine (II) the molecules are again linked into a three-dimensional framework, this time by a combination of three hydrogen bonds, one each of N—H⋯O, N—H⋯N and C—H⋯O types, weakly augmented by a π⋯π stacking interaction. The molecules of 1-(2-chloronicotinoyl)-2-(4-nitrophenyl)hydrazine (III) are linked into sheets by a combination of three hydrogen bonds, one each of N—H⋯O, N—H⋯N and C—H⋯O types. text/html Three isomeric 1-(2-chloronicotinoyl)-2-(nitro­phenyl)hydrazines, including three polymorphs of 1-(2-chloronicotinoyl)-2-(2-nitrophenyl)hydrazine: hydrogen-bonded supramolecular structures in two and three dimensions text 63 1 Copyright (c) 2007 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2007-02-01 101 research papers 0108-7681 med@iucr.org 110 1600-5740 http://scripts.iucr.org/cgi-bin/paper?gp5013 The structures of five polyiodide salts, [Co([9]aneS3)2]I11 (1), [Ni([9]aneS3)2]I6 (2), [Ni([9]aneS3)2]I10 (3), [Pd([12]aneS4)]I6 (4) and [Pd([14]aneS4)]I10·MeCN (5), containing the template cations [Co([9]aneS3)2]3+, [Ni([9]aneS3)2]2+, [Pd([12]aneS4)]2+ and [Pd([14]aneS4)]2+ ([9]aneS3 = 1,4,7-trithiacyclononane, [12]aneS4 = 1,4,7,10-tetrathiacyclododecane, [14]aneS4 = 1,4,8,11-tetrathiacyclotetradecane) exhibit a range of polyiodide and polyanionic framework structures. In (1) the charge on the CoIII cation is balanced by three I_3^- anions, which along with a neutral di-iodine molecule form I_{11}^{3-} rings in an extended structure comprising undulating chains of alternating I_{11}^{3-} rings and complex cations. In (2) the complex cation is linked to two tri-iodide anions by S⋯I interactions into well separated sheets of cations and anions, while in (3), I_5^- anions are linked by I⋯I interactions into helices which are cross-linked by S⋯I contacts to form sheets. Rather longer I⋯I contacts in (4) assemble I_3^- ions into 2 × 2 rods, which are linked into a three-dimensional network by S⋯I contacts. In (5) the N atom of the acetonitrile solvent molecule forms an array of four weak C—H⋯N hydrogen bonds to the macrocycle. The extended structure comprises corrugated zigzag chains of polyiodide rings formed by linked I_5^- units; the complex cations are attached to the polyiodide network by S⋯I contacts, which link the chains to form layers. Copyright (c) 2007 International Union of Crystallography urn:issn:0108-7681 Blake, A.J. Li, W.-S. Lippolis, V. Parsons, S. Schröder, M. 2007-02-01 doi:10.1107/S0108768106041668 International Union of Crystallography Complex cations of transition metals with thioether macrocycles act as templates for the assembly of a wide range of polyiodide anions and their polyanionic networks. en TEMPLATE EFFECT; POLYIODIDES; FRAMEWORK; SELF-ASSEMBLY; HELICITY The structures of five polyiodide salts, [Co([9]aneS3)2]I11 (1), [Ni([9]aneS3)2]I6 (2), [Ni([9]aneS3)2]I10 (3), [Pd([12]aneS4)]I6 (4) and [Pd([14]aneS4)]I10·MeCN (5), containing the template cations [Co([9]aneS3)2]3+, [Ni([9]aneS3)2]2+, [Pd([12]aneS4)]2+ and [Pd([14]aneS4)]2+ ([9]aneS3 = 1,4,7-trithiacyclononane, [12]aneS4 = 1,4,7,10-tetrathiacyclododecane, [14]aneS4 = 1,4,8,11-tetrathiacyclotetradecane) exhibit a range of polyiodide and polyanionic framework structures. In (1) the charge on the CoIII cation is balanced by three I_3^- anions, which along with a neutral di-iodine molecule form I_{11}^{3-} rings in an extended structure comprising undulating chains of alternating I_{11}^{3-} rings and complex cations. In (2) the complex cation is linked to two tri-iodide anions by S⋯I interactions into well separated sheets of cations and anions, while in (3), I_5^- anions are linked by I⋯I interactions into helices which are cross-linked by S⋯I contacts to form sheets. Rather longer I⋯I contacts in (4) assemble I_3^- ions into 2 × 2 rods, which are linked into a three-dimensional network by S⋯I contacts. In (5) the N atom of the acetonitrile solvent molecule forms an array of four weak C—H⋯N hydrogen bonds to the macrocycle. The extended structure comprises corrugated zigzag chains of polyiodide rings formed by linked I_5^- units; the complex cations are attached to the polyiodide network by S⋯I contacts, which link the chains to form layers. text/html Extended structures of polyiodide salts of transition metal macrocyclic complexes text 63 1 Copyright (c) 2007 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2007-02-01 81 research papers 0108-7681 med@iucr.org 92 1600-5740 http://scripts.iucr.org/cgi-bin/paper?ws5045 High-resolution neutron powder diffraction has been used in order to characterize the order–disorder transition in monoclinic cyclo-octasulphur. Rapid data collection and the novel use of geometrically constrained refinements has enabled a direct and precise determination of the order parameter, based on molecular site occupancies, to be made. The transition is critical and continuous; with a transition temperature, Tc = 198.4 (3) K, and a critical exponent, β = 0.28 (3), which is indicative of three-dimensional ordering. Difficulties encountered as a consequence of the low thermal conductivity of the sample are discussed. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 David, W.I.F. Ibberson, R.M. Cox, S.F.J. Wood, P.T. 2006-12-01 doi:10.1107/S0108768106039309 International Union of Crystallography The order–disorder phase transition in monoclinic β-sulfur has been characterized using high-resolution neutron powder diffraction. The transition is critical and continuous, with a transition temperature, Tc = 198.4 (3) K, and a critical exponent, β = 0.28 (3), which is indicative of three-dimensional ordering. en NEUTRON POWDER DIFFRACTION; LOW-TEMPERATURE CRYSTALLOGRAPHY; CRITICAL PHENOMENA; PHASE TRANSITION High-resolution neutron powder diffraction has been used in order to characterize the order–disorder transition in monoclinic cyclo-octasulphur. Rapid data collection and the novel use of geometrically constrained refinements has enabled a direct and precise determination of the order parameter, based on molecular site occupancies, to be made. The transition is critical and continuous; with a transition temperature, Tc = 198.4 (3) K, and a critical exponent, β = 0.28 (3), which is indicative of three-dimensional ordering. Difficulties encountered as a consequence of the low thermal conductivity of the sample are discussed. text/html Order–disorder transition in monoclinic sulfur: a precise structural study by high-resolution neutron powder diffraction text 62 6 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-12-01 953 research papers 0108-7681 med@iucr.org 959 1600-5740 http://scripts.iucr.org/cgi-bin/paper?ws5047 The structure of strontium barium niobate crystals SrxBa1 − xNb2O6 is comprehensively studied in the whole range of the tetragonal tungsten bronze phase (x = 0.32–0.82) using both powder and single-crystal X-ray diffraction measurements. Unit-cell parameters, density, site-occupancy factors and interionic distances show an explicit composition dependence which can be consistently explained using simple model calculations. The temperature dependence of the unit-cell parameters exhibits a remarkable anisotropy in a broad temperature region below the phase transition temperature. This proves that the electrostrictive contribution to the thermal expansion plays an important role in strontium barium niobate. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Podlozhenov, S. Graetsch, H.A. Schneider, J. Ulex, M. Wöhlecke, M. Betzler, K. 2006-12-01 doi:10.1107/S0108768106038869 International Union of Crystallography The structure of strontium barium niobate crystals is studied in the whole range of the tetragonal tungsten bronze phase using X-ray diffraction measurements. Unit-cell parameters, density, site-occupancy factors and interionic distances show pronounced composition dependencies which are explained by model calculations. en TUNGSTEN BRONZE; SINGLE CRYSTAL GROWTH; NIOBATES; FERROELECTRIC MATERIALS The structure of strontium barium niobate crystals SrxBa1 − xNb2O6 is comprehensively studied in the whole range of the tetragonal tungsten bronze phase (x = 0.32–0.82) using both powder and single-crystal X-ray diffraction measurements. Unit-cell parameters, density, site-occupancy factors and interionic distances show an explicit composition dependence which can be consistently explained using simple model calculations. The temperature dependence of the unit-cell parameters exhibits a remarkable anisotropy in a broad temperature region below the phase transition temperature. This proves that the electrostrictive contribution to the thermal expansion plays an important role in strontium barium niobate. text/html Structure of strontium barium niobate SrxBa1 − xNb2O6 (SBN) in the composition range 0.32 ≤ x ≤ 0.82 text 62 6 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-12-01 960 research papers 0108-7681 med@iucr.org 965 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bm5038 The solvothermal synthesis of four two-dimensional metal-organic frameworks containing linear dicarboxylic acids as ligands for ZnII centres is described. Zn(BDC)(DMF) [(1) where BDC = benzene-1,4-dicarboxylic acid; DMF = N,N-dimethylformamide] adopts a common paddlewheel motif leading to a 44 grid network, whereas Zn3(BDC)3(EtOH)2 (2), Zn3(BDC)3(H2O)2·4DMF (3) and Zn3(BPDC)3(DMF)2·4DMF (4) each form networks with the relatively uncommon 36 topology based upon Zn3(O2CR)6 secondary building units. All contain coordinated solvent molecules, namely DMF [(1) and (4)], ethanol (2) or H2O (3). Comparison of structures (2) and (3) illustrates a clay-like flexibility in interplanar spacing which sheds light on the ability of the Zn3(BDC)3 framework to undergo desolvation and uptake of small solvent and gas molecules. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Hawxwell, S.M. Adams, H. Brammer, L. 2006-10-01 doi:10.1107/S0108768106033283 International Union of Crystallography Metal-organic framework structures adopting either square grid or triangular grid architectures are reported. A family of the latter type incorporating different solvent molecules sheds light on the flexibility of these layered structures in previously reported solvent loss/uptake. en SOLVOTHERMAL SYNTHESIS; METAL-ORGANIC FRAMEWORKS The solvothermal synthesis of four two-dimensional metal-organic frameworks containing linear dicarboxylic acids as ligands for ZnII centres is described. Zn(BDC)(DMF) [(1) where BDC = benzene-1,4-dicarboxylic acid; DMF = N,N-dimethylformamide] adopts a common paddlewheel motif leading to a 44 grid network, whereas Zn3(BDC)3(EtOH)2 (2), Zn3(BDC)3(H2O)2·4DMF (3) and Zn3(BPDC)3(DMF)2·4DMF (4) each form networks with the relatively uncommon 36 topology based upon Zn3(O2CR)6 secondary building units. All contain coordinated solvent molecules, namely DMF [(1) and (4)], ethanol (2) or H2O (3). Comparison of structures (2) and (3) illustrates a clay-like flexibility in interplanar spacing which sheds light on the ability of the Zn3(BDC)3 framework to undergo desolvation and uptake of small solvent and gas molecules. text/html Two-dimensional metal-organic frameworks containing linear dicarboxylates text 62 5 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-10-01 808 research papers 0108-7681 med@iucr.org 814 1600-5740 http://scripts.iucr.org/cgi-bin/paper?so5004 The effect of pressure on the crystal structure of salicylaldoxime has been investigated. The ambient-pressure phase (salicylaldoxime-I) consists of pairs of molecules interacting through oximic OH⋯O hydrogen bonds; taken with phenolic OH⋯N intramolecular hydrogen bonds, these dimers form a pseudo-macrocycle bounded by an R_4^4 \left({10} \right) motif. The dimers interact principally via π⋯π stacking contacts. Salicylaldoxime derivatives are used industrially as selective solvent extractants for copper; the selectivity reflects the compatibility of the metal ion with the pseudo-macrocycle cavity size. On increasing the pressure to 5.28 GPa the size of the cavity was found to decrease by an amount comparable to the difference in hole sizes in the structures of the Cu2+ salicylaldoximato complex and its Ni2+ equivalent. On increasing the pressure to 5.93 GPa a new polymorph, salicylaldoxime-II, was obtained in a single-crystal to single-crystal phase transition. PIXEL calculations show that the phase transition is driven in part by relief of intermolecular repulsions in the dimer-forming OH⋯O-bonded ring motif, and the ten-centre hydrogen-bonding ring motif of the phase I structure is replaced in phase II by a six-centre ring formed by oximic OH⋯N hydrogen bonds. The transition also relieves repulsions in the π⋯π stacking contacts. The intramolecular OH⋯N hydrogen bond of phase I is replaced in phase II by a intermolecular phenolic OH⋯O hydrogen bond, but the total interaction energy of the pairs of molecules connected by this new contact is very slightly repulsive because the electrostatic hydrogen-bond energy is cancelled by the repulsion term. The intra- to intermolecular hydrogen-bond conversion simply promotes efficient packing rather than contributing to the overall lattice energy. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Wood, P.A. Forgan, R.S. Henderson, D. Parsons, S. Pidcock, E. Tasker, P.A. Warren, J.E. 2006-12-01 doi:10.1107/S0108768106031752 International Union of Crystallography The crystal structure of salicylaldoxime has been determined at room temperature at pressures from 0.75 to 5.28 GPa. Salicylaldoxime forms a pseudo-macrocycle which contains a cavity which decreases in size with pressure. Above 5.28 GPa the structure transforms to a new polymorph, the structure of which has been determined at 5.93 GPa. The changes in intermolecular interactions during the phase transition are interpreted with the aid of PIXEL calculations. en SALICYLALDOXIME; PRESSURE DEPENDENCE; PHASE TRANSITIONS; HYDROGEN BONDING The effect of pressure on the crystal structure of salicylaldoxime has been investigated. The ambient-pressure phase (salicylaldoxime-I) consists of pairs of molecules interacting through oximic OH⋯O hydrogen bonds; taken with phenolic OH⋯N intramolecular hydrogen bonds, these dimers form a pseudo-macrocycle bounded by an R_4^4 \left({10} \right) motif. The dimers interact principally via π⋯π stacking contacts. Salicylaldoxime derivatives are used industrially as selective solvent extractants for copper; the selectivity reflects the compatibility of the metal ion with the pseudo-macrocycle cavity size. On increasing the pressure to 5.28 GPa the size of the cavity was found to decrease by an amount comparable to the difference in hole sizes in the structures of the Cu2+ salicylaldoximato complex and its Ni2+ equivalent. On increasing the pressure to 5.93 GPa a new polymorph, salicylaldoxime-II, was obtained in a single-crystal to single-crystal phase transition. PIXEL calculations show that the phase transition is driven in part by relief of intermolecular repulsions in the dimer-forming OH⋯O-bonded ring motif, and the ten-centre hydrogen-bonding ring motif of the phase I structure is replaced in phase II by a six-centre ring formed by oximic OH⋯N hydrogen bonds. The transition also relieves repulsions in the π⋯π stacking contacts. The intramolecular OH⋯N hydrogen bond of phase I is replaced in phase II by a intermolecular phenolic OH⋯O hydrogen bond, but the total interaction energy of the pairs of molecules connected by this new contact is very slightly repulsive because the electrostatic hydrogen-bond energy is cancelled by the repulsion term. The intra- to intermolecular hydrogen-bond conversion simply promotes efficient packing rather than contributing to the overall lattice energy. text/html Effect of pressure on the crystal structure of salicylaldoxime-I, and the structure of salicylaldoxime-II at 5.93 GPa text 62 6 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-12-01 1099 research papers 0108-7681 med@iucr.org 1111 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bm5035 The isomeric N-(iodophenyl)nitrobenzamides, C13H9IN2O3, all form different three-dimensional framework structures. Molecules of N-(2-iodophenyl)-3-nitrobenzamide (II) are linked by a combination of N—H⋯O and C—H⋯O hydrogen bonds and a two-centre iodo⋯carbonyl interaction. The supramolecular structure of N-(2-iodophenyl)-4-nitrobenzamide (III) is built from one N—H⋯O and two C—H⋯O hydrogen bonds, but short I⋯O contacts are absent from the structure. In N-(3-iodophenyl)-2-nitrobenzamide (IV), which crystallizes with Z′ = 2 in space group P21, the structure contains two N—H⋯O hydrogen bonds, four C—H⋯O hydrogen bonds, two two-centre iodo⋯nitro interactions and an aromatic π⋯π stacking interaction. The structure of N-(3-iodophenyl)-3-nitrobenzamide (V) contains one N—H⋯O hydrogen bond and three C—H⋯O hydrogen bonds, together with a two-centre iodo⋯nitro interaction and an aromatic π⋯π stacking interaction, while in N-(3-iodophenyl)-4-nitrobenzamide (VI), the combination of one N—H⋯O hydrogen bond and two C—H⋯O hydrogen bonds is augmented not only by a two-centre iodo⋯nitro interaction and an aromatic π⋯π stacking interaction, but also by a dipolar carbonyl⋯carbonyl interaction. In the supramolecular structure of N-(4-iodophenyl)-4-nitrobenzamide (IX), which crystallizes with Z′ = 2 in space group P\overline 1, there are two N—H⋯O hydrogen bonds, four C—H⋯O hydrogen bonds and two three-centre iodo⋯nitro interactions. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Wardell, J.L. Low, J.N. Skakle, J.M.S. Glidewell, C. 2006-10-01 doi:10.1107/S0108768106029053 International Union of Crystallography Seven isomeric N-(iodophenyl)nitrobenzamides all display different direction-specific intermolecular interactions and all form different three-dimensional framework structures. en N-(IODOPHENYL)NITROBENZAMIDES The isomeric N-(iodophenyl)nitrobenzamides, C13H9IN2O3, all form different three-dimensional framework structures. Molecules of N-(2-iodophenyl)-3-nitrobenzamide (II) are linked by a combination of N—H⋯O and C—H⋯O hydrogen bonds and a two-centre iodo⋯carbonyl interaction. The supramolecular structure of N-(2-iodophenyl)-4-nitrobenzamide (III) is built from one N—H⋯O and two C—H⋯O hydrogen bonds, but short I⋯O contacts are absent from the structure. In N-(3-iodophenyl)-2-nitrobenzamide (IV), which crystallizes with Z′ = 2 in space group P21, the structure contains two N—H⋯O hydrogen bonds, four C—H⋯O hydrogen bonds, two two-centre iodo⋯nitro interactions and an aromatic π⋯π stacking interaction. The structure of N-(3-iodophenyl)-3-nitrobenzamide (V) contains one N—H⋯O hydrogen bond and three C—H⋯O hydrogen bonds, together with a two-centre iodo⋯nitro interaction and an aromatic π⋯π stacking interaction, while in N-(3-iodophenyl)-4-nitrobenzamide (VI), the combination of one N—H⋯O hydrogen bond and two C—H⋯O hydrogen bonds is augmented not only by a two-centre iodo⋯nitro interaction and an aromatic π⋯π stacking interaction, but also by a dipolar carbonyl⋯carbonyl interaction. In the supramolecular structure of N-(4-iodophenyl)-4-nitrobenzamide (IX), which crystallizes with Z′ = 2 in space group P\overline 1, there are two N—H⋯O hydrogen bonds, four C—H⋯O hydrogen bonds and two three-centre iodo⋯nitro interactions. text/html Isomeric N-(iodophenyl)nitrobenzamides form different three-dimensional framework structures text 62 5 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-10-01 931 research papers 0108-7681 med@iucr.org 943 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bs5035 The structural response of three members of the family of polycyclic aromatic hydrocarbons (PAHs) to high-pressure recrystallization from dichloromethane solutions is presented. Recrystallization of naphthalene in the 0.2–0.6 GPa pressure range does not result in the formation of a new polymorph. Furthermore, direct compression of a single crystal to 2.1 GPa does not result in a phase transition. A density decrease of 18.2% over the 0.0–2.1 GPa pressure range is observed and the principal effect of pressure is to `tighten' the herringbone structural motif and decrease the size of void regions. A new polymorph of pyrene, form III, has been crystallized at 0.3 and at 0.5 GPa. Structural investigation of this new polymorph by means of topological analysis and comparison of Hirshfeld surfaces and fingerprint plots shows that intermolecular interactions are substantially different from those found in the ambient-pressure structures, and do not fit a previously established packing model for PAHs. Similar discrepancies are found for the high-pressure polymorph of phenanthrene, which is here re-investigated in greater detail. The structures of these high-pressure polymorphs are dominated by π⋯π stacking with a limited contribution from C—H⋯π (peripheral) interactions. It is perhaps not surprising that high-pressure polymorphs deviate from a model that has been devised for ambient-pressure structures, and this may be a direct consequence of the ability of pressure to modify and combine intermolecular interactions in ways that are not usually found at ambient pressure. This is achieved by modifying the relative orientations of molecules and by encouraging the formation of denser structures in which molecules pack together more efficiently. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Fabbiani, F.P.A. Allan, D.R. Parsons, S. Pulham, C.R. 2006-10-01 doi:10.1107/S0108768106026814 International Union of Crystallography Recrystallization from a dichloromethane solution at 0.5 GPa affords new polymorphs of phenanthrene and pyrene. Structural analysis of the high-pressure polymorphs of pyrene and phenanthrene shows that intermolecular interactions are substantially different from those found in the ambient-pressure structures and do not fit a previously established packing model for polycyclic aromatic hydrocarbons. Recrystallization of naphthalene from a dichloromethane solution in the 0.2–0.6 GPa pressure range does not result in the formation of a new polymorph, and its crystal structure is reported to be stable to compression to 2.1 GPa. en HIGH-PRESSURE BEHAVIOUR; POLYCYCLIC AROMATIC HYDROCARBONS The structural response of three members of the family of polycyclic aromatic hydrocarbons (PAHs) to high-pressure recrystallization from dichloromethane solutions is presented. Recrystallization of naphthalene in the 0.2–0.6 GPa pressure range does not result in the formation of a new polymorph. Furthermore, direct compression of a single crystal to 2.1 GPa does not result in a phase transition. A density decrease of 18.2% over the 0.0–2.1 GPa pressure range is observed and the principal effect of pressure is to `tighten' the herringbone structural motif and decrease the size of void regions. A new polymorph of pyrene, form III, has been crystallized at 0.3 and at 0.5 GPa. Structural investigation of this new polymorph by means of topological analysis and comparison of Hirshfeld surfaces and fingerprint plots shows that intermolecular interactions are substantially different from those found in the ambient-pressure structures, and do not fit a previously established packing model for PAHs. Similar discrepancies are found for the high-pressure polymorph of phenanthrene, which is here re-investigated in greater detail. The structures of these high-pressure polymorphs are dominated by π⋯π stacking with a limited contribution from C—H⋯π (peripheral) interactions. It is perhaps not surprising that high-pressure polymorphs deviate from a model that has been devised for ambient-pressure structures, and this may be a direct consequence of the ability of pressure to modify and combine intermolecular interactions in ways that are not usually found at ambient pressure. This is achieved by modifying the relative orientations of molecules and by encouraging the formation of denser structures in which molecules pack together more efficiently. text/html Exploration of the high-pressure behaviour of polycyclic aromatic hydrocarbons: naphthalene, phenanthrene and pyrene text 62 5 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-10-01 826 research papers 0108-7681 med@iucr.org 842 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bm5034 The structures of both known forms of the polymorphic material ortho-acetamidobenzamide, C9H10N2O2, have been determined by low-temperature neutron single-crystal diffraction. Neutron diffraction allows the full description of the H-atom positions in this molecular material, which is vital in benchmarking related crystal-structure predictions. Significant conformational differences are indicated by a number of the torsion angles involving H atoms when compared with previous X-ray studies. A comprehensive description of the hydrogen-bonding scheme in both polymorphs is given. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Leech, C.K. Barnett, S.A. Shankland, K. Gutmann, M. Wilson, C.C. 2006-10-01 doi:10.1107/S0108768106025821 International Union of Crystallography The structures of both known forms of the polymorphic material ortho-acetamidobenzamide have been determined by low-temperature neutron single-crystal diffraction. en SINGLE-CRYSTAL NEUTRON DIFFRACTION; ACCURATE MOLECULAR STRUCTURES; HYDROGEN BONDING; POLYMORPHISM The structures of both known forms of the polymorphic material ortho-acetamidobenzamide, C9H10N2O2, have been determined by low-temperature neutron single-crystal diffraction. Neutron diffraction allows the full description of the H-atom positions in this molecular material, which is vital in benchmarking related crystal-structure predictions. Significant conformational differences are indicated by a number of the torsion angles involving H atoms when compared with previous X-ray studies. A comprehensive description of the hydrogen-bonding scheme in both polymorphs is given. text/html Accurate molecular structures and hydrogen bonding in two polymorphs of ortho-acetamidobenzamide by single-crystal neutron diffraction text 62 5 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-10-01 926 research papers 0108-7681 med@iucr.org 930 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bs5032 The positions of pairs of independent molecules in Z′ = 2 structures have been surveyed for six of the most populated space groups for that class of structure. These results have been compared with the Z′ = 1 situation to reveal whether there are any fundamental differences in the construction of the asymmetric units in these cases. The results indicate that, broadly speaking, the packing of the molecular pairs in Z′ = 2 structures resembles that of single molecules in structures with Z′ = 1; this similarity may be chiefly attributed to the constraints imposed by the symmetry operators of the space group. However, there are key differences, which are particularly marked in the space groups with higher symmetry, that indicate that the asymmetric units in Z′ = 1 and Z′ = 2 structures are not directly comparable. In those cases where the positions of the pair centroids in Z′ = 2 structures are similar to the positions of molecular centroids for Z′ = 1 structures, it follows that the molecular centroids in Z′ = 2 structures must follow a different distribution. A different pattern is produced if the independent molecules in Z′ = 2 structures behave like the individual molecules in Z′ = 1 structures. These two scenarios combine to form the observed distributions of pair centroid positions. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Collins, A. 2006-10-01 doi:10.1107/S0108768106025195 International Union of Crystallography The positions of molecular pairs in structures with Z′ = 2 are considered for space groups common for that class of structure in the Cambridge Structural Database. en Z' = 2; PACKING PATTERNS The positions of pairs of independent molecules in Z′ = 2 structures have been surveyed for six of the most populated space groups for that class of structure. These results have been compared with the Z′ = 1 situation to reveal whether there are any fundamental differences in the construction of the asymmetric units in these cases. The results indicate that, broadly speaking, the packing of the molecular pairs in Z′ = 2 structures resembles that of single molecules in structures with Z′ = 1; this similarity may be chiefly attributed to the constraints imposed by the symmetry operators of the space group. However, there are key differences, which are particularly marked in the space groups with higher symmetry, that indicate that the asymmetric units in Z′ = 1 and Z′ = 2 structures are not directly comparable. In those cases where the positions of the pair centroids in Z′ = 2 structures are similar to the positions of molecular centroids for Z′ = 1 structures, it follows that the molecular centroids in Z′ = 2 structures must follow a different distribution. A different pattern is produced if the independent molecules in Z′ = 2 structures behave like the individual molecules in Z′ = 1 structures. These two scenarios combine to form the observed distributions of pair centroid positions. text/html Distribution of molecular pairs in Z′ = 2 structures text 62 5 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-10-01 897 research papers 0108-7681 med@iucr.org 911 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bs5034 The geometry of hydrogen bonds in 1,6-anhydro-β-d-glucopyranose (levoglucosan) is accurately determined by refinement of time-of-flight neutron single-crystal diffraction data. Molecules of levoglucosan are held together by a hydrogen-bond array formed by a combination of strong O—H⋯O and supporting weaker C—H⋯O bonds. These are fully and accurately detailed by the neutron diffraction study. The strong hydrogen bonds link molecules in finite chains, with hydroxyl O atoms acting as both donors and acceptors of hydroxyl H atoms. A comparison of molecular and solid-state DFT calculations predicts red shifts of O—H and associated blue shifts of C—H stretching frequencies due to the formation of hydrogen bonds in this system. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Smrčok, Ľ. Sládkovičová, M. Langer, V. Wilson, C.C. Koóš, M. 2006-10-01 doi:10.1107/S010876810602489X International Union of Crystallography The geometry of hydrogen bonds in 1,6-anhydro-β-d-glucopyranose is accurately determined by single-crystal neutron diffraction. DFT calculations predict red (blue) shifts of stretching frequencies of O—H (C—H) in this material due to the formation of hydrogen bonds. en HYDROGEN BONDING; NEUTRON DIFFRACTION; DFT; LEVOGLUCOSAN The geometry of hydrogen bonds in 1,6-anhydro-β-d-glucopyranose (levoglucosan) is accurately determined by refinement of time-of-flight neutron single-crystal diffraction data. Molecules of levoglucosan are held together by a hydrogen-bond array formed by a combination of strong O—H⋯O and supporting weaker C—H⋯O bonds. These are fully and accurately detailed by the neutron diffraction study. The strong hydrogen bonds link molecules in finite chains, with hydroxyl O atoms acting as both donors and acceptors of hydroxyl H atoms. A comparison of molecular and solid-state DFT calculations predicts red shifts of O—H and associated blue shifts of C—H stretching frequencies due to the formation of hydrogen bonds in this system. text/html On hydrogen bonding in 1,6-anhydro-β-d-glucopyranose (levoglucosan): X-ray and neutron diffraction and DFT study text 62 5 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-10-01 912 research papers 0108-7681 med@iucr.org 918 1600-5740 http://scripts.iucr.org/cgi-bin/paper?gp5012 The behaviour of the Flack parameter for centrosymmetric and pseudo-centrosymmetric crystal structures based on crystal structures published as being non-centrosymmetric is presented. It is confirmed for centrosymmetric structures that the value obtained for the Flack parameter is critically dependent on the Friedel coverage of the intensity data, approaching 0.5 for a coverage of 100% and sticking near the starting value for a coverage of 0%. For pseudo-centrosymmetric structures, even those very close to being centrosymmetric, it is found that it is often possible to obtain significant values of the Flack parameter. A theoretical basis for this surprising result is established. It has also been possible to establish an a priori estimate of the standard uncertainty of the Flack parameter based only on the chemical composition of the compound and the wavelength of the radiation. The paper concludes with preliminary presentations of bias in the Flack parameter and of inconsistent chemical and crystallographic data. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Flack, H.D. Bernardinelli, G. Clemente, D.A. Linden, A. Spek, A.L. 2006-10-01 doi:10.1107/S0108768106021884 International Union of Crystallography An analysis of the Flack parameter based on published (pseudo-)centrosymmetric crystal-structure determinations. en FLACK PARAMETER; CENTROSYMMETRIC; NON-CENTROSYMMETRIC; PSEUDO-CENTROSYMMETRIC The behaviour of the Flack parameter for centrosymmetric and pseudo-centrosymmetric crystal structures based on crystal structures published as being non-centrosymmetric is presented. It is confirmed for centrosymmetric structures that the value obtained for the Flack parameter is critically dependent on the Friedel coverage of the intensity data, approaching 0.5 for a coverage of 100% and sticking near the starting value for a coverage of 0%. For pseudo-centrosymmetric structures, even those very close to being centrosymmetric, it is found that it is often possible to obtain significant values of the Flack parameter. A theoretical basis for this surprising result is established. It has also been possible to establish an a priori estimate of the standard uncertainty of the Flack parameter based only on the chemical composition of the compound and the wavelength of the radiation. The paper concludes with preliminary presentations of bias in the Flack parameter and of inconsistent chemical and crystallographic data. text/html Centrosymmetric and pseudo-centrosymmetric structures refined as non-centrosymmetric text 62 5 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-10-01 695 research papers 0108-7681 med@iucr.org 701 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bm5031 The crystal structures of triethyl-1,3,5-triazine-2,4,6-tricarb­oxylate (I), triethyl-1,3,5-benzenetricarboxylate (II) and tris-2-hydroxyethyl isocyanurate (III) have been determined from conventional laboratory X-ray powder diffraction data using the differential evolution structure solution technique. The determination of these structures presented an unexpectedly wide variation in levels of difficulty, with only the determination of (III) being without complication. In the case of (I) structure solution resulted in a Rietveld refinement profile that was not ideal, but was subsequently rationalized by single-crystal diffraction as resulting from disorder. Refinement of structure (II) showed significant variation in side-chain conformation from the initial powder structure solution. Further investigation showed that the structure solution optimization had indeed been successful, and that preferred orientation had a dramatic effect on the structure-solution R-factor search surface. Despite the presence of identical side chains in (I) and (II), only the triazine-based system retains threefold mol­ecular symmetry in the crystal structure. The lack of use of the heterocyclic N atom as a hydrogen-bond acceptor in this structure results in the formation of a similar non-centrosymmetric network to the benzene-based structure, but with overall three-dimensional centrosymmetry. The hydrogen-bonded layer structure of (III) is similar to that of other isocyanurate-based structures of this type. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Chong, S.Y. Seaton, C.C. Kariuki, B.M. Tremayne, M. 2006-10-01 doi:10.1107/S0108768106020921 International Union of Crystallography The crystal structures of triethyl-1,3,5-triazine-2,4,6-tricarboxylate, triethyl-1,3,5-benzenetricarboxylate and tris-2-hydroxyethyl isocyanurate have been determined from laboratory X-ray powder and single-crystal diffraction data, despite the presence of disorder and significant preferred orientation. The materials display contrasting packing behaviour, with only the triazine derivative retaining threefold molecular symmetry in its crystal structure. en MOLECULAR SYMMETRY; CRYSTAL SYMMETRY; X-RAY POWDER DIFFRACTION; SINGLE-CRYSTAL DIFFRACTION; DISORDER; PREFERRED ORIENTATION The crystal structures of triethyl-1,3,5-triazine-2,4,6-tricarb­oxylate (I), triethyl-1,3,5-benzenetricarboxylate (II) and tris-2-hydroxyethyl isocyanurate (III) have been determined from conventional laboratory X-ray powder diffraction data using the differential evolution structure solution technique. The determination of these structures presented an unexpectedly wide variation in levels of difficulty, with only the determination of (III) being without complication. In the case of (I) structure solution resulted in a Rietveld refinement profile that was not ideal, but was subsequently rationalized by single-crystal diffraction as resulting from disorder. Refinement of structure (II) showed significant variation in side-chain conformation from the initial powder structure solution. Further investigation showed that the structure solution optimization had indeed been successful, and that preferred orientation had a dramatic effect on the structure-solution R-factor search surface. Despite the presence of identical side chains in (I) and (II), only the triazine-based system retains threefold mol­ecular symmetry in the crystal structure. The lack of use of the heterocyclic N atom as a hydrogen-bond acceptor in this structure results in the formation of a similar non-centrosymmetric network to the benzene-based structure, but with overall three-dimensional centrosymmetry. The hydrogen-bonded layer structure of (III) is similar to that of other isocyanurate-based structures of this type. text/html Molecular versus crystal symmetry in tri-substituted triazine, benzene and isocyanurate derivatives text 62 5 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-10-01 864 research papers 0108-7681 med@iucr.org 874 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bs5027 The hydrostatic compression of l-serine-d7 has been studied to 8.1 GPa by neutron powder diffraction. Over the course of this pressure range the compound undergoes two phase transitions, the first between 4.6 and 5.2 GPa, yielding l-serine-II, and the second between 7.3 and 8.1 GPa, yielding l-serine-III. All three polymorphs are orthorhombic, P212121, and feature chains of serine molecules connected via head-to-tail ND⋯O hydrogen bonds formed between ammonium and carboxylate groups. The chains are linked into a ribbon by a second set of ND⋯O hydrogen bonds. The hydroxyl moieties are distributed along the outer edges of the ribbon and in phase I they connect the ribbons into a layer by chains of OD⋯OD hydrogen bonds. The layers are connected together by a third set of ND⋯O hydrogen bonds, forming R^3_4(14) rings with substantial voids at their centres. In the transition from phase I to II these voids begin to close up, but at the cost of breaking the OD⋯OD chains. The OD⋯OD hydrogen bonds are replaced by shorter OD⋯O hydrogen bonds to carboxylate groups. At 7.3 GPa the O⋯O distance in the OD⋯O hydrogen bonds measures only 2.516 (17) Å, which is short, and we propose that the phase transition to phase III that occurs between 7.3 and 8.1 GPa relieves the strain that has built up in this region of the structure. The hydroxyl D atom now bifurcates between the OD⋯O contact that had been present in phase II and a new OD⋯O contact formed to a carboxylate in another layer. Hirshfeld surface fingerprint plots show that D⋯D interactions become more numerous, while hydrogen bonds actually begin to lengthen in the transition from phase II to III. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Moggach, S.A. Marshall, W.G. Parsons, S. 2006-10-01 doi:10.1107/S010876810601799X International Union of Crystallography The hydrostatic compression of l-serine-d7 has been studied to 8.1 GPa by neutron powder diffraction. Over the course of this pressure range the compound undergoes two phase transitions, the first between 4.6 and 5.2 GPa, and the second between 7.3 and 8.1 GPa. en NEUTRON POWDER DIFFRACTION; HYDROSTATIC COMPRESSION; HYDROGEN BONDING The hydrostatic compression of l-serine-d7 has been studied to 8.1 GPa by neutron powder diffraction. Over the course of this pressure range the compound undergoes two phase transitions, the first between 4.6 and 5.2 GPa, yielding l-serine-II, and the second between 7.3 and 8.1 GPa, yielding l-serine-III. All three polymorphs are orthorhombic, P212121, and feature chains of serine molecules connected via head-to-tail ND⋯O hydrogen bonds formed between ammonium and carboxylate groups. The chains are linked into a ribbon by a second set of ND⋯O hydrogen bonds. The hydroxyl moieties are distributed along the outer edges of the ribbon and in phase I they connect the ribbons into a layer by chains of OD⋯OD hydrogen bonds. The layers are connected together by a third set of ND⋯O hydrogen bonds, forming R^3_4(14) rings with substantial voids at their centres. In the transition from phase I to II these voids begin to close up, but at the cost of breaking the OD⋯OD chains. The OD⋯OD hydrogen bonds are replaced by shorter OD⋯O hydrogen bonds to carboxylate groups. At 7.3 GPa the O⋯O distance in the OD⋯O hydrogen bonds measures only 2.516 (17) Å, which is short, and we propose that the phase transition to phase III that occurs between 7.3 and 8.1 GPa relieves the strain that has built up in this region of the structure. The hydroxyl D atom now bifurcates between the OD⋯O contact that had been present in phase II and a new OD⋯O contact formed to a carboxylate in another layer. Hirshfeld surface fingerprint plots show that D⋯D interactions become more numerous, while hydrogen bonds actually begin to lengthen in the transition from phase II to III. text/html High-pressure neutron diffraction study of l-serine-I and l-serine-II, and the structure of l-serine-III at 8.1 GPa text 62 5 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-10-01 815 research papers 0108-7681 med@iucr.org 825 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bs5029 Reassessment of the reported single-crystal X-ray diffraction characterization of polymorphs of furosemide and finasteride shows that, in each case, incomplete data collections have resulted in the mistaken identification of two forms that are, in fact, identical. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Karami, S. Li, Y. Hughes, D.S. Hursthouse, M.B. Russell, A.E. Threlfall, T.L. Claybourn, M. Roberts, R. 2006-08-01 doi:10.1107/S0108768106016211 International Union of Crystallography Reassessment of the reported single-crystal X-ray diffraction characterization of polymorphs of furosemide and finasteride shows that, in each case, incomplete data collections have resulted in the mistaken identification of two forms that are, in fact, identical. en FUROSEMIDE; FINASTERIDE; POLYMORPHS Reassessment of the reported single-crystal X-ray diffraction characterization of polymorphs of furosemide and finasteride shows that, in each case, incomplete data collections have resulted in the mistaken identification of two forms that are, in fact, identical. text/html Further errors in polymorph identification: furosemide and finasteride text 62 4 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-08-01 689 short communications 0108-7681 med@iucr.org 691 1600-5740 http://scripts.iucr.org/cgi-bin/paper?ws5038 The crystal structure of phase II of tertiary butyl alcohol (2-methyl-2-propanol, C4H10O) has been solved using a combination of single-crystal X-ray diffraction techniques and ab initio density functional calculations. This trigonal P\overline 3 phase, which is stable at both low temperature and high pressure, and the triclinic P\overline 1 phase (phase IV) have very similar enthalpies, the calculations revealing only a 3.859 kJ mol−1 enthalpy difference at ambient pressure, despite the substantial change of the intermolecular bonding motif from helical catemer to hexamer with an increase in pressure or reduction in temperature. The hexamers in the trigonal phase adopt a chair conformation. There are two unique hexamers: at low temperature these are centred at (0, 0, 1\over2) and (2\over3, 1\over3, 0.961 (13)), and at high pressure the centres are (0, 0, 1\over2) and (2\over3, 1\over3, 0.958 (14)). A slight flattening of the hexamers is observed at high pressure and the calculations confirm that phase II becomes more stable relative to phase IV on pressure increase. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 McGregor, P.A. Allan, D.R. Parsons, S. Clark, S.J. 2006-08-01 doi:10.1107/S0108768106015424 International Union of Crystallography The crystal structure of phase II of tertiary butyl alcohol (2-methyl-2-propanol) has been solved using a combination of single-crystal X-ray diffraction techniques and ab initio density functional calculations. The calculations indicate that the trigonal P\bar 3 phase II structure is slightly more stable at elevated pressure than that of the triclinic P\bar 1 phase IV. en HEXAMER FORMATION; 2-METHYL-2-PROPANOL The crystal structure of phase II of tertiary butyl alcohol (2-methyl-2-propanol, C4H10O) has been solved using a combination of single-crystal X-ray diffraction techniques and ab initio density functional calculations. This trigonal P\overline 3 phase, which is stable at both low temperature and high pressure, and the triclinic P\overline 1 phase (phase IV) have very similar enthalpies, the calculations revealing only a 3.859 kJ mol−1 enthalpy difference at ambient pressure, despite the substantial change of the intermolecular bonding motif from helical catemer to hexamer with an increase in pressure or reduction in temperature. The hexamers in the trigonal phase adopt a chair conformation. There are two unique hexamers: at low temperature these are centred at (0, 0, 1\over2) and (2\over3, 1\over3, 0.961 (13)), and at high pressure the centres are (0, 0, 1\over2) and (2\over3, 1\over3, 0.958 (14)). A slight flattening of the hexamers is observed at high pressure and the calculations confirm that phase II becomes more stable relative to phase IV on pressure increase. text/html Hexamer formation in tertiary butyl alcohol (2-methyl-2-propanol, C4H10O) text 62 4 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-08-01 599 research papers 0108-7681 med@iucr.org 605 1600-5740 http://scripts.iucr.org/cgi-bin/paper?ws5035 The crystallography and microwave dielectric properties of La(Zn1/2Ti1/2)O3 (LZT) ceramics prepared via the mixed-oxide route were investigated in this study. While samples were largely single phase, small amounts of ZnO impurity were detected in sintered pellets. Observed reflections in electron and neutron diffraction patterns indicate that the symmetry of LZT is P21/n. The B site is ordered on {110} or pseudocubic {111}, but the presence of the pseudocubic 1\over2(111) reflection is in itself insufficient to indicate the existence of such order. Rietveld refinements of the neutron diffraction data yield an excellent fit for such a model. The structure is highly twinned, with variants related through common {211} composition planes and 90° rotations about 〈011〉. The microwave dielectric properties measured were ∊r = 34, Qf = 36 090 and τf = −70 MK−1. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Ubic, R. Hu, Y. Abrahams, I. 2006-08-01 doi:10.1107/S0108768106015527 International Union of Crystallography The structure of the perovskite compound La(Zn1/2Ti1/2)O3 is monoclinic, space group P21/n. The B site is ordered on {110}, but the presence of the pseudocubic 1\over2(111) reflection is insufficient by itself to indicate the existence of such order. en PEROVSKITE; NEUTRON DIFFRACTION; ELECTRON DIFFRACTION; MICROWAVE DIELECTRIC The crystallography and microwave dielectric properties of La(Zn1/2Ti1/2)O3 (LZT) ceramics prepared via the mixed-oxide route were investigated in this study. While samples were largely single phase, small amounts of ZnO impurity were detected in sintered pellets. Observed reflections in electron and neutron diffraction patterns indicate that the symmetry of LZT is P21/n. The B site is ordered on {110} or pseudocubic {111}, but the presence of the pseudocubic 1\over2(111) reflection is in itself insufficient to indicate the existence of such order. Rietveld refinements of the neutron diffraction data yield an excellent fit for such a model. The structure is highly twinned, with variants related through common {211} composition planes and 90° rotations about 〈011〉. The microwave dielectric properties measured were ∊r = 34, Qf = 36 090 and τf = −70 MK−1. text/html Neutron and electron diffraction studies of La(Zn1/2Ti1/2)O3 perovskite text 62 4 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-08-01 521 research papers 0108-7681 med@iucr.org 529 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bm5033 Structures are reported here for eight further substituted N-aryl-2-chloronicotinamides, 2-ClC5H3NCONHC6H4X-4′. When X = H, compound (I) (C12H9ClN2O), the molecules are linked into sheets by N—H⋯N, C—H⋯π(pyridyl) and C—H⋯π(arene) hydrogen bonds. For X = CH3, compound (II) (C13H11ClN2O, triclinic P\bar 1 with Z′ = 2), the molecules are linked into sheets by N—H⋯O, C—H⋯O and C—H⋯π(arene) hydrogen bonds. Compound (III), where X = F, crystallizes as a monohydrate (C12H8ClFN2O·H2O) and sheets are formed by N—H⋯O, O—H⋯O and O—H⋯N hydrogen bonds and aromatic π⋯π stacking interactions. Crystals of compound (IV), where X = Cl (C12H8Cl2N2O, monoclinic P21 with Z′ = 4) exhibit inversion twinning: the molecules are linked by N—H⋯O hydrogen bonds into four independent chains, linked in pairs by C—H⋯π(arene) hydrogen bonds. When X = Br, compound (V) (C12H8BrClN2O), the molecules are linked into sheets by N—H⋯O and C—H⋯N hydrogen bonds, while in compound (VI), where X = I (C12H8ClIN2O), the molecules are linked into a three-dimensional framework by N—H⋯O and C—H⋯π(arene) hydrogen bonds and an iodo⋯N(pyridyl) interaction. For X = CH3O, compound (VII) (C13H11ClN2O2), the molecules are linked into chains by a single N—H⋯O hydrogen bond. Compound (VIII) (C13H8ClN3O, triclinic P\bar 1 with Z′ = 2), where X = CN, forms a complex three-dimensional framework by N—H⋯N, C—H⋯N and C—H⋯O hydrogen bonds and two independent aromatic π⋯π stacking interactions. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Cuffini, S. Glidewell, C. Low, J.N. de Oliveira, A.G. de Souza, M.V.N. Vasconcelos, T.R.A. Wardell, S.M.S.V. Wardell, J.L. 2006-08-01 doi:10.1107/S0108768106015497 International Union of Crystallography Substituted N-aryl-2-chloronicotinamides, 2-ClC5H3NCONHC6H4X-4′, can have supramolecular structures which are one-, two- or three-dimensional, and are all built from different combinations of direction-specific intermolecular interactions. en SUPRAMOLECULAR STRUCTURES; DIRECTION-SPECIFIC INTERMOLECULAR INTERACTIONS; HYDROGEN BONDS; VITAMIN B Structures are reported here for eight further substituted N-aryl-2-chloronicotinamides, 2-ClC5H3NCONHC6H4X-4′. When X = H, compound (I) (C12H9ClN2O), the molecules are linked into sheets by N—H⋯N, C—H⋯π(pyridyl) and C—H⋯π(arene) hydrogen bonds. For X = CH3, compound (II) (C13H11ClN2O, triclinic P\bar 1 with Z′ = 2), the molecules are linked into sheets by N—H⋯O, C—H⋯O and C—H⋯π(arene) hydrogen bonds. Compound (III), where X = F, crystallizes as a monohydrate (C12H8ClFN2O·H2O) and sheets are formed by N—H⋯O, O—H⋯O and O—H⋯N hydrogen bonds and aromatic π⋯π stacking interactions. Crystals of compound (IV), where X = Cl (C12H8Cl2N2O, monoclinic P21 with Z′ = 4) exhibit inversion twinning: the molecules are linked by N—H⋯O hydrogen bonds into four independent chains, linked in pairs by C—H⋯π(arene) hydrogen bonds. When X = Br, compound (V) (C12H8BrClN2O), the molecules are linked into sheets by N—H⋯O and C—H⋯N hydrogen bonds, while in compound (VI), where X = I (C12H8ClIN2O), the molecules are linked into a three-dimensional framework by N—H⋯O and C—H⋯π(arene) hydrogen bonds and an iodo⋯N(pyridyl) interaction. For X = CH3O, compound (VII) (C13H11ClN2O2), the molecules are linked into chains by a single N—H⋯O hydrogen bond. Compound (VIII) (C13H8ClN3O, triclinic P\bar 1 with Z′ = 2), where X = CN, forms a complex three-dimensional framework by N—H⋯N, C—H⋯N and C—H⋯O hydrogen bonds and two independent aromatic π⋯π stacking interactions. text/html Nine N-aryl-2-chloronicotinamides: supramolecular structures in one, two and three dimensions text 62 4 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-08-01 651 research papers 0108-7681 med@iucr.org 665 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bm5032 The structures of five of the possible six isomers of (E,E)-1,4-bis(nitrophenyl)-2,3-diaza-1,3-butadiene are reported, including two polymorphs of one of the isomers. (E,E)-1,4-Bis(2-nitrophenyl)-2,3-diaza-1,3-butadiene, C14H10N4O4 (I), crystallizes in two polymorphic forms (Ia) and (Ib) in which the molecules lie across centres of inversion in space groups P21/n and P21/c, respectively: the molecules in (Ia) and (Ib) are linked into chains by aromatic π⋯π stacking interactions and C—H⋯π(arene) hydrogen bonds, respectively. Molecules of (E,E)-1-(2-nitrophenyl)-4-(3-nitrophenyl)-2,3-diaza-1,3-butadiene (II) are linked into sheets by two independent C—H⋯O hydrogen bonds. The molecules of (E,E)-1,4-bis(3-nitrophenyl)-2,3-diaza-1,3-butadiene (III) lie across inversion centres in the space group P21/n, and a combination of a C—H⋯O hydrogen bond and a π⋯π stacking interaction links the molecules into sheets. A total of four independent C—H⋯O hydrogen bonds link the molecules of (E,E)-1-(3-nitrophenyl)-4-(4-nitrophenyl)-2,3-diaza-1,3-butadiene (IV) into sheets. In (E,E)-1,4-bis(4-nitrophenyl)-2,3-diaza-1,3-butadiene (V) the molecules, which lie across centres of inversion in the space group P21/n, are linked by just two independent C—H⋯O hydrogen bonds into a three-dimensional framework. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Glidewell, C. Low, J.N. Skakle, J.M.S. Wardell, J.L. 2006-08-01 doi:10.1107/S010876810601439X International Union of Crystallography Five isomeric (E,E)-1,4-bis(nitrophenyl)-2,3-diaza-1,3-butadienes all display different direction-specific intermolecular interactions and all give different supramolecular structures. en SUPRAMOLECULAR STRUCTURES; DIRECTION-SPECIFIC INTERMOLECULAR INTERACTIONS; POLYMORPHISM; HYDROGEN BONDING The structures of five of the possible six isomers of (E,E)-1,4-bis(nitrophenyl)-2,3-diaza-1,3-butadiene are reported, including two polymorphs of one of the isomers. (E,E)-1,4-Bis(2-nitrophenyl)-2,3-diaza-1,3-butadiene, C14H10N4O4 (I), crystallizes in two polymorphic forms (Ia) and (Ib) in which the molecules lie across centres of inversion in space groups P21/n and P21/c, respectively: the molecules in (Ia) and (Ib) are linked into chains by aromatic π⋯π stacking interactions and C—H⋯π(arene) hydrogen bonds, respectively. Molecules of (E,E)-1-(2-nitrophenyl)-4-(3-nitrophenyl)-2,3-diaza-1,3-butadiene (II) are linked into sheets by two independent C—H⋯O hydrogen bonds. The molecules of (E,E)-1,4-bis(3-nitrophenyl)-2,3-diaza-1,3-butadiene (III) lie across inversion centres in the space group P21/n, and a combination of a C—H⋯O hydrogen bond and a π⋯π stacking interaction links the molecules into sheets. A total of four independent C—H⋯O hydrogen bonds link the molecules of (E,E)-1-(3-nitrophenyl)-4-(4-nitrophenyl)-2,3-diaza-1,3-butadiene (IV) into sheets. In (E,E)-1,4-bis(4-nitrophenyl)-2,3-diaza-1,3-butadiene (V) the molecules, which lie across centres of inversion in the space group P21/n, are linked by just two independent C—H⋯O hydrogen bonds into a three-dimensional framework. text/html Isomers and polymorphs of (E,E)-1,4-bis(nitrophenyl)-2,3-diaza-1,3-butadienes text 62 4 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-08-01 666 research papers 0108-7681 med@iucr.org 675 1600-5740 http://scripts.iucr.org/cgi-bin/paper?av5050 The crystal structures of the four-membered heterocycles (S)-(−)-4-oxo-2-azetidinecarboxylic acid (I) and 3-azetidinecarboxylic acid (II) were solved by direct methods using powder synchrotron X-ray diffraction data. The asymmetry of the oxoazetidine and azetidine rings is discussed, along with the hydrogen bonding. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Mora, A.J. Brunelli, M. Fitch, A.N. Wright, J. Báez, M.E. López-Carrasquero, F. 2006-08-01 doi:10.1107/S0108768106013887 International Union of Crystallography The crystal structures of the four-membered heterocycles (S)-(−)-4-oxo-2-azetidinecarboxylic acid and 3-azetidinecarboxylic acid were solved by direct methods using powder synchrotron X-ray diffraction data. en POWDER DIFFRACTION; STRUCTURAL SOLUTION; HETEROCYCLES; ANTIBIOTICS; ASYMMETRY; HYDROGEN BONDING The crystal structures of the four-membered heterocycles (S)-(−)-4-oxo-2-azetidinecarboxylic acid (I) and 3-azetidinecarboxylic acid (II) were solved by direct methods using powder synchrotron X-ray diffraction data. The asymmetry of the oxoazetidine and azetidine rings is discussed, along with the hydrogen bonding. text/html Structures of (S)-(−)-4-oxo-2-azetidinecarboxylic acid and 3-azetidinecarboxylic acid from powder synchrotron diffraction data text 62 4 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-08-01 606 research papers 0108-7681 med@iucr.org 611 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bk5029 The commercially available peptide coupling reagent 1-hydroxy-7-azabenzotriazole has been shown to crystallize in two polymorphic forms. The two polymorphs differ in their hydrogen-bonding motif, with form I having an R_2^2(10) dimer motif and form II having a C(5) chain motif. The previously unreported form II was used as an informal blind test of computational crystal structure prediction for flexible molecules. The crystal structure of form II has been successfully predicted blind from lattice-energy minimization calculations following a series of searches using a large number of rigid conformers. The structure for form II was the third lowest in energy with form I found as the global minimum, with the energy calculated as the sum of the ab initio intramolecular energy penalty for conformational distortion and the intermolecular lattice energy which is calculated from a distributed multipole representation of the charge density. The predicted structure was sufficiently close to the experimental structure that it could be used as a starting model for crystal structure refinement. A subsequent limited polymorph screen failed to yield a third polymorphic form, but demonstrated that alcohol solvents are implicated in the formation of the form I dimer structure. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Nowell, H. Frampton, C.S. Waite, J. Price, S.L. 2006-08-01 doi:10.1107/S0108768106012584 International Union of Crystallography The crystal structure of a novel conformational polymorph of 1-hydroxy-7-azabenzotriazole has been independently predicted in an informal blind test. en CONFORMATIONAL POLYMORPHISM; CRYSTAL STRUCTURE PREDICTION; POLYMORPH SCREENING The commercially available peptide coupling reagent 1-hydroxy-7-azabenzotriazole has been shown to crystallize in two polymorphic forms. The two polymorphs differ in their hydrogen-bonding motif, with form I having an R_2^2(10) dimer motif and form II having a C(5) chain motif. The previously unreported form II was used as an informal blind test of computational crystal structure prediction for flexible molecules. The crystal structure of form II has been successfully predicted blind from lattice-energy minimization calculations following a series of searches using a large number of rigid conformers. The structure for form II was the third lowest in energy with form I found as the global minimum, with the energy calculated as the sum of the ab initio intramolecular energy penalty for conformational distortion and the intermolecular lattice energy which is calculated from a distributed multipole representation of the charge density. The predicted structure was sufficiently close to the experimental structure that it could be used as a starting model for crystal structure refinement. A subsequent limited polymorph screen failed to yield a third polymorphic form, but demonstrated that alcohol solvents are implicated in the formation of the form I dimer structure. text/html Blind crystal structure prediction of a novel second polymorph of 1-hydroxy-7-azabenzotriazole text 62 4 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-08-01 642 research papers 0108-7681 med@iucr.org 650 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bk5025 The structures of two neutral and 17 salt forms of the base (1R, 2S)-(−)-ephedrine are reported. These structures are discussed in the light of the conformers of the ephedrine moiety, the existence of bilayers and the structure determining role of the counterions. Overall, most of the salt structures are essentially derived from the observed packing of the neutral base and are dominated by the amphiphilic nature of the ephedrine molecular structure. In a few cases the size and hydrophobicity of the counterion disrupts this behaviour. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Collier, E.A. Davey, R.J. Black, S.N. Roberts, R.J. 2006-06-01 doi:10.1107/S0108768106012018 International Union of Crystallography The structures of anhydrous ephedrine and ephedrine hemihydrate together with 17 salts of the base are reported. It is evident that the observed packings are in most cases related to those of the neutral molecule, incorporating both bilayer and conformational elements. en PACKING ANALYSIS; COUNTERION; MOLECULAR SALTS; PHARMACEUTICALS The structures of two neutral and 17 salt forms of the base (1R, 2S)-(−)-ephedrine are reported. These structures are discussed in the light of the conformers of the ephedrine moiety, the existence of bilayers and the structure determining role of the counterions. Overall, most of the salt structures are essentially derived from the observed packing of the neutral base and are dominated by the amphiphilic nature of the ephedrine molecular structure. In a few cases the size and hydrophobicity of the counterion disrupts this behaviour. text/html 17 salts of ephedrine: crystal structures and packing analysis text 62 3 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-06-01 498 research papers 0108-7681 med@iucr.org 505 1600-5740 http://scripts.iucr.org/cgi-bin/paper?so5003 The structures of four selenium analogues of the antithyroid drug 6-n-propyl-2-thiouracil [systematic name: 2,3-dihydro-6-n-propyl-2-thioxopyrimidin-4(1H)-one], namely 6-methyl-2-selenouracil, C5H6N2OSe (1), 6-ethyl-2-selenouracil, C6H8N2OSe (2), 6-n-propyl-2-selenouracil, C7H10N2OSe (3), and 6-isopropyl-2-selenouracil, C7H10N2OSe (4), are described, along with that of the dichloromethane monosolvate of 6-isopropyl-2-selenouracil, C7H10N2OSe·CH2Cl2 (4·CH2Cl2). The extended structure of (1) is a two-dimensional sheet of topology 63 with a brick-wall architecture. The extended structures of (2) and (4) are analogous, being based on a chain of eight-membered R86(32) hydrogen-bonded rings. In (3) and (4·CH2Cl2), R22(8) hydrogen bonding links molecules into chains. 6-n-Propyl-2-selenouracil·I2, C7H10N2OSe·I2 (7), is a charge-transfer complex with a `spoke' structure, the extended structure of which is based on a linear chain formed principally by intermolecular N—H⋯O hydrogen bonds. Re-crystallization of 6-ethyl-2-selenouracil or (7) from acetone gave crystals of the diselenides [N-(6′-ethyl-4′-pyr­imidone)(6-ethyl-2-selenouracil)2(Se—Se)]·2H2O (9·2H2O) or [N-(6′-n-propyl-4′-pyrimidone)(6-n-propyl-2-selenouracil)2(Se—Se)] (10), respectively: these have similar extended chain structures formed via N—H⋯O and C—H⋯O hydrogen bonds, stacked to give two-dimensional sheets. Re-crystallization of (7) from methanol/acetonitrile led via deselenation to the formation of crystals of 6-n-propyl-2-uracil (11), in which six symmetry-related molecules combine to form a six-membered R66(24) hydrogen-bonded ring, with each pair of molecules linked by an R22(8) motif. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Antoniadis, C.D. Blake, A.J. Hadjikakou, S.K. Hadjiliadis, N. Hubberstey, P. Schröder, M. Wilson, C. 2006-08-01 doi:10.1107/S0108768106011426 International Union of Crystallography The structures of selenium analogues of the antithyroid drug 6-n-propyl-2-thiouracil, the charge-transfer complex 6-n-propyl-2-selenouracil·I2, two diselenides and the deselenation product 6-n-propyl-2-uracil all show extended architectures. These are based on hydrogen-bonding and, in the case of 6-n-propyl-2-selenouracil·I2, on Se⋯I interactions. en SELENOURACIL; HYDROGEN BONDING; CHARGE-TRANSFER COMPLEX; ANTITHYROID DRUG The structures of four selenium analogues of the antithyroid drug 6-n-propyl-2-thiouracil [systematic name: 2,3-dihydro-6-n-propyl-2-thioxopyrimidin-4(1H)-one], namely 6-methyl-2-selenouracil, C5H6N2OSe (1), 6-ethyl-2-selenouracil, C6H8N2OSe (2), 6-n-propyl-2-selenouracil, C7H10N2OSe (3), and 6-isopropyl-2-selenouracil, C7H10N2OSe (4), are described, along with that of the dichloromethane monosolvate of 6-isopropyl-2-selenouracil, C7H10N2OSe·CH2Cl2 (4·CH2Cl2). The extended structure of (1) is a two-dimensional sheet of topology 63 with a brick-wall architecture. The extended structures of (2) and (4) are analogous, being based on a chain of eight-membered R86(32) hydrogen-bonded rings. In (3) and (4·CH2Cl2), R22(8) hydrogen bonding links molecules into chains. 6-n-Propyl-2-selenouracil·I2, C7H10N2OSe·I2 (7), is a charge-transfer complex with a `spoke' structure, the extended structure of which is based on a linear chain formed principally by intermolecular N—H⋯O hydrogen bonds. Re-crystallization of 6-ethyl-2-selenouracil or (7) from acetone gave crystals of the diselenides [N-(6′-ethyl-4′-pyr­imidone)(6-ethyl-2-selenouracil)2(Se—Se)]·2H2O (9·2H2O) or [N-(6′-n-propyl-4′-pyrimidone)(6-n-propyl-2-selenouracil)2(Se—Se)] (10), respectively: these have similar extended chain structures formed via N—H⋯O and C—H⋯O hydrogen bonds, stacked to give two-dimensional sheets. Re-crystallization of (7) from methanol/acetonitrile led via deselenation to the formation of crystals of 6-n-propyl-2-uracil (11), in which six symmetry-related molecules combine to form a six-membered R66(24) hydrogen-bonded ring, with each pair of molecules linked by an R22(8) motif. text/html Structural characterization of selenium and selenium-diiodine analogues of the antithyroid drug 6-n-propyl-2-thiouracil and its alkyl derivatives text 62 4 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-08-01 580 research papers 0108-7681 med@iucr.org 591 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bk0150 The first (so-called) lambda transition in solids was found in the specific heat measurements for NH4Cl at 242 K by F. Simon in 1922 [Simon (1922). Ann. Phys. 68, 241–280]. Analogous phenomena found in many other solids gave rise to doubts (expressed most clearly by A. R. Ubbelohde some 50 years ago) about the applicability of classical thermodynamics to some phase transitions [Ubbelohde (1956). Brit. J. Appl. Phys. 7, 313–321]. However, Y. Mnyukh's studies of enantiotropic phase transitions in eight organic crystals showed that all proceed by a nucleation-and-growth mechanism [summarized in Mnyukh (2001), Fundamentals of Solid State Phase Transitions, Ferromagnetism and Ferroelectricity. 1st Books]. Nucleation is localized at defects in the parent phase; growth can be epitaxic and oriented if parent and daughter phases have closely similar structures, or random (not oriented) if there are substantial structural differences. This conclusion is supported by a critical review of Mnyukh's eight examples and other results published in the interim. It seems that Ubbelohde's invocation of `hybrid crystals' and `smeared transitions' can mostly be accounted for by lack of equilibrium in the phase-transition studies cited by him. However, the intermediate phase in 4,4′-dichlorobenzophenone appears to have structural resemblances to Ubbelohde's' `hybrid crystal'. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Herbstein, F.H. 2006-06-01 doi:10.1107/S0108768106008640 International Union of Crystallography An integrated and comparative study of more than 20 enantiotropic solid-state phase transitions shows that these are all first-order and proceed by a `nucleation and growth' mechanism in accordance with the description set out especially by Yuri Mnyukh. en SOLID-STATE PHASE TRANSITIONS; POLYMORPHISM; FIRST ORDER The first (so-called) lambda transition in solids was found in the specific heat measurements for NH4Cl at 242 K by F. Simon in 1922 [Simon (1922). Ann. Phys. 68, 241–280]. Analogous phenomena found in many other solids gave rise to doubts (expressed most clearly by A. R. Ubbelohde some 50 years ago) about the applicability of classical thermodynamics to some phase transitions [Ubbelohde (1956). Brit. J. Appl. Phys. 7, 313–321]. However, Y. Mnyukh's studies of enantiotropic phase transitions in eight organic crystals showed that all proceed by a nucleation-and-growth mechanism [summarized in Mnyukh (2001), Fundamentals of Solid State Phase Transitions, Ferromagnetism and Ferroelectricity. 1st Books]. Nucleation is localized at defects in the parent phase; growth can be epitaxic and oriented if parent and daughter phases have closely similar structures, or random (not oriented) if there are substantial structural differences. This conclusion is supported by a critical review of Mnyukh's eight examples and other results published in the interim. It seems that Ubbelohde's invocation of `hybrid crystals' and `smeared transitions' can mostly be accounted for by lack of equilibrium in the phase-transition studies cited by him. However, the intermediate phase in 4,4′-dichlorobenzophenone appears to have structural resemblances to Ubbelohde's' `hybrid crystal'. text/html On the mechanism of some first-order enantiotropic solid-state phase transitions: from Simon through Ubbelohde to Mnyukh text 62 3 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-06-01 341 feature articles 0108-7681 med@iucr.org 383 1600-5740 http://scripts.iucr.org/cgi-bin/paper?pf0025 Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Lehmann, C.W. 2006-04-01 doi:10.1107/S0108768106006604 International Union of Crystallography en BOOK REVIEW text/html Crystalline Molecular Complexes and Compounds. Vol. 1 and 2. By F. H. Herbstein. Pp. xxviii + 1273. Oxford: Oxford University Press, 2005. Price (hardback) GBP 125.00. ISBN 0-19-852660-1. text 62 2 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-04-01 338 book reviews 0108-7681 med@iucr.org 339 1600-5740 http://scripts.iucr.org/cgi-bin/paper?ry5001 trans-PtCl2(dms)2 (dms is dimethyl sulfide) crystallizes in the space group P21/n and adopts the molecular point group Ci, which is the most frequently occurring point group for trans-PtX2L2 complexes (78%), as observed in the Cambridge Structural Database (CSD; 2005 release), followed by C1 (16%). Density functional theory calculations show that the observed geometry for trans-PtCl2(dms)2 has slightly higher energy than the most favorable geometry in the point group C2h, but this geometry would require a space group that hampers close packing, thus showing that intermolecular forces determine the point group for the title compound. High-pressure powder diffraction studies of trans-PtCl2(dms)2 show no phase transformation up to 8.0 GPa. The bulk modulus is 8.1 (6) GPa and the pressure derivative 8.1 (4). In the CSD, the number of cis- and trans-PtX2L2 compounds are almost equal, viz. 156 cis and 160 trans compounds, showing no preference for either isomer in the solid state. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Hansson, C. Carlson, S. Giveen, D. Johansson, M. Yong, S. Oskarsson, Å. 2006-06-01 doi:10.1107/S0108768106004629 International Union of Crystallography The crystal structure of trans-PtCl2(dms)2 (dms is dimethyl sulfide) has been determined from single-crystal diffraction data and the pressure dependence of its unit-cell dimensions has been studied with diamond–anvil cells up to 8.0 GPa using powder diffraction. trans-PtCl2(dms)2 adopts the molecular point group Ci, which is the most frequently occurring point group for trans-PtX2L2 complexes (78%) as observed in the Cambridge Structural Database (CSD), followed by C1 (16%). No preference for either trans- or cis-PtX2L2 is found in the CSD. en STRUCTURAL CLASSES; HIGH PRESSURE; CIS AND TRANS ISOMERISM; PLATINUM COMPOUNDS trans-PtCl2(dms)2 (dms is dimethyl sulfide) crystallizes in the space group P21/n and adopts the molecular point group Ci, which is the most frequently occurring point group for trans-PtX2L2 complexes (78%), as observed in the Cambridge Structural Database (CSD; 2005 release), followed by C1 (16%). Density functional theory calculations show that the observed geometry for trans-PtCl2(dms)2 has slightly higher energy than the most favorable geometry in the point group C2h, but this geometry would require a space group that hampers close packing, thus showing that intermolecular forces determine the point group for the title compound. High-pressure powder diffraction studies of trans-PtCl2(dms)2 show no phase transformation up to 8.0 GPa. The bulk modulus is 8.1 (6) GPa and the pressure derivative 8.1 (4). In the CSD, the number of cis- and trans-PtX2L2 compounds are almost equal, viz. 156 cis and 160 trans compounds, showing no preference for either isomer in the solid state. text/html Cis/trans isomers of PtX2L2 (X = halogen, L = neutral ligand); the crystal structure of trans-dichlorobis(dimethyl sulfide)platinum(II) and the pressure dependence of its unit-cell dimensions text 62 3 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-06-01 474 research papers 0108-7681 med@iucr.org 479 1600-5740 http://scripts.iucr.org/cgi-bin/paper?ws5036 The crystal structures of phase I and phase II of dimethyl sulfate, (CH3O)2SO2, have been determined using complementary high-resolution neutron powder and single-crystal X-ray diffraction techniques. Below its melting point of 241 K dimethyl sulfate crystallizes in an orthorhombic structure (I) in the space group Fdd2. On cooling below ∼175 K the crystal transforms to a monoclinic structure (II) in the space group I2/a. The molecule is located on a twofold axis (Z′ = 1/2) in both structures. The phase transition is of first order with strong hysteresis. The phase transition results in changes to both the intra- and the intermolecular coordination environment. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Ibberson, R.M. Telling, M.T.F. Parsons, S. 2006-04-01 doi:10.1107/S0108768106001893 International Union of Crystallography The crystal structures of phase I and phase II of dimethyl sulfate, (CH3O)2SO2, have been determined using complementary high-resolution neutron powder and single-crystal X-ray diffraction techniques. Below its melting point of 241 K dimethyl sulfate crystallizes in an orthorhombic structure (I) in space group Fdd2, which transforms, below ∼175 K, to a monoclinic structure (II) in space group I2/a. en NEUTRON POWDER DIFFRACTION; SINGLE-CRYSTAL X-RAY DIFFRACTION; LOW-TEMPERATURE CRYSTALLOGRAPHY; PHASE TRANSITIONS; DIMETHYL SULFATE The crystal structures of phase I and phase II of dimethyl sulfate, (CH3O)2SO2, have been determined using complementary high-resolution neutron powder and single-crystal X-ray diffraction techniques. Below its melting point of 241 K dimethyl sulfate crystallizes in an orthorhombic structure (I) in the space group Fdd2. On cooling below ∼175 K the crystal transforms to a monoclinic structure (II) in the space group I2/a. The molecule is located on a twofold axis (Z′ = 1/2) in both structures. The phase transition is of first order with strong hysteresis. The phase transition results in changes to both the intra- and the intermolecular coordination environment. text/html Structure determination and phase transition behaviour of dimethyl sulfate text 62 2 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-04-01 280 research papers 0108-7681 med@iucr.org 286 1600-5740 http://scripts.iucr.org/cgi-bin/paper?de5025 A series of compounds of the N3P3Cl(6 − n)(NHBut)n family (where n = 0, 1, 2, 4 and 6) are presented, and their molecular parameters are related to trends in physical properties, which provides insight into a potential reaction mechanism for nucleophilic substitution. The crystal structures of N3P3Cl5(NHBut) and N3P3Cl2(NHBut)4 have been determined at 120 K, and those of N3P3Cl6 and N3P3Cl4(NHBut)2 have been redetermined at 120 K. These are compared with the known structure of N3P3(NHBut)6 studied at 150 K. Trends in molecular parameters [phosphazene ring, P—Cl and P—N(HBut) distances, PCl2 angles, and endo- and exocyclic phosphazene ring parameters] across the series are observed. Hydrogen-bonding motifs are identified, characterized and compared. Both the molecular and the hydrogen-bonding parameters are related to the electron distribution in bonds and the derived basicities of the cyclophosphazene series of compounds. These findings provide evidence for a proposed mechanism for nucleophilic substitution at a phosphorus site bearing a PCl(NHBut) group. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Bartlett, S.W. Coles, S.J. Davies, D.B. Hursthouse, M.B. İbişogˇlu, H. Kiliç, A. Shaw, R.A. Ün, İ. 2006-04-01 doi:10.1107/S0108768106000851 International Union of Crystallography The crystal structures of N3P3Cl5(NHBut) and N3P3Cl2(NHBut)4 have been determined at 120 K, and those of N3P3Cl6 and N3P3Cl4(NHBut)2 have been redetermined at 120 K. These are compared with the known structure of N3P3(NHBut)6, which was studied at 150 K. Molecular parameters and hydrogen-bonding motifs are discussed and compared in the light of their chemical and physical properties. en STRUCTURE-PROPERTY RELATIONSHIPS; CYCLOPHOSPHAZENES; HYDROGEN BONDING; STRUCTURAL SYSTEMATICS A series of compounds of the N3P3Cl(6 − n)(NHBut)n family (where n = 0, 1, 2, 4 and 6) are presented, and their molecular parameters are related to trends in physical properties, which provides insight into a potential reaction mechanism for nucleophilic substitution. The crystal structures of N3P3Cl5(NHBut) and N3P3Cl2(NHBut)4 have been determined at 120 K, and those of N3P3Cl6 and N3P3Cl4(NHBut)2 have been redetermined at 120 K. These are compared with the known structure of N3P3(NHBut)6 studied at 150 K. Trends in molecular parameters [phosphazene ring, P—Cl and P—N(HBut) distances, PCl2 angles, and endo- and exocyclic phosphazene ring parameters] across the series are observed. Hydrogen-bonding motifs are identified, characterized and compared. Both the molecular and the hydrogen-bonding parameters are related to the electron distribution in bonds and the derived basicities of the cyclophosphazene series of compounds. These findings provide evidence for a proposed mechanism for nucleophilic substitution at a phosphorus site bearing a PCl(NHBut) group. text/html Structural investigations of phosphorus–nitrogen compounds. 7. Relationships between physical properties, electron densities, reaction mechanisms and hydrogen-bonding motifs of N3P3Cl(6 − n)(NHBut)n derivatives text 62 2 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-04-01 321 research papers 0108-7681 med@iucr.org 329 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bs5024 The experimental charge density in the title complex has been re-examined. The original work, reported some 8 years ago [Smith et al. (1997). J. Am. Chem. Soc. 119, 5028–5034], was undertaken using a very early version of the XD software, which contained serious programming errors. A re-refinement, using the original data and a recent version of the XD software, shows that many of the unusual aspects of this earlier study are artefacts due to these programming errors. The topological properties of the newly obtained experimental density compare well with those calculated from a theoretical DFT (density-functional theory) UHF-SCF (unrestricted Hartree Fock–self-consistent field) density. This report corrects several erroneous conclusions regarding the charge density in the title complex – in particular, the highly unusual diffuse Laplacian distribution about the Ni atom, and the trifurcated bond path from the Ni atom to the alcohol oxygen donor atoms are no longer observed. An examination of a range of topological properties of the metal–ligand bonds leads to the conclusion that the Ni—N and Ni—O bonds have an intermediate character, with a significant shared interaction, but with a substantial ionic component. This new study also reveals a previously unrecognized intramolecular H⋯H interaction in the macrocyclic ligand. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Farrugia, L.J. Frampton, C.S. Howard, J.A.K. Mallinson, P.R. Peacock, R.D. Smith, G.T. Stewart, B. 2006-04-01 doi:10.1107/S0108768106000802 International Union of Crystallography The charge density in the pendant-arm macrocylic nickel(II) coordination complex [Ni(H3L)][NO3][PF6] [H3L = N,N′,N′′-tris(2-hydroxy-3-methyl butyl)-1,4,7-triazacyclononane] has been re-examined. Unusual features of this charge density, which have been previously reported, are now shown to be artefacts due to a programming error. en CHARGE DENSITY; COORDINATION COMPLEX; XD SOFTWARE; MACROCYCLIC LIGAND The experimental charge density in the title complex has been re-examined. The original work, reported some 8 years ago [Smith et al. (1997). J. Am. Chem. Soc. 119, 5028–5034], was undertaken using a very early version of the XD software, which contained serious programming errors. A re-refinement, using the original data and a recent version of the XD software, shows that many of the unusual aspects of this earlier study are artefacts due to these programming errors. The topological properties of the newly obtained experimental density compare well with those calculated from a theoretical DFT (density-functional theory) UHF-SCF (unrestricted Hartree Fock–self-consistent field) density. This report corrects several erroneous conclusions regarding the charge density in the title complex – in particular, the highly unusual diffuse Laplacian distribution about the Ni atom, and the trifurcated bond path from the Ni atom to the alcohol oxygen donor atoms are no longer observed. An examination of a range of topological properties of the metal–ligand bonds leads to the conclusion that the Ni—N and Ni—O bonds have an intermediate character, with a significant shared interaction, but with a substantial ionic component. This new study also reveals a previously unrecognized intramolecular H⋯H interaction in the macrocyclic ligand. text/html Experimental charge-density study on the nickel(II) coordination complex [Ni(H3L)][NO3][PF6] [H3L = N,N′,N′′-tris(2-hydroxy-3-methylbutyl)-1,4,7-triazacyclononane]: a reappraisal text 62 2 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-04-01 236 research papers 0108-7681 med@iucr.org 244 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bk9011 Some of the data collection details for compound (VIII) were incorrectly given in Table 1 of Godino Salido et al. (2004). The data for compound VIII in this paper were collected using synchrotron radiation at the Daresbury SRS station 9.8, λ = 0.6935 Å (Cernik et al., 1997; Clegg, 2000). The data were collected using a Bruker SMART 1K CCD diffractometer using ω rotation with narrow frames. The computer program used in the data collection was SMART (Bruker, 2001) and for cell refinement and data reduction SAINT (Bruker, 2001). Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Godino Salido, M.L. Arranz Mascarós, P. López Garzón, R. Gutiérrez Valero, M.D. Low, J.N. Gallagher, J.F. Glidewell, C. 2006-02-01 doi:10.1107/S0108768105042059 International Union of Crystallography Correction to data collection details for compound (VIII) in Acta Cryst. (2004). B60, 46–64. en PEROVSKITES; LAYERED ORDERING; OCTAHEDRAL TILTING Some of the data collection details for compound (VIII) were incorrectly given in Table 1 of Godino Salido et al. (2004). The data for compound VIII in this paper were collected using synchrotron radiation at the Daresbury SRS station 9.8, λ = 0.6935 Å (Cernik et al., 1997; Clegg, 2000). The data were collected using a Bruker SMART 1K CCD diffractometer using ω rotation with narrow frames. The computer program used in the data collection was SMART (Bruker, 2001) and for cell refinement and data reduction SAINT (Bruker, 2001). text/html Hydrated metal(II) complexes of N-(6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl) derivatives of glycine, glycylglycine, threonine, serine, valine and methionine: a monomeric complex and coordination polymers in one, two and three dimensions linked by hydrogen bonding. Corrigendum text 62 1 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-02-01 165 addenda and errata 0108-7681 med@iucr.org 165 1600-5740 http://scripts.iucr.org/cgi-bin/paper?so5001 The polymorphic phase transition of 1,2,4,5-tetrachlorobenzene (TCB) has been investigated using neutron powder diffraction and single-crystal X-ray diffraction. The diffraction experiments show a reversible phase change that occurs as a function of temperature with no apparent loss of sample quality on transition between the two phases. Neutron powder diffraction gives detailed information on the molecular structural changes and lattice parameters from 2 K to room temperature. The structure of the low-temperature form has been elucidated for the first time using single-crystal X-ray diffraction. Comparison of the α and β structures show that they are both based on the same sheet motif, with the differences between the two being very subtle, except in terms of crystal symmetry. Detailed analysis of the structures revealed the changes required for inter-conversion. A computational polymorph search showed that these two sheet structures are more thermodynamically stable than alternative herringbone-type structures. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Barnett, S.A. Broder, C.K. Shankland, K. David, W.I.F. Ibberson, R.M. Tocher, D.A. 2006-04-01 doi:10.1107/S0108768105042102 International Union of Crystallography The polymorphic phase transition of 1,2,4,5-tetrachlorobenzene (TCB) has been investigated using neutron powder diffraction and single-crystal X-ray diffraction. en TETRACHLOROBENZENE; NEUTRON POWDER DIFFRACTION; PHASE TRANSITION; SINGLE-CRYSTAL X-RAY DIFFRACTION; CRYSTAL STRUCTURE PREDICTION The polymorphic phase transition of 1,2,4,5-tetrachlorobenzene (TCB) has been investigated using neutron powder diffraction and single-crystal X-ray diffraction. The diffraction experiments show a reversible phase change that occurs as a function of temperature with no apparent loss of sample quality on transition between the two phases. Neutron powder diffraction gives detailed information on the molecular structural changes and lattice parameters from 2 K to room temperature. The structure of the low-temperature form has been elucidated for the first time using single-crystal X-ray diffraction. Comparison of the α and β structures show that they are both based on the same sheet motif, with the differences between the two being very subtle, except in terms of crystal symmetry. Detailed analysis of the structures revealed the changes required for inter-conversion. A computational polymorph search showed that these two sheet structures are more thermodynamically stable than alternative herringbone-type structures. text/html Single-crystal X-ray and neutron powder diffraction investigation of the phase transition in tetrachlorobenzene text 62 2 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-04-01 287 research papers 0108-7681 med@iucr.org 295 1600-5740 http://scripts.iucr.org/cgi-bin/paper?gp5004 The crystal structure of α-glycylglycine (α-GLYGLY) has been determined at room temperature at pressures between 1.4 and 4.7 GPa. The structure can be considered to consist of layers. The arrangement of molecules within each layer resembles the antiparallel β-sheet motif observed in proteins, except that in α-GLYGLY the motif is constructed through NH⋯O hydrogen bonds rather than covalent amide links. Compression of α-GLYGLY proceeds via the reduction in void sizes. Voids close in such a way as to decrease the distances of stabilizing interactions such as hydrogen bonds and dipolar contacts. The largest reductions in interaction distances tend to occur for those contacts which are longest at ambient pressure. These longer interactions are formed between the β-sheet-like layers, and the largest component of the strain tensor lies in the same direction. The N⋯O distance in one NH⋯O hydrogen bond measures 2.624 (9) Å at 4.7 GPa. This is very short for this kind of interaction and the crystal begins to break up above 5.4 GPa, presumably as the result of a phase transition. The changes that occur have been analysed using Hirshfeld surfaces. Changes in the appearance of these surfaces enable rapid assessment of the structural changes that occur on compression. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Moggach, S.A. Allan, D.R. Parsons, S. Sawyer, L. 2006-04-01 doi:10.1107/S0108768105042072 International Union of Crystallography The effect of pressure up to 4.7 GPa on the crystal structure of the simplest dipeptide, glycylglycine, has been investigated. The structure is built of layers resembling the β-sheets of proteins. These layers are quite robust, with the main structural effect of pressure being to compress layers together en PRESSURE EFFECTS; HIRSHFELD SURFACES; DIPEPTIDES; HYDROGEN BONDING The crystal structure of α-glycylglycine (α-GLYGLY) has been determined at room temperature at pressures between 1.4 and 4.7 GPa. The structure can be considered to consist of layers. The arrangement of molecules within each layer resembles the antiparallel β-sheet motif observed in proteins, except that in α-GLYGLY the motif is constructed through NH⋯O hydrogen bonds rather than covalent amide links. Compression of α-GLYGLY proceeds via the reduction in void sizes. Voids close in such a way as to decrease the distances of stabilizing interactions such as hydrogen bonds and dipolar contacts. The largest reductions in interaction distances tend to occur for those contacts which are longest at ambient pressure. These longer interactions are formed between the β-sheet-like layers, and the largest component of the strain tensor lies in the same direction. The N⋯O distance in one NH⋯O hydrogen bond measures 2.624 (9) Å at 4.7 GPa. This is very short for this kind of interaction and the crystal begins to break up above 5.4 GPa, presumably as the result of a phase transition. The changes that occur have been analysed using Hirshfeld surfaces. Changes in the appearance of these surfaces enable rapid assessment of the structural changes that occur on compression. text/html Effect of pressure on the crystal structure of α-glycylglycine to 4.7 GPa; application of Hirshfeld surfaces to analyse contacts on increasing pressure text 62 2 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-04-01 310 research papers 0108-7681 med@iucr.org 320 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bk5024 The crystal structures of Nd0.7Ti0.9Al0.1O3, taken to represent the ideal Nd2/3TiO3, have been elucidated from 4 to 1273 K using high-resolution neutron powder diffraction in combination with group-theoretical analysis. The room-temperature structure is monoclinic in C2/m, on a cell with a = 7.6764 (1), b = 7.6430 (1), c = 7.7114 (1) Å, β = 90.042 (2)°. Pertinent features are the layered ordering of the A-site Nd cations/vacancies along the z axis and out-of-phase tilting of the (Ti/Al)O6 octahedra around both the x and z axes. From about 750 to 1273 K, the octahedra are tilted around just one axis (x axis) perpendicular to the direction of the cation ordering, giving rise to an orthorhombic structure with space-group symmetry Cmmm. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Zhang, Z. Howard, C.J. Knight, K.S. Lumpkin, G.R. 2006-02-01 doi:10.1107/S0108768105041066 International Union of Crystallography The room-temperature structure of the cation-deficient perovskite, Nd0.7Ti0.9Al0.1O3, with layered ordering of cations/vacancies on the A-site, involves octahedral tilting around two axes. Tilting around the axis parallel to the direction of the layered cation/vacancy ordering disappears above ca 750 K, the only tilt persisting at higher temperature being about a single axis perpendicular to this direction. en CATION-DEFICIENT PEROVSKITES; OCTAHEDRAL TILTING; NEUTRON POWDER DIFFRACTION; GROUP THEORY The crystal structures of Nd0.7Ti0.9Al0.1O3, taken to represent the ideal Nd2/3TiO3, have been elucidated from 4 to 1273 K using high-resolution neutron powder diffraction in combination with group-theoretical analysis. The room-temperature structure is monoclinic in C2/m, on a cell with a = 7.6764 (1), b = 7.6430 (1), c = 7.7114 (1) Å, β = 90.042 (2)°. Pertinent features are the layered ordering of the A-site Nd cations/vacancies along the z axis and out-of-phase tilting of the (Ti/Al)O6 octahedra around both the x and z axes. From about 750 to 1273 K, the octahedra are tilted around just one axis (x axis) perpendicular to the direction of the cation ordering, giving rise to an orthorhombic structure with space-group symmetry Cmmm. text/html Structures of the cation-deficient perovskite Nd0.7Ti0.9Al0.1O3 from high-resolution neutron powder diffraction in combination with group-theoretical analysis text 62 1 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-02-01 60 research papers 0108-7681 med@iucr.org 67 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bs5023 The crystal structure of the orthorhombic phase of l-cysteine (hereafter l-cysteine-I) consists of chains of molecules linked via NH⋯O hydrogen bonds. The chains are linked into a layer by other NH⋯O hydrogen bonds, forming R_4^4(16) ring motifs. The layers are linked by further NH⋯O and disordered SH⋯S/SH⋯O interactions. The main effects of compression to 1.8 GPa are to contract voids in the middle of the R_4^4(16) rings and to reduce S⋯S distances from 3.8457 (10) to 3.450 (4) Å. The latter is at the lower limit for S⋯S distances and we suggest that strain about the S atom is responsible for the formation of a new phase of l-cysteine, l-cysteine-III, above 1.8 GPa. The phase transition is accompanied by a change in the NCCS torsion angle from ca 60 to ca −60° and small positional displacements, but with no major changes in the orientations of the molecules. The structure of l-cysteine-III contains similar R-type ring motifs to l-cysteine-I, but there are no S⋯S contacts within 3.6 Å. l-Cysteine-III was found to be stable to at least 4.2 GPa. On decompression to 1.7 GPa, another single-crystal to single-crystal phase transition formed another previously uncharacterized phase, l-cysteine-IV. This phase is not observed on increasing pressure. The structure consists of two crystallographically independent cysteine molecules in the same conformations as those found in l-cysteine-I and l-cysteine-III. The structure separates into zones with are alternately phase I-like and phase III-like. l-Cysteine-IV can therefore be thought of as an unusual example of an intermediate phase. Further decompression to ambient pressure generates l-cysteine-I. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Moggach, S.A. Allan, D.R. Clark, S.J. Gutmann, M.J. Parsons, S. Pulham, C.R. Sawyer, L. 2006-04-01 doi:10.1107/S0108768105038802 International Union of Crystallography Compression of orthorhombic l-cysteine-I, which contains molecules in the g+ conformation, leads to the formation of a new orthorhombic phase (l-cysteine-III) with the molecules in the g− conformation. Decompression of l-cysteine-III ultimately leads to l-cysteine-I, but this proceeds through an intermediate phase, l-cysteine-IV, which contains molecules in both g+ and g− conformations. en COMPRESSION; CONFORMATION; CHAIN MOLECULES; HYDROGEN BONDS The crystal structure of the orthorhombic phase of l-cysteine (hereafter l-cysteine-I) consists of chains of molecules linked via NH⋯O hydrogen bonds. The chains are linked into a layer by other NH⋯O hydrogen bonds, forming R_4^4(16) ring motifs. The layers are linked by further NH⋯O and disordered SH⋯S/SH⋯O interactions. The main effects of compression to 1.8 GPa are to contract voids in the middle of the R_4^4(16) rings and to reduce S⋯S distances from 3.8457 (10) to 3.450 (4) Å. The latter is at the lower limit for S⋯S distances and we suggest that strain about the S atom is responsible for the formation of a new phase of l-cysteine, l-cysteine-III, above 1.8 GPa. The phase transition is accompanied by a change in the NCCS torsion angle from ca 60 to ca −60° and small positional displacements, but with no major changes in the orientations of the molecules. The structure of l-cysteine-III contains similar R-type ring motifs to l-cysteine-I, but there are no S⋯S contacts within 3.6 Å. l-Cysteine-III was found to be stable to at least 4.2 GPa. On decompression to 1.7 GPa, another single-crystal to single-crystal phase transition formed another previously uncharacterized phase, l-cysteine-IV. This phase is not observed on increasing pressure. The structure consists of two crystallographically independent cysteine molecules in the same conformations as those found in l-cysteine-I and l-cysteine-III. The structure separates into zones with are alternately phase I-like and phase III-like. l-Cysteine-IV can therefore be thought of as an unusual example of an intermediate phase. Further decompression to ambient pressure generates l-cysteine-I. text/html High-pressure polymorphism in l-cysteine: the crystal structures of l-cysteine-III and l-cysteine-IV text 62 2 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-04-01 296 research papers 0108-7681 med@iucr.org 309 1600-5740 http://scripts.iucr.org/cgi-bin/paper?ws5025 The crystal structures of the title complexes were measured at several temperatures between room temperature and 100 K. Each sample shows reversible crystal-to-crystal phase transitions as the temperature is varied. The behaviour of [U(ReO4)4(TBPO)4] (I) and [Th(ReO4)4(TBPO)4] (II) (TBPO = tri-n-butylphosphine oxide) is very similar; at room temperature, crystals of (I) and (II) are isostructural, with space group I\bar 42m, and reducing the temperature to 100 K causes a lowering of the space-group symmetry to C-centred cells, space groups Cc for (I) and Cmc21 for (II). The variation of lattice symmetry of [Th(TcO4)4(TBPO)4] (III) was found to be somewhat different, with the body-centred cubic space group, I\bar 43m, occurring at 293 K, a reduction of symmetry at 230 K to the C-centred orthorhombic space group, Cmc21, and a further transition to the primitive orthorhombic space group, Pbc21, below 215 K. Elucidation of the correct space-group symmetry and the subsequent refinement was complicated in some cases by the twinning by pseudo-merohedry that arises from the lowering of the space-group symmetry, occurring as the temperature is reduced. All three of the crystal structures determined at room temperature have high atomic displacement parameters, particularly of the nBu groups, and (III) shows disorder of some of the O atoms. The structures in the space group Cmc21, show some disorder of nBu groups, but are otherwise reasonably well ordered; the structures of (I) in Cc and (III) in Pbc21 are ordered, even to the ends of the alkyl chains. Inter-comparison of the structures measured below 293 K, using the program OFIT from the SHELXTL package, showed that generally, they are remarkably alike, with weighted r.m.s. deviations of the M, M′ and P atoms of less than 0.1 Å, as are the 293 K structures of (I) and (II) with their low-temperature counterparts. However, the structure of (III) measured in the space group Cmc21 is significantly different from both the structure of (III) at 293 K and that found below 215 K, with weighted r.m.s. deviations of the Th, Tc and P atoms of 0.40 and 0.37 Å, respectively. An extensive network of weak intra- and intermolecular C—H⋯O hydrogen bonds found between the atoms of the nBu and [M′O4] groups probably influences the packing and the overall geometry of the molecules. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7681 Helliwell, M. Collison, D. John, G.H. May, I. Sarsfield, M.J. Sharrad, C.A. Sutton, A.D. 2006-02-01 doi:10.1107/S0108768105036931 International Union of Crystallography Crystals of the three actinide complexes [M(M′O4)4(TBPO)4], where MM′ = URe, ThRe, ThTc, respectively, studied between 293 and 100 K, show a number of reversible crystal-to-crystal phase transitions. The increase of order and differences in conformations of the complexes seen at the lower temperatures arise from a combination of the freezing of the nBu groups, the differing packing constraints of the various space groups and the network of weak C—H⋯O intra- and intermolecular hydrogen bonds. en PHASE TRANSITIONS; TWINNING; MEROHEDRY; HYDROGEN BONDS The crystal structures of the title complexes were measured at several temperatures between room temperature and 100 K. Each sample shows reversible crystal-to-crystal phase transitions as the temperature is varied. The behaviour of [U(ReO4)4(TBPO)4] (I) and [Th(ReO4)4(TBPO)4] (II) (TBPO = tri-n-butylphosphine oxide) is very similar; at room temperature, crystals of (I) and (II) are isostructural, with space group I\bar 42m, and reducing the temperature to 100 K causes a lowering of the space-group symmetry to C-centred cells, space groups Cc for (I) and Cmc21 for (II). The variation of lattice symmetry of [Th(TcO4)4(TBPO)4] (III) was found to be somewhat different, with the body-centred cubic space group, I\bar 43m, occurring at 293 K, a reduction of symmetry at 230 K to the C-centred orthorhombic space group, Cmc21, and a further transition to the primitive orthorhombic space group, Pbc21, below 215 K. Elucidation of the correct space-group symmetry and the subsequent refinement was complicated in some cases by the twinning by pseudo-merohedry that arises from the lowering of the space-group symmetry, occurring as the temperature is reduced. All three of the crystal structures determined at room temperature have high atomic displacement parameters, particularly of the nBu groups, and (III) shows disorder of some of the O atoms. The structures in the space group Cmc21, show some disorder of nBu groups, but are otherwise reasonably well ordered; the structures of (I) in Cc and (III) in Pbc21 are ordered, even to the ends of the alkyl chains. Inter-comparison of the structures measured below 293 K, using the program OFIT from the SHELXTL package, showed that generally, they are remarkably alike, with weighted r.m.s. deviations of the M, M′ and P atoms of less than 0.1 Å, as are the 293 K structures of (I) and (II) with their low-temperature counterparts. However, the structure of (III) measured in the space group Cmc21 is significantly different from both the structure of (III) at 293 K and that found below 215 K, with weighted r.m.s. deviations of the Th, Tc and P atoms of 0.40 and 0.37 Å, respectively. An extensive network of weak intra- and intermolecular C—H⋯O hydrogen bonds found between the atoms of the nBu and [M′O4] groups probably influences the packing and the overall geometry of the molecules. text/html Temperature-resolved study of three [M(M′O4)4(TBPO)4] complexes (MM′ = URe, ThRe, ThTc) text 62 1 Copyright (c) 2006 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2006-02-01 68 research papers 0108-7681 med@iucr.org 85 1600-5740 http://scripts.iucr.org/cgi-bin/paper?de5022 Detailed structures of nonasodium tetrakis(sulfate) chloride diperhydrate, Na9[SO4]4Cl·2H2O2, and its novel bromide analogue are compared. Hydrogen peroxide could not be resolved in a previously reported Na9[SO4]4Cl·2H2O2 substructure [tetragonal, P4/mnc; Adams et al. (1978), J. Chem. Soc. Chem. Commun. p. 288; Adams & Pritchard (1978), Acta Cryst. B34, 1428–1432]. However, on lowering the symmetry to P4/n, and using reflection data based on full unit-cells, the H2O2 solvate can be clearly seen. Although H2O2 molecules are not directly bonded to the halide anions, they exert considerable influence on the eight sodium cations that constitute each halide's coordination shell so that H2O2 ordering can be linked to halide dimensions. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7681 Pritchard, R.G. Begum, Z. Lau, Y.F. Austin, J. 2005-12-01 doi:10.1107/S010876810503212X International Union of Crystallography Both Na9[SO4]4Cl·2H2O2 and its newly discovered bromide analogue are extremely stable and can be used as sources of anhydrous H2O2 or, in the presence of H+, dihalogen. Despite being composed of small, inorganic molecules and ions, long H2O2 orientation sequences require the chloride unit-cell dimensions to be exceptionally large. The extended patterns of H2O2 orientations can be linked to displacements of the eight sodium cations that coordinate each halide anion. en SODIUM BROMIDE; ORIENTATION SEQUENCES; PERHYDRATE; SODIUM SULFATE; HYDROGEN PEROXIDE Detailed structures of nonasodium tetrakis(sulfate) chloride diperhydrate, Na9[SO4]4Cl·2H2O2, and its novel bromide analogue are compared. Hydrogen peroxide could not be resolved in a previously reported Na9[SO4]4Cl·2H2O2 substructure [tetragonal, P4/mnc; Adams et al. (1978), J. Chem. Soc. Chem. Commun. p. 288; Adams & Pritchard (1978), Acta Cryst. B34, 1428–1432]. However, on lowering the symmetry to P4/n, and using reflection data based on full unit-cells, the H2O2 solvate can be clearly seen. Although H2O2 molecules are not directly bonded to the halide anions, they exert considerable influence on the eight sodium cations that constitute each halide's coordination shell so that H2O2 ordering can be linked to halide dimensions. text/html Structures of Na9[SO4]4X·2H2O2, where X = Cl or Br, in which the halide anions orchestrate extended orientation sequences of H2O2 solvate molecules text 61 6 Copyright (c) 2005 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2005-12-01 663 research papers 0108-7681 med@iucr.org 668 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bs5020 Pyridine-3,5-dicarboxylic acid has been studied by single-crystal neutron diffraction at 15 and 296 K. Pyridine-3,5-dicarboxylic acid, in which the carboxylic acid protons have been replaced by deuterons, has also been studied at 15, 150 and 296 K. The protonated structure contains a short N⋯H⋯O hydrogen bond [N⋯O 2.523 (2) Å at 15 K]. Temperature-dependent proton migration occurs where the N—H distance in the hydrogen bond changes from 1.213 (4) Å at 15 K to 1.308 (6) Å at 300 K. In the deuterated structure the overall hydrogen-bond length increased [N⋯O 2.538 (3) Å at 15 K] and the magnitude of the migration increased so that the N—D distance changes from 1.151 (3) Å at 15 K to 1.457 (4) Å at 300 K. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7681 Cowan, J.A. Howard, J.A.K. McIntyre, G.J. Lo, S.M.-F. Williams, I.D. 2005-12-01 doi:10.1107/S0108768105030077 International Union of Crystallography Temperature-dependent proton migration has been observed in pyridine-3,5-dicarboxylic acid and also in pyridine-3,5-dicarboxylic acid in which the carboxylic acid protons have been replaced by deuterons. en VARIABLE-TEMPERATURE NEUTRON DIFFRACTION; HYDROGEN BONDING; DEUTERATED STRUCTURE; PROTON MIGRATION Pyridine-3,5-dicarboxylic acid has been studied by single-crystal neutron diffraction at 15 and 296 K. Pyridine-3,5-dicarboxylic acid, in which the carboxylic acid protons have been replaced by deuterons, has also been studied at 15, 150 and 296 K. The protonated structure contains a short N⋯H⋯O hydrogen bond [N⋯O 2.523 (2) Å at 15 K]. Temperature-dependent proton migration occurs where the N—H distance in the hydrogen bond changes from 1.213 (4) Å at 15 K to 1.308 (6) Å at 300 K. In the deuterated structure the overall hydrogen-bond length increased [N⋯O 2.538 (3) Å at 15 K] and the magnitude of the migration increased so that the N—D distance changes from 1.151 (3) Å at 15 K to 1.457 (4) Å at 300 K. text/html Variable-temperature neutron diffraction studies of the short, strong hydrogen bonds in the crystal structure of pyridine-3,5-dicarboxylic acid text 61 6 Copyright (c) 2005 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2005-12-01 724 research papers 0108-7681 med@iucr.org 730 1600-5740 http://scripts.iucr.org/cgi-bin/paper?ws5029 The crystal structure of cyclopropylamine at 1.2 GPa has been determined by X-ray diffraction methods. The structure of this phase is orthorhombic, space group Pbca and the unit-cell dimensions are a =  5.0741 (10), b  =  9.7594 (10) and c  =  13.305 (2) Å. Only one of the two H atoms of the amino group actively participates in the formation of the hydrogen-bonded chains, C(2) in graph-set notation, which lie parallel to the crystallographic a axis. Additionally, the topology of the crystal packing is studied using both Voronoi–Dirichlet polyhedra and Hirshfeld surface analyses for the low-temperature and the high-pressure structures of cyclopropyl­amine and the results are compared. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7681 Lozano-Casal, P. Allan, D.R. Parsons, S. 2005-12-01 doi:10.1107/S0108768105026327 International Union of Crystallography The crystal structure of cyclopropylamine has been determined at 1.2 GPa using high-pressure single-crystal X-ray diffraction techniques. The structure of this previously unobserved phase is orthorhombic. en CYCLOPROPYLAMINE; PRESSURE-INDUCED POLYMORPHISM The crystal structure of cyclopropylamine at 1.2 GPa has been determined by X-ray diffraction methods. The structure of this phase is orthorhombic, space group Pbca and the unit-cell dimensions are a =  5.0741 (10), b  =  9.7594 (10) and c  =  13.305 (2) Å. Only one of the two H atoms of the amino group actively participates in the formation of the hydrogen-bonded chains, C(2) in graph-set notation, which lie parallel to the crystallographic a axis. Additionally, the topology of the crystal packing is studied using both Voronoi–Dirichlet polyhedra and Hirshfeld surface analyses for the low-temperature and the high-pressure structures of cyclopropyl­amine and the results are compared. text/html Pressure-induced polymorphism in cyclopropyl­amine text 61 6 Copyright (c) 2005 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2005-12-01 717 research papers 0108-7681 med@iucr.org 723 1600-5740 http://scripts.iucr.org/cgi-bin/paper?av5037 The crystal structure of glipizide, used as a major treatment of type-2 diabetes, has been determined ab initio using variable-temperature laboratory X-ray powder diffraction combined with a direct-space Monte Carlo/simulated annealing methodology. The strengths of the intermolecular interactions (van der Waals, π–π stacking, hydrogen bonding and steric interlock) were quantitatively estimated using the thermal expansion data, which were collected in the same set of experiments as those used to determine the structure. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7681 Burley, J.C. 2005-12-01 doi:10.1107/S0108768105025991 International Union of Crystallography The crystal structure of the major diabetes treatment glipizide (glucotrol) has been determined. Intermolecular forces have been quantitatively evaluated from analysis of the thermal expansion of the lattice. en GLIPIZIDE; X-RAY POWDER DIFFRACTION; THERMAL EXPANSION The crystal structure of glipizide, used as a major treatment of type-2 diabetes, has been determined ab initio using variable-temperature laboratory X-ray powder diffraction combined with a direct-space Monte Carlo/simulated annealing methodology. The strengths of the intermolecular interactions (van der Waals, π–π stacking, hydrogen bonding and steric interlock) were quantitatively estimated using the thermal expansion data, which were collected in the same set of experiments as those used to determine the structure. text/html Structure and intermolecular interactions of glipizide from laboratory X-ray powder diffraction text 61 6 Copyright (c) 2005 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2005-12-01 710 research papers 0108-7681 med@iucr.org 716 1600-5740 http://scripts.iucr.org/cgi-bin/paper?de5016 An ongoing analysis of the supramolecular self-assembly of disubstituted cycloalkanes has led to the discovery of seven packing patterns built up from hydrogen-bonded homo- and heterochiral chains of racemic molecules, associated in either antiparallel or parallel arrays [Kálmán et al. (2001). Acta Cryst. B57, 539–550]. Two further patterns have been revealed in the close packing of analogous alicyclic β-amino acids [Fábián et al. (2005). Cryst. Growth Des. 5, 773–782]. Since each pattern is represented by at least one crystal structure, the chemical similarity and crystallographic forms of these crystals have facilitated the recognition that these patterns differ by one or two rotation(s) of the common motifs (e.g. dimers, tetramers, helices etc.), or the whole pattern may rotate through 180° in an oblique unit cell. Such non-crystallographic – with the exception of polymorphism – virtual rotations as a whole may be denoted by the expression morphotropism. According to Kitaigorodskii [(1961), Organic Chemical Crystallography, pp. 222–231. New York: Consultants Bureau], morphotropism is an attempt to keep the packing coefficient above 0.6 whenever there are alternative possibilities for the structures of closely related molecules. It has been found that crystals of stereoisomers are also frequently related by such virtual rotations. Similarly, non-crystallographic rotations effect bridges between homostructural crystals [Kálmán et al. (1993b). Acta Cryst. B49, 1039–1049] and occasionally hallmark the polymorphism of organic compounds [Kálmán et al. (2003) J. Am. Chem. Soc. 125, 34–35]. In polymorphs, however, such rotations really transform one molecule into another in order to achieve a better packing mediated by solvents, temperature etc. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7681 Kálmán, A. 2005-10-01 doi:10.1107/S0108768105023189 International Union of Crystallography Morphotropism (i.e. the non-crystallographic rotation of motifs) bridges the phenomena of isostructurality, polymorphism and (stereo)isomerism. Various forms of virtual and effective rotation of the common motifs, through either 90 or 180°, between chemically related structures, are presented. en MORPHOTROPISM; ISOSTRUCTURALITY; POLYMORPHISM An ongoing analysis of the supramolecular self-assembly of disubstituted cycloalkanes has led to the discovery of seven packing patterns built up from hydrogen-bonded homo- and heterochiral chains of racemic molecules, associated in either antiparallel or parallel arrays [Kálmán et al. (2001). Acta Cryst. B57, 539–550]. Two further patterns have been revealed in the close packing of analogous alicyclic β-amino acids [Fábián et al. (2005). Cryst. Growth Des. 5, 773–782]. Since each pattern is represented by at least one crystal structure, the chemical similarity and crystallographic forms of these crystals have facilitated the recognition that these patterns differ by one or two rotation(s) of the common motifs (e.g. dimers, tetramers, helices etc.), or the whole pattern may rotate through 180° in an oblique unit cell. Such non-crystallographic – with the exception of polymorphism – virtual rotations as a whole may be denoted by the expression morphotropism. According to Kitaigorodskii [(1961), Organic Chemical Crystallography, pp. 222–231. New York: Consultants Bureau], morphotropism is an attempt to keep the packing coefficient above 0.6 whenever there are alternative possibilities for the structures of closely related molecules. It has been found that crystals of stereoisomers are also frequently related by such virtual rotations. Similarly, non-crystallographic rotations effect bridges between homostructural crystals [Kálmán et al. (1993b). Acta Cryst. B49, 1039–1049] and occasionally hallmark the polymorphism of organic compounds [Kálmán et al. (2003) J. Am. Chem. Soc. 125, 34–35]. In polymorphs, however, such rotations really transform one molecule into another in order to achieve a better packing mediated by solvents, temperature etc. text/html Morphotropism: link between the isostructurality, polymorphism and (stereo)isomerism of organic crystals text 61 5 Copyright (c) 2005 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2005-10-01 536 research papers 0108-7681 med@iucr.org 547 1600-5740 http://scripts.iucr.org/cgi-bin/paper?ws5024 The low-temperature and high-pressure crystal structures of cyclobutanol (C4H7OH) have been determined using single-crystal X-ray diffraction techniques. At temperatures below 220 K, cyclobutanol crystallizes in the Aba2 space group (Z′ =  2) and its crystal structure is composed of pseudo-threefold hydrogen-bonded molecular catemers [assigned as C_2^2(4) in graph-set notation], which lie parallel to the crystallographic a axis. At a pressure of 1.3 GPa, the crystal symmetry changes to Pna21 (Z′  =  1) and the molecular catemers [expressed as C(2) in graph-set notation] adopt a pseudo-twofold arrangement. This structural behaviour is in agreement with our previous observations for phenol and its halogenated derivatives 2-chlorophenol and 4-fluorophenol, where pressure was found to favour a molecular packing more closely associated with small alkyl groups rather than that of relatively bulky alkyl groups. In addition, an examination of the molecular coordination environment in the low-temperature and high-pressure structures of cyclobutanol reveals that the change in structure on application of pressure appears to be driven by the molecules assuming a packing arrangement which more closely resembles that adopted in hard-sphere structures. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7681 McGregor, P.A. Allan, D.R. Parsons, S. Pulham, C.R. 2005-08-01 doi:10.1107/S0108768105019191 International Union of Crystallography The low-temperature and high-pressure crystal structures of cyclobutanol have been determined using single-crystal X-ray diffraction techniques. At temperatures below 493 K, cyclobutanol crystallizes in the Aba2 space group (Z′ = 2) and its crystal structure is composed of pseudo-threefold hydrogen-bonded molecular catemers. At a pressure of 1.3 GPa, the crystal symmetry changes to Pna21 (Z′ =1) and the molecular catemers adopt a pseudo-twofold arrangement. en LOW-TEMPERATURE AND HIGH-PRESSURE STRUCTURE; X-RAY DIFFRACTION; GRAPH-SET NOTATION; MOLECULAR PACKING The low-temperature and high-pressure crystal structures of cyclobutanol (C4H7OH) have been determined using single-crystal X-ray diffraction techniques. At temperatures below 220 K, cyclobutanol crystallizes in the Aba2 space group (Z′ =  2) and its crystal structure is composed of pseudo-threefold hydrogen-bonded molecular catemers [assigned as C_2^2(4) in graph-set notation], which lie parallel to the crystallographic a axis. At a pressure of 1.3 GPa, the crystal symmetry changes to Pna21 (Z′  =  1) and the molecular catemers [expressed as C(2) in graph-set notation] adopt a pseudo-twofold arrangement. This structural behaviour is in agreement with our previous observations for phenol and its halogenated derivatives 2-chlorophenol and 4-fluorophenol, where pressure was found to favour a molecular packing more closely associated with small alkyl groups rather than that of relatively bulky alkyl groups. In addition, an examination of the molecular coordination environment in the low-temperature and high-pressure structures of cyclobutanol reveals that the change in structure on application of pressure appears to be driven by the molecules assuming a packing arrangement which more closely resembles that adopted in hard-sphere structures. text/html The low-temperature and high-pressure crystal structures of cyclobutanol (C4H7OH) text 61 4 Copyright (c) 2005 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2005-08-01 449 research papers 0108-7681 med@iucr.org 454 1600-5740 http://scripts.iucr.org/cgi-bin/paper?de5017 A new approach to the crystal structure prediction of flexible molecules is presented. It is applied to piracetam, whose conformational polymorphs exhibit a variety of hydrogen-bond motifs but lack the intramolecular hydrogen bond found in the gas-phase ab initio optimized conformer. Stable crystal packing can result when favourable intermolecular interactions are made possible when the molecule distorts from the gas-phase conformation. If the resulting intermolecular lattice energy is sufficiently favourable to compensate for the intramolecular energy penalty associated with the suboptimal gas-phase conformation, then the crystal structure may be experimentally feasible. The new approach involves searching for low-energy crystal structures using a large number of rigid conformers, firstly to systematically explore which regions of conformational space could give rise to low-energy hydrogen-bonded crystal structures, and then to refine the search using crystallographic insight to optimize particular intermolecular interactions. The timely discovery of a new polymorph (form IV) by an independent experimental team allowed this approach to be validated by way of a `blind test' of crystal structure prediction. Form IV was successfully identified as the most favourable computed crystal structure with a conformation very distinct from that in the previously known polymorphs. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7681 Nowell, H. Price, S.L. 2005-10-01 doi:10.1107/S0108768105018549 International Union of Crystallography A new approach to the crystal structure prediction of flexible molecules is described and illustrated using a `blind' prediction of a recently solved conformational polymorph of piracetam. en CRYSTAL STRUCTURE PREDICTION OF FLEXIBLE MOLECULES; CONFORMATIONAL POLYMORPHISM; PIRACETAM A new approach to the crystal structure prediction of flexible molecules is presented. It is applied to piracetam, whose conformational polymorphs exhibit a variety of hydrogen-bond motifs but lack the intramolecular hydrogen bond found in the gas-phase ab initio optimized conformer. Stable crystal packing can result when favourable intermolecular interactions are made possible when the molecule distorts from the gas-phase conformation. If the resulting intermolecular lattice energy is sufficiently favourable to compensate for the intramolecular energy penalty associated with the suboptimal gas-phase conformation, then the crystal structure may be experimentally feasible. The new approach involves searching for low-energy crystal structures using a large number of rigid conformers, firstly to systematically explore which regions of conformational space could give rise to low-energy hydrogen-bonded crystal structures, and then to refine the search using crystallographic insight to optimize particular intermolecular interactions. The timely discovery of a new polymorph (form IV) by an independent experimental team allowed this approach to be validated by way of a `blind test' of crystal structure prediction. Form IV was successfully identified as the most favourable computed crystal structure with a conformation very distinct from that in the previously known polymorphs. text/html Validation of a search technique for crystal structure prediction of flexible molecules by application to piracetam text 61 5 Copyright (c) 2005 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2005-10-01 558 research papers 0108-7681 med@iucr.org 568 1600-5740 http://scripts.iucr.org/cgi-bin/paper?ws5026 The crystal structure of barbituric acid dihydrate (C4H4N2O3·2H2O) has twice been reported as orthorhombic, space group Pnma, with all atoms (except for CH2 H atoms) lying on the mirror plane [Al-Karaghouli et al. (1977). Acta Cryst. B33, 1655–1660; Jeffrey et al. (1961). Acta Cryst. 14, 881–887]. The present study has found that at low temperatures, below 200 K, the crystal structure is no longer orthorhombic but is non-merohedrally twinned monoclinic, space group P21/n. This phase is stable down to 100 K. Above 220 K the crystal structure is orthorhombic, and between 200 and 220 K the structure undergoes a phase change, with the monoclinic-to-orthorhombic phase transition itself taking place at around 216–217 K. The size of the β angle in the monoclinic structure is temperature dependent; at 100 K β is around 94° and it decreases in magnitude towards 90° as the temperature increases. Although the hydrogen-bonding motifs are the same for both crystal systems, there are significant differences in the crystal packing, in particular the out-of-plane displacement of the two water molecules and the sp3-hybridized C atom of barbituric acid. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7681 Nichol, G.S. Clegg, W. 2005-08-01 doi:10.1107/S0108768105017258 International Union of Crystallography Barbituric acid dihydrate undergoes a reversible orthorhombic-to-monoclinic phase transition when cooled below 200 K. This second phase is stable down to 100 K. There are clear differences in the crystal packing of the two phases, although the hydrogen-bonding motifs do not change. en PHASE TRANSITIONS; BARBITURIC ACID; LOW-TEMPERATURE CRYSTALLOGRAPHY The crystal structure of barbituric acid dihydrate (C4H4N2O3·2H2O) has twice been reported as orthorhombic, space group Pnma, with all atoms (except for CH2 H atoms) lying on the mirror plane [Al-Karaghouli et al. (1977). Acta Cryst. B33, 1655–1660; Jeffrey et al. (1961). Acta Cryst. 14, 881–887]. The present study has found that at low temperatures, below 200 K, the crystal structure is no longer orthorhombic but is non-merohedrally twinned monoclinic, space group P21/n. This phase is stable down to 100 K. Above 220 K the crystal structure is orthorhombic, and between 200 and 220 K the structure undergoes a phase change, with the monoclinic-to-orthorhombic phase transition itself taking place at around 216–217 K. The size of the β angle in the monoclinic structure is temperature dependent; at 100 K β is around 94° and it decreases in magnitude towards 90° as the temperature increases. Although the hydrogen-bonding motifs are the same for both crystal systems, there are significant differences in the crystal packing, in particular the out-of-plane displacement of the two water molecules and the sp3-hybridized C atom of barbituric acid. text/html A variable-temperature study of a phase transition in barbituric acid dihydrate text 61 4 Copyright (c) 2005 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2005-08-01 464 research papers 0108-7681 med@iucr.org 472 1600-5740 http://scripts.iucr.org/cgi-bin/paper?de5014 Following the interest generated by two previous blind tests of crystal structure prediction (CSP1999 and CSP2001), a third such collaborative project (CSP2004) was hosted by the Cambridge Crystallographic Data Centre. A range of methodologies used in searching for and ranking the likelihood of predicted crystal structures is represented amongst the 18 participating research groups, although most are based on the global minimization of the lattice energy. Initially the participants were given molecular diagrams of three molecules and asked to submit three predictions for the most likely crystal structure of each. Unlike earlier blind tests, no restriction was placed on the possible space group of the target crystal structures. Furthermore, Z′ = 2 structures were allowed. Part-way through the test, a partial structure report was discovered for one of the molecules, which could no longer be considered a blind test. Hence, a second molecule from the same category (small, rigid with common atom types) was offered to the participants as a replacement. Success rates within the three submitted predictions were lower than in the previous tests – there was only one successful prediction for any of the three `blind' molecules. For the `simplest' rigid molecule, this lack of success is partly due to the observed structure crystallizing with two molecules in the asymmetric unit. As in the 2001 blind test, there was no success in predicting the structure of the flexible molecule. The results highlight the necessity for better energy models, capable of simultaneously describing conformational and packing energies with high accuracy. There is also a need for improvements in search procedures for crystals with more than one independent molecule, as well as for molecules with conformational flexibility. These are necessary requirements for the prediction of possible thermodynamically favoured polymorphs. Which of these are actually realised is also influenced by as yet insufficiently understood processes of nucleation and crystal growth. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7681 Day, G.M. Motherwell, W.D.S. Ammon, H.L. Boerrigter, S.X.M. Della Valle, R.G. Venuti, E. Dzyabchenko, A. Dunitz, J.D. Schweizer, B. van Eijck, B.P. Erk, P. Facelli, J.C. Bazterra, V.E. Ferraro, M.B. Hofmann, D.W.M. Leusen, F.J.J. Liang, C. Pantelides, C.C. Karamertzanis, P.G. Price, S.L. Lewis, T.C. Nowell, H. Torrisi, A. Scheraga, H.A. Arnautova, Y.A. Schmidt, M.U. Verwer, P. 2005-10-01 doi:10.1107/S0108768105016563 International Union of Crystallography The findings of the third blind test of crystal structure prediction are presented and discussed in the context of the previous collaborations – CSP1999 and CSP2001. en PREDICTION; BLIND; POLYMORPHS; CRYSTAL STRUCTURE PREDICTION Following the interest generated by two previous blind tests of crystal structure prediction (CSP1999 and CSP2001), a third such collaborative project (CSP2004) was hosted by the Cambridge Crystallographic Data Centre. A range of methodologies used in searching for and ranking the likelihood of predicted crystal structures is represented amongst the 18 participating research groups, although most are based on the global minimization of the lattice energy. Initially the participants were given molecular diagrams of three molecules and asked to submit three predictions for the most likely crystal structure of each. Unlike earlier blind tests, no restriction was placed on the possible space group of the target crystal structures. Furthermore, Z′ = 2 structures were allowed. Part-way through the test, a partial structure report was discovered for one of the molecules, which could no longer be considered a blind test. Hence, a second molecule from the same category (small, rigid with common atom types) was offered to the participants as a replacement. Success rates within the three submitted predictions were lower than in the previous tests – there was only one successful prediction for any of the three `blind' molecules. For the `simplest' rigid molecule, this lack of success is partly due to the observed structure crystallizing with two molecules in the asymmetric unit. As in the 2001 blind test, there was no success in predicting the structure of the flexible molecule. The results highlight the necessity for better energy models, capable of simultaneously describing conformational and packing energies with high accuracy. There is also a need for improvements in search procedures for crystals with more than one independent molecule, as well as for molecules with conformational flexibility. These are necessary requirements for the prediction of possible thermodynamically favoured polymorphs. Which of these are actually realised is also influenced by as yet insufficiently understood processes of nucleation and crystal growth. text/html A third blind test of crystal structure prediction text 61 5 Copyright (c) 2005 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2005-10-01 511 research papers 0108-7681 med@iucr.org 527 1600-5740 http://scripts.iucr.org/cgi-bin/paper?dr5005 Simulations of electron diffraction patterns for each of the known perovskite tilt systems have been performed. The conditions for the appearance of superlattice reflections arising from rotations of the octahedra are modified to take into account the effects of different tilt systems for kinematical diffraction. The use of selected-area electron diffraction as a tool for perovskite structure determination is reviewed and examples are included. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7681 Woodward, D.I. Reaney, I.M. 2005-08-01 doi:10.1107/S0108768105015521 International Union of Crystallography Simulations of electron diffraction patterns have been performed for each of the known perovskite tilt systems. Full details of the allowed reflections for each system are presented along with examples showing how simple selected-area diffraction patterns can be used to identify tilt systems. en ELECTRON DIFFRACTION; TILTED PEROVSKITES; SUPERLATTICE REFLECTIONS Simulations of electron diffraction patterns for each of the known perovskite tilt systems have been performed. The conditions for the appearance of superlattice reflections arising from rotations of the octahedra are modified to take into account the effects of different tilt systems for kinematical diffraction. The use of selected-area electron diffraction as a tool for perovskite structure determination is reviewed and examples are included. text/html Electron diffraction of tilted perovskites text 61 4 Copyright (c) 2005 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2005-08-01 387 research papers 0108-7681 med@iucr.org 399 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bk5018 Hypothetical binodal zeolitic structures (structures containing two kinds of tetrahedral sites) were systematically enumerated using tiling theory and characterized by computational chemistry methods. Each of the 109 refineable topologies based on `simple tilings' was converted into a silica polymorph and its energy minimized using the GULP program with the Sanders–Catlow silica potential. Optimized structural parameters, framework energies relative to α-quartz and volumes accessible to sorption have been calculated. Eleven of the 30 known binodal topologies listed in the Atlas of Zeolite Framework Types were found, leaving 98 topologies that were unknown previously. The chemical feasibility of each structure as a zeolite was evaluated by means of a feasibility factor derived from the correlation between lattice energy and framework density. Structures are divided into 15 families, based on common structural features. Many `feasible' structures contain only small pores. Several very open structures were also enumerated, although they contain three-membered rings which are thermodynamically dis­favoured and not found in conventional zeolites. We believe that such topologies may be realizable as framework materials, but with different elemental compositions to those normally associated with zeolites. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7681 Simperler, A. Foster, M.D. Delgado Friedrichs, O. Bell, R.G. Almeida Paz, F.A. Klinowski, J. 2005-06-01 doi:10.1107/S0108768105013340 International Union of Crystallography Hypothetical zeolitic structures containing two kinds of tetrahedral site are systematically enumerated using tiling theory and evaluated as silica polymorphs by computational chemistry methods. The structures, most of them new, are divided into 15 families, based on common topological features, and the chemical feasibility of each is estimated in terms of the correlation between lattice energy and framework density. en TILING THEORY; ENUMERATION; ZEOLITES; HYPOTHETICAL STRUCTURES Hypothetical binodal zeolitic structures (structures containing two kinds of tetrahedral sites) were systematically enumerated using tiling theory and characterized by computational chemistry methods. Each of the 109 refineable topologies based on `simple tilings' was converted into a silica polymorph and its energy minimized using the GULP program with the Sanders–Catlow silica potential. Optimized structural parameters, framework energies relative to α-quartz and volumes accessible to sorption have been calculated. Eleven of the 30 known binodal topologies listed in the Atlas of Zeolite Framework Types were found, leaving 98 topologies that were unknown previously. The chemical feasibility of each structure as a zeolite was evaluated by means of a feasibility factor derived from the correlation between lattice energy and framework density. Structures are divided into 15 families, based on common structural features. Many `feasible' structures contain only small pores. Several very open structures were also enumerated, although they contain three-membered rings which are thermodynamically dis­favoured and not found in conventional zeolites. We believe that such topologies may be realizable as framework materials, but with different elemental compositions to those normally associated with zeolites. text/html Hypothetical binodal zeolitic frameworks text 61 3 Copyright (c) 2005 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2005-06-01 263 research papers 0108-7681 med@iucr.org 279 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bk0148 A new survey of the Cambridge Structural Database has uncovered 115 additional crystal structures that were described in the space group P1, but would be better described in groups of higher symmetries. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7681 Marsh, R.E. 2005-06-01 doi:10.1107/S0108768105009651 International Union of Crystallography A new survey of the Cambridge Structural Database has uncovered 115 additional crystal structures that were described in the space group P1, but would be better described in groups of higher symmetries. en SPACE GROUP REASSIGNMENT; CAMBRIDGE STRUCTURAL DATABASE A new survey of the Cambridge Structural Database has uncovered 115 additional crystal structures that were described in the space group P1, but would be better described in groups of higher symmetries. text/html Space group P1: an update text 61 3 Copyright (c) 2005 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2005-06-01 359 letters to the editor 0108-7681 med@iucr.org 359 1600-5740 http://scripts.iucr.org/cgi-bin/paper?lc5021 The MnNb2O6–FeNb2O6 solid solution has been investigated by Fe–K- and Mn–K-edge X-ray absorption (XANES and EXAFS), and Mössbauer spectroscopy. The first-shell M—O bond lengths deduced from EXAFS show a fairly small compositional dependence. A degree of static disorder, which increases with increasing manganese content, is clearly seen by the loss of correlation for the next-neighbour (NN) interaction. Hyperfine parameters from Mössbauer spectra are consistent with variations in the average environment, as recorded by X-ray data. Line broadening of the Mössbauer spectra provides evidence for next-neighbour effects and is consistent with there being no significant clustering of Fe or Mn within the samples. There appear to be differences in the way the columbite structure accommodates Fe2+ and Mn2+ ions. In ferrocolumbite all the Fe octahedra are close to being identical, while there are local structural heterogeneities at a longer length scale, presumably in ordering the precise topology of polyhedra immediately adjacent to the octahedron. By contrast, the manganocolumbite seems to have some diversity in the precise coordination at the MnO6 octahedra, but a greater uniformity in how the adjacent polyhedra are configured around them. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7681 Tarantino, S.C. Ghigna, P. McCammon, C. Amantea, R. Carpenter, M.A. 2005-06-01 doi:10.1107/S0108768105008116 International Union of Crystallography The short-range structure of Mn1 − xFexNb2O6 columbites has been studied by Mössbauer and X-ray absorption spectroscopies. Length scales of observed local structural heterogeneities change across the solid solution. en X-RAY ABSORPTION SPECTROSCOPY; MOSSBAUER SPECTROSCOPY; SOLID SOLUTION; LOCAL STRUCTURE The MnNb2O6–FeNb2O6 solid solution has been investigated by Fe–K- and Mn–K-edge X-ray absorption (XANES and EXAFS), and Mössbauer spectroscopy. The first-shell M—O bond lengths deduced from EXAFS show a fairly small compositional dependence. A degree of static disorder, which increases with increasing manganese content, is clearly seen by the loss of correlation for the next-neighbour (NN) interaction. Hyperfine parameters from Mössbauer spectra are consistent with variations in the average environment, as recorded by X-ray data. Line broadening of the Mössbauer spectra provides evidence for next-neighbour effects and is consistent with there being no significant clustering of Fe or Mn within the samples. There appear to be differences in the way the columbite structure accommodates Fe2+ and Mn2+ ions. In ferrocolumbite all the Fe octahedra are close to being identical, while there are local structural heterogeneities at a longer length scale, presumably in ordering the precise topology of polyhedra immediately adjacent to the octahedron. By contrast, the manganocolumbite seems to have some diversity in the precise coordination at the MnO6 octahedra, but a greater uniformity in how the adjacent polyhedra are configured around them. text/html Local structural properties of (Mn,Fe)Nb2O6 from Mössbauer and X-ray absorption spectroscopy text 61 3 Copyright (c) 2005 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2005-06-01 250 research papers 0108-7681 med@iucr.org 257 1600-5740 http://scripts.iucr.org/cgi-bin/paper?sx5028 The homologous series of three-atom bridged biaryls comprising 5,7-dihydro-1,2,3,9,10,11-hexamethoxydibenzo[c,e]oxepine, 6,7-dihydro-1,2,3,9,10,11-hexamethoxy-6-methyl-5H-dibenzo[c,e]azepinium chloride, 5,7-dihydro-1,2,3,9,10,11-hexamethoxydibenzo[c,e]thiepine, and the 6-oxide and 6,6-dioxide derivatives of the latter have been characterized by X-ray crystal structure analysis. Within this series the endocyclic and exocyclic biaryl dihedral angles vary over 10° ranges, reflecting the changing balance of intramolecular (steric, geometric) and intermolecular (crystal packing) forces, the former being potential control elements for fine-tuning the helicity of the biaryl system. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7681 Edwards, D.J. Pritchard, R.G. Wallace, T.W. 2005-06-01 doi:10.1107/S0108768105006713 International Union of Crystallography The X-ray crystal structures of five polymethoxylated 1,1′-biphenyls, each with a 2,2′-bridge of the form CH2—X—CH2 (X = O, N or S), provide insight into the extent to which the design of the bridge influences the degree of helicity in such biaryls. The five compounds are analogues of the alkaloid colchicine, whose tubulin-binding properties are strongly dependent on this angle. en THREE-ATOM BRIDGED BIARYLS; HELICITY; TUBULIN-BINDING PROPERTIES The homologous series of three-atom bridged biaryls comprising 5,7-dihydro-1,2,3,9,10,11-hexamethoxydibenzo[c,e]oxepine, 6,7-dihydro-1,2,3,9,10,11-hexamethoxy-6-methyl-5H-dibenzo[c,e]azepinium chloride, 5,7-dihydro-1,2,3,9,10,11-hexamethoxydibenzo[c,e]thiepine, and the 6-oxide and 6,6-dioxide derivatives of the latter have been characterized by X-ray crystal structure analysis. Within this series the endocyclic and exocyclic biaryl dihedral angles vary over 10° ranges, reflecting the changing balance of intramolecular (steric, geometric) and intermolecular (crystal packing) forces, the former being potential control elements for fine-tuning the helicity of the biaryl system. text/html Fine-tuning of biaryl dihedral angles: structural characterization of five homologous three-atom bridged biphenyls by X-ray crystallography text 61 3 Copyright (c) 2005 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2005-06-01 335 research papers 0108-7681 med@iucr.org 345 1600-5740 http://scripts.iucr.org/cgi-bin/paper?ws5022 The title compound, C18H17NO4, crystallizes from ethanol at ambient temperature as two concomitant polymorphs (I) and (II), both monoclinic P21/c with Z′ = 1. The less abundant form (I) undergoes a reversible phase-transition at ca 173 K to a third monoclinic polymorph (III), P21/n, with Z′ = 2, while the more abundant polymorph (II) is unchanged down to 120 K. In each polymorph of (I)–(III) the molecules are linked by pairs of O—H⋯O hydrogen bonds into cyclic dimers which are crystallographically centrosymmetric in (I) and (II), and approximately, but not crystallographically, centrosymmetric in (III). There are no direction-specific interactions between the hydrogen-bonded dimers in polymorph (I); in polymorph (II) the dimers are linked into sheets by C—H⋯N and C—H⋯π(arene) hydrogen bonds; in polymorph (III) the dimers are linked into chains by a C—H⋯π(arene) hydrogen bond. The interconversion of polymorphs (I) and (III) is a simple displacive phase transition. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7681 Skakle, J.M.S. Low, J.N. Wardell, J.L. Glidewell, C. 2005-06-01 doi:10.1107/S0108768105007421 International Union of Crystallography Three polymorphic forms of (E)-[1-(4-methoxyphenyl)-3-phenyl-2-propenylideneamino]oxyacetic acid all contain hydrogen-bonded dimers, but the interactions between these dimers are all different. en POLYMORPHISM; PHASE CHANGE; HYDROGEN BONDING; CYCLIC DIMERS The title compound, C18H17NO4, crystallizes from ethanol at ambient temperature as two concomitant polymorphs (I) and (II), both monoclinic P21/c with Z′ = 1. The less abundant form (I) undergoes a reversible phase-transition at ca 173 K to a third monoclinic polymorph (III), P21/n, with Z′ = 2, while the more abundant polymorph (II) is unchanged down to 120 K. In each polymorph of (I)–(III) the molecules are linked by pairs of O—H⋯O hydrogen bonds into cyclic dimers which are crystallographically centrosymmetric in (I) and (II), and approximately, but not crystallographically, centrosymmetric in (III). There are no direction-specific interactions between the hydrogen-bonded dimers in polymorph (I); in polymorph (II) the dimers are linked into sheets by C—H⋯N and C—H⋯π(arene) hydrogen bonds; in polymorph (III) the dimers are linked into chains by a C—H⋯π(arene) hydrogen bond. The interconversion of polymorphs (I) and (III) is a simple displacive phase transition. text/html Concomitant polymorphism and a temperature-dependent phase change in (E)-[1-(4-methoxyphenyl)-3-phenyl-2-propenylideneamino]oxyacetic acid text 61 3 Copyright (c) 2005 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2005-06-01 321 research papers 0108-7681 med@iucr.org 328 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bm5022 The six isomeric N-(iodophenyl)nitrophthalimides, C14H7IN2O4, have been synthesized and the structures of five of them are reported. In N-(4-iodophenyl)-4-nitrophthalimide [(I), orthorhombic P212121] the molecules are linked into sheets by a combination of four independent C—H⋯O hydrogen bonds, but I⋯O interactions are absent. The isomers N-(3-iodophenyl)-4-nitrophthalimide [(II), monoclinic P21/c] and N-(2-iodophenyl)-4-nitrophthalimide [(III), monoclinic P21/n] both form sheets, but in (II) the molecules are linked by a combination of one two-centre iodo⋯nitro interaction and one C—H⋯O hydrogen bond into sheets containing R_4^4(30) rings, while in (III) they are linked by an iodo⋯carbonyl interaction and a C—H⋯O hydrogen bond into sheets or R_4^4(26) rings. Three-dimensional supramolecular structures are formed in both N-(4-iodophenyl)-3-nitrophthalimide [(IV), monoclinic P21/n] and N-(3-iodophenyl)-3-nitrophthalimide [(V), orthorhombic, P212121]. In (IV) the molecules are linked by a three-centre iodo⋯nitro interaction, three C—H⋯O hydrogen bonds and an aromatic π⋯π stacking interaction, but the framework in (V) is generated by a two-centre iodo⋯nitro interaction and only two C—H⋯O hydrogen bonds: aromatic π⋯π stacking interactions are absent from (V). Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7681 Glidewell, C. Low, J.N. Skakle, J.M.S. Wardell, S.M.S.V. Wardell, J.L. 2005-04-01 doi:10.1107/S0108768105004234 International Union of Crystallography Five isomeric N-(iodophenyl)-nitrophthalimides all exhibit a different range of intermolecular interactions, including C—H⋯O(nitro) and C—H⋯O(carbonyl) hydrogen bonds, two- and three-centre iodo⋯nitro and two-centre iodo⋯carbonyl interactions, and aromatic π⋯π stacking interactions; all five isomers have qualitatively different supramolecular structures. en HYDROGEN BONDS; STACKING INTERACTIONS; SUPRAMOLECULAR STRUCTURES The six isomeric N-(iodophenyl)nitrophthalimides, C14H7IN2O4, have been synthesized and the structures of five of them are reported. In N-(4-iodophenyl)-4-nitrophthalimide [(I), orthorhombic P212121] the molecules are linked into sheets by a combination of four independent C—H⋯O hydrogen bonds, but I⋯O interactions are absent. The isomers N-(3-iodophenyl)-4-nitrophthalimide [(II), monoclinic P21/c] and N-(2-iodophenyl)-4-nitrophthalimide [(III), monoclinic P21/n] both form sheets, but in (II) the molecules are linked by a combination of one two-centre iodo⋯nitro interaction and one C—H⋯O hydrogen bond into sheets containing R_4^4(30) rings, while in (III) they are linked by an iodo⋯carbonyl interaction and a C—H⋯O hydrogen bond into sheets or R_4^4(26) rings. Three-dimensional supramolecular structures are formed in both N-(4-iodophenyl)-3-nitrophthalimide [(IV), monoclinic P21/n] and N-(3-iodophenyl)-3-nitrophthalimide [(V), orthorhombic, P212121]. In (IV) the molecules are linked by a three-centre iodo⋯nitro interaction, three C—H⋯O hydrogen bonds and an aromatic π⋯π stacking interaction, but the framework in (V) is generated by a two-centre iodo⋯nitro interaction and only two C—H⋯O hydrogen bonds: aromatic π⋯π stacking interactions are absent from (V). text/html Isomeric N-(iodophenyl)nitrophthalimides: interplay of C—H⋯O hydrogen bonds, iodo⋯nitro and iodo⋯carbonyl interactions, and aromatic π⋯π stacking interactions text 61 2 Copyright (c) 2005 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2005-04-01 227 research papers 0108-7681 med@iucr.org 237 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bs5009 The structure of a high-loading complex of ZSM-5 with 6.4 toluene molecules per unit cell has been determined by single-crystal X-ray diffraction. At least three kinds of toluene molecules were identified in the unit cell. Two disordered toluene molecules were located at the intersection of the straight and sinusoidal channels, the third in the sinusoidal channel. One (TOL1) of the two toluene orientations at the intersection was similar to that of p-dichlorobenzene at the intersection in high-loaded H-ZSM-5/p-xylene (hereafter 8PARA) and high-loaded H-ZSM-5/p-dichlorobenzene (hereafter 8PDCB) complexes, respectively. The other toluene orientation (TOL2) at the intersection was similar to those of p-xylene or p-dichlorobenzene at the intersection in the low-loaded p-dichlorobenzene complex (hereafter 2.6PDCB). A third toluene orientation (TOL3) existed in the sinusoidal channel; its orientation was similar to those of p-xylene and p-dichlorobenzene in the sinusoidal channels in 8PARA and 8PDCB complexes, respectively. If the occupancy of TOL2 at the intersection increases with temperature, TOL2 will connect with TOL3 in the sinusoidal channel and form the intermediate diphenylmethane Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7681 Nishi, K. Hidaka, A. Yokomori, Y. 2005-04-01 doi:10.1107/S0108768105003186 International Union of Crystallography We have investigated the structure of toluene6.4-ZSM-5 by X-ray single-crystal diffraction and have shown the toluene disproportionation reaction on ZSM-5 zeolite. en TOLUENE; ZSM-5; DISPROPORTIONATION The structure of a high-loading complex of ZSM-5 with 6.4 toluene molecules per unit cell has been determined by single-crystal X-ray diffraction. At least three kinds of toluene molecules were identified in the unit cell. Two disordered toluene molecules were located at the intersection of the straight and sinusoidal channels, the third in the sinusoidal channel. One (TOL1) of the two toluene orientations at the intersection was similar to that of p-dichlorobenzene at the intersection in high-loaded H-ZSM-5/p-xylene (hereafter 8PARA) and high-loaded H-ZSM-5/p-dichlorobenzene (hereafter 8PDCB) complexes, respectively. The other toluene orientation (TOL2) at the intersection was similar to those of p-xylene or p-dichlorobenzene at the intersection in the low-loaded p-dichlorobenzene complex (hereafter 2.6PDCB). A third toluene orientation (TOL3) existed in the sinusoidal channel; its orientation was similar to those of p-xylene and p-dichlorobenzene in the sinusoidal channels in 8PARA and 8PDCB complexes, respectively. If the occupancy of TOL2 at the intersection increases with temperature, TOL2 will connect with TOL3 in the sinusoidal channel and form the intermediate diphenylmethane text/html Structure of toluene6.4-ZSM-5 and the toluene disproportionation reaction on ZSM-5 text 61 2 Copyright (c) 2005 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2005-04-01 160 research papers 0108-7681 med@iucr.org 163 1600-5740 http://scripts.iucr.org/cgi-bin/paper?ws5017 The crystal structure of l-serine has been determined at room temperature at pressures between 0.3 and 4.8 GPa. The structure of this phase (hereafter termed l-serine-I), which consists of the molecules in their zwitterionic tautomer, is orthorhombic, space group P212121. The least compressible cell dimension (c), corresponds to chains of head-to-tail NH⋯carboxylate hydrogen bonds. The most compressible direction is along b, and the pressure-induced distortion in this direction takes the form of closing up voids in the middle of R-type hydrogen-bonded ring motifs. This occurs by a change in the geometry of hydrogen-bonded chains connecting the hydroxyl groups of the —CH2OH side chains. These hydrogen bonds are the longest conventional hydrogen bonds in the system at ambient pressure, having an O⋯O separation of 2.918 (4) Å and an O⋯O⋯O angle of 148.5 (2)°; at 4.8 GPa these parameters are 2.781 (11) and 158.5 (7)°. Elsewhere in the structure one NH⋯O interaction reaches an N⋯O separation of 2.691 (13) Å at 4.8 GPa. This is amongst the shortest of this type of interaction to have been observed in an amino acid crystal structure. Above 4.8 GPa the structure undergoes a single-crystal-to-single-crystal phase transition to a hitherto uncharacterized polymorph, which we designate l-serine-II. The OH⋯OH hydrogen-bonded chains of l-serine-I are replaced in l-serine-II by shorter OH⋯carboxyl interactions, which have an O⋯O separation of 2.62 (2) Å. This phase transition occurs via a change from a gauche to an anti conformation of the OH group, and a change in the NCαCO torsion angle from −178.1 (2)° at 4.8 GPa to −156.3 (10)° at 5.4 GPa. Thus, the same topology appears in both crystal forms, which explains why it occurs from one single-crystal form to another. The transition to l-serine-II is also characterized by the closing-up of voids which occur in the centres of other R-type motifs elsewhere in the structure. There is a marked increase in CH⋯O hydrogen bonding in both phases relative to l-serine-I at ambient pressure. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7681 Moggach, S.A. Allan, D.R. Morrison, C.A. Parsons, S. Sawyer, L. 2005-02-01 doi:10.1107/S0108768104031787 International Union of Crystallography The crystal structure of l-serine has been determined at room temperature at pressures from 0.3 to 4.8 GPa. Above 4.8 GPa the structure transforms to a new polymorph, the structure of which has been determined at 5.4 GPa. en PRESSURE; POLYMORPHISM; HYDROGEN BONDING; TOPOLOGY The crystal structure of l-serine has been determined at room temperature at pressures between 0.3 and 4.8 GPa. The structure of this phase (hereafter termed l-serine-I), which consists of the molecules in their zwitterionic tautomer, is orthorhombic, space group P212121. The least compressible cell dimension (c), corresponds to chains of head-to-tail NH⋯carboxylate hydrogen bonds. The most compressible direction is along b, and the pressure-induced distortion in this direction takes the form of closing up voids in the middle of R-type hydrogen-bonded ring motifs. This occurs by a change in the geometry of hydrogen-bonded chains connecting the hydroxyl groups of the —CH2OH side chains. These hydrogen bonds are the longest conventional hydrogen bonds in the system at ambient pressure, having an O⋯O separation of 2.918 (4) Å and an O⋯O⋯O angle of 148.5 (2)°; at 4.8 GPa these parameters are 2.781 (11) and 158.5 (7)°. Elsewhere in the structure one NH⋯O interaction reaches an N⋯O separation of 2.691 (13) Å at 4.8 GPa. This is amongst the shortest of this type of interaction to have been observed in an amino acid crystal structure. Above 4.8 GPa the structure undergoes a single-crystal-to-single-crystal phase transition to a hitherto uncharacterized polymorph, which we designate l-serine-II. The OH⋯OH hydrogen-bonded chains of l-serine-I are replaced in l-serine-II by shorter OH⋯carboxyl interactions, which have an O⋯O separation of 2.62 (2) Å. This phase transition occurs via a change from a gauche to an anti conformation of the OH group, and a change in the NCαCO torsion angle from −178.1 (2)° at 4.8 GPa to −156.3 (10)° at 5.4 GPa. Thus, the same topology appears in both crystal forms, which explains why it occurs from one single-crystal form to another. The transition to l-serine-II is also characterized by the closing-up of voids which occur in the centres of other R-type motifs elsewhere in the structure. There is a marked increase in CH⋯O hydrogen bonding in both phases relative to l-serine-I at ambient pressure. text/html Effect of pressure on the crystal structure of l-serine-I and the crystal structure of l-serine-II at 5.4 GPa text 61 1 Copyright (c) 2005 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2005-02-01 58 research papers 0108-7681 med@iucr.org 68 1600-5740 http://scripts.iucr.org/cgi-bin/paper?av5021 A temperature-controlled X-ray powder diffraction experiment, complemented with TGA and DSC analysis, allowed us to follow changes in the molecular conformation and hydrogen-bond patterns of 4-piperidinecarboxylic acid. The presence of three phases is confirmed. Phase 1 represents the monohydrated form of 4-piperidinecarboxylic acid, which exists from room temperature to 359 K, where dehydration occurs. Phase 2 measured at 363 K corresponds to an anhydrous form of the acid. At ca 458 K the onset of a second, more gradual transition is observed, which ends at around 543 K. Phase 3 measured at 543 K is a high-temperature anhydrous form of the acid. The structures of phases 2 and 3 were solved from synchrotron powder diffraction data by simulated annealing using the DASH program and refined by the Rietveld method. The phase changes are accompanied by modification of the hydrogen-bond patterns and of the torsional orientation of the terminal carboxylate group. This group makes a 49° rotation about the C1—C2 bond during the first transition. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7681 Mora, A.J. Avila, E.E. Delgado, G.E. Fitch, A.N. Brunelli, M. 2005-02-01 doi:10.1107/S0108768104031738 International Union of Crystallography The molecular conformation and hydrogen-bond patterns of 4-piperidinecarboxylic acid at various temperatures were investigated by means of X-ray powder diffraction, TGA and DSC. en TEMPERATURE-CONTROLLED POWDER DIFFRACTION; HYDROGEN BONDS; RIETVELD REFINEMENT A temperature-controlled X-ray powder diffraction experiment, complemented with TGA and DSC analysis, allowed us to follow changes in the molecular conformation and hydrogen-bond patterns of 4-piperidinecarboxylic acid. The presence of three phases is confirmed. Phase 1 represents the monohydrated form of 4-piperidinecarboxylic acid, which exists from room temperature to 359 K, where dehydration occurs. Phase 2 measured at 363 K corresponds to an anhydrous form of the acid. At ca 458 K the onset of a second, more gradual transition is observed, which ends at around 543 K. Phase 3 measured at 543 K is a high-temperature anhydrous form of the acid. The structures of phases 2 and 3 were solved from synchrotron powder diffraction data by simulated annealing using the DASH program and refined by the Rietveld method. The phase changes are accompanied by modification of the hydrogen-bond patterns and of the torsional orientation of the terminal carboxylate group. This group makes a 49° rotation about the C1—C2 bond during the first transition. text/html Temperature effects on the hydrogen-bond patterns in 4-piperidinecarboxylic acid text 61 1 Copyright (c) 2005 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2005-02-01 96 research papers 0108-7681 med@iucr.org 102 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bs5012 2-Fluorophenol, 3-fluorophenol and 3-chlorophenol were recrystallized from frozen solids at 260, 263 and 283 K. All compounds were also crystallized by the application of high pressure (0.36, 0.12 and 0.10 GPa). While 3-fluorophenol and 3-chlorophenol yielded the same phases under both conditions, different polymorphs were obtained for 2-fluorophenol. 4-Chlorophenol was crystallized both from the melt and from benzene to yield two different ambient-pressure polymorphs; crystallization from the melt at 0.02 GPa yielded the same phase as from benzene at ambient pressure. 3-Fluorophenol is unusual in forming a hydrogen-bonded chain along a 21 screw axis. Such behaviour is usually only observed for small alcohols, but here it appears to be stabilized by intermolecular C—H⋯F hydrogen-bond formation. 3-Chlorophenol is a more typical large alcohol and emulates a fourfold screw axis with two independent molecules positioned about a 21 axis, although there are significant distortions from this ideal geometry. The two phases of 4-chlorophenol consist of chains or rings connected by C—Cl⋯H interactions. The low-temperature and high-pressure polymorphs of 2-fluorophenol consist of chains of molecules connected through OH⋯OH hydrogen bonds; while inter-chain C—H⋯F interactions are significant at high pressure, there are none in the low-temperature form. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7681 Oswald, I.D.H. Allan, D.R. Motherwell, W.D.S. Parsons, S. 2005-02-01 doi:10.1107/S0108768104030617 International Union of Crystallography The crystal structures of 2-fluorophenol, 3-fluorophenol, 3-chloro­phenol and 4-chlorophenol have been obtained at low-temperature and at high pressure. en PHENOLS; LOW TEMPERATURE; HIGH PRESSURE; HYDROGEN BONDING; POLYMORPHISM 2-Fluorophenol, 3-fluorophenol and 3-chlorophenol were recrystallized from frozen solids at 260, 263 and 283 K. All compounds were also crystallized by the application of high pressure (0.36, 0.12 and 0.10 GPa). While 3-fluorophenol and 3-chlorophenol yielded the same phases under both conditions, different polymorphs were obtained for 2-fluorophenol. 4-Chlorophenol was crystallized both from the melt and from benzene to yield two different ambient-pressure polymorphs; crystallization from the melt at 0.02 GPa yielded the same phase as from benzene at ambient pressure. 3-Fluorophenol is unusual in forming a hydrogen-bonded chain along a 21 screw axis. Such behaviour is usually only observed for small alcohols, but here it appears to be stabilized by intermolecular C—H⋯F hydrogen-bond formation. 3-Chlorophenol is a more typical large alcohol and emulates a fourfold screw axis with two independent molecules positioned about a 21 axis, although there are significant distortions from this ideal geometry. The two phases of 4-chlorophenol consist of chains or rings connected by C—Cl⋯H interactions. The low-temperature and high-pressure polymorphs of 2-fluorophenol consist of chains of molecules connected through OH⋯OH hydrogen bonds; while inter-chain C—H⋯F interactions are significant at high pressure, there are none in the low-temperature form. text/html Structures of the monofluoro- and monochloro­phenols at low temperature and high pressure text 61 1 Copyright (c) 2005 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2005-02-01 69 research papers 0108-7681 med@iucr.org 79 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bm5020 The structures of six 1-phenylethylammonium tartrates have been determined and in each of them a distinctive hydrogen-bonded anion substructure can be identified. (S)-1-Phenyl­ethylammonium (R,R)-hydrogen tartrate [(I), P21, Z′ = 1] contains anion sheets built from a single type of R_4^4(22) ring with cations pendent, via three N—H⋯O hydrogen bonds, from just one face of the sheet. (S)-1-Phenylethylammonium rac-hydrogen tartrate [(II), P21, Z′ = 2] and its enantiomorph (R)-1-phenylethylammonium rac-hydrogen tartrate [(III), P21, Z′= 2] contain anion sheets built from four types of ring, R_2^2(10), R_2^2(12), R^4_2(14) and R_4^4(20), and there are cations pendent from both faces of the sheet. The anion substructure in bis[(S)-1-phenylethylammonium] (R,R)-tartrate [(IV), P21, Z′ = 1] consists of simple C(5) chains, which are linked into sheets by the cations, while in bis(rac-1-phenylethylammonium) (R,R)-tartrate [(V), P21, Z′ = 2] there are anion sheets containing two distinct types of R_4^4(22) ring, with equal numbers of (R) and (S) cations pendent from each face of the anion sheet. Bis[(R)-1-phenylethylammonium] rac-tartrate methanol hemisolvate [(VI), P1, Z′ = 4, with 14 independent components in the asymmetric unit] contains anion sheets built from two types of R_2^2(12) ring and two types of R_6^6(32) ring; half of the cations and half of the methanol molecules are pendent from each face of the sheet. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7681 Turkington, D.E. MacLean, E.J. Lough, A.J. Ferguson, G. Glidewell, C. 2005-02-01 doi:10.1107/S0108768104029684 International Union of Crystallography The supramolecular structures of three stereochemical forms of 1-phenylethylammonium hydrogen tartrate and three stereochemical forms of bis-1-phenylethylammonium tartrate are analysed in terms of their anion substructures. en SUPRAMOLECULAR STRUCTURES; HYDROGEN BONDING; GRAPH-SET ANALYSIS; TARTRATE SALTS The structures of six 1-phenylethylammonium tartrates have been determined and in each of them a distinctive hydrogen-bonded anion substructure can be identified. (S)-1-Phenyl­ethylammonium (R,R)-hydrogen tartrate [(I), P21, Z′ = 1] contains anion sheets built from a single type of R_4^4(22) ring with cations pendent, via three N—H⋯O hydrogen bonds, from just one face of the sheet. (S)-1-Phenylethylammonium rac-hydrogen tartrate [(II), P21, Z′ = 2] and its enantiomorph (R)-1-phenylethylammonium rac-hydrogen tartrate [(III), P21, Z′= 2] contain anion sheets built from four types of ring, R_2^2(10), R_2^2(12), R^4_2(14) and R_4^4(20), and there are cations pendent from both faces of the sheet. The anion substructure in bis[(S)-1-phenylethylammonium] (R,R)-tartrate [(IV), P21, Z′ = 1] consists of simple C(5) chains, which are linked into sheets by the cations, while in bis(rac-1-phenylethylammonium) (R,R)-tartrate [(V), P21, Z′ = 2] there are anion sheets containing two distinct types of R_4^4(22) ring, with equal numbers of (R) and (S) cations pendent from each face of the anion sheet. Bis[(R)-1-phenylethylammonium] rac-tartrate methanol hemisolvate [(VI), P1, Z′ = 4, with 14 independent components in the asymmetric unit] contains anion sheets built from two types of R_2^2(12) ring and two types of R_6^6(32) ring; half of the cations and half of the methanol molecules are pendent from each face of the sheet. text/html Supramolecular structures of 1-phenylethylammonium tartrates text 61 1 Copyright (c) 2005 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2005-02-01 103 research papers 0108-7681 med@iucr.org 114 1600-5740 http://scripts.iucr.org/cgi-bin/paper?ws5013 The crystal structures of eight new co-crystals of quinol with pyrazine, piperazine, morpholine, pyridine, piperidine, 4,4′-bipyridine, N-methylmorpholine and N,N′-dimethylpiperazine are reported. Quinol forms 1:1 co-crystals with pyrazine, piperazine and N,N′-dimethylpiperazine, but 1:2 co-crystals with morpholine, 4,4′-bipyridine, N-methylmorpholine, pyridine and piperidine. This difference can be rationalized in most cases by the presence of, respectively, two or one strong hydrogen-bond acceptor(s) in the guest molecule. The exception to this generalization is 4,4′-bipyridine, which forms a 1:2 co-crystal, possibly to optimize crystal packing. All structures are dominated by hydrogen bonding between quinol and the guest molecules. A doubly bridging motif, which connects pairs of quinol and guest molecules via NH⋯O or CH⋯O interactions, is present in all but the sterically hindered N,N′-dimethylpiperazine and N-methylmorpholine co-crystals. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7681 Oswald, I.D.H. Motherwell, W.D.S. Parsons, S. 2005-02-01 doi:10.1107/S0108768104028605 International Union of Crystallography The crystal structures of eight new co-crystals of quinol with simple hydrogen-bond acceptors are reported. All structures are dominated by hydrogen bonding between quinol and the guest molecules. A doubly bridging motif is present in all but two of the co-crystals. en QUINOL; HYDROGEN BONDING The crystal structures of eight new co-crystals of quinol with pyrazine, piperazine, morpholine, pyridine, piperidine, 4,4′-bipyridine, N-methylmorpholine and N,N′-dimethylpiperazine are reported. Quinol forms 1:1 co-crystals with pyrazine, piperazine and N,N′-dimethylpiperazine, but 1:2 co-crystals with morpholine, 4,4′-bipyridine, N-methylmorpholine, pyridine and piperidine. This difference can be rationalized in most cases by the presence of, respectively, two or one strong hydrogen-bond acceptor(s) in the guest molecule. The exception to this generalization is 4,4′-bipyridine, which forms a 1:2 co-crystal, possibly to optimize crystal packing. All structures are dominated by hydrogen bonding between quinol and the guest molecules. A doubly bridging motif, which connects pairs of quinol and guest molecules via NH⋯O or CH⋯O interactions, is present in all but the sterically hindered N,N′-dimethylpiperazine and N-methylmorpholine co-crystals. text/html Formation of quinol co-crystals with hydrogen-bond acceptors text 61 1 Copyright (c) 2005 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2005-02-01 46 research papers 0108-7681 med@iucr.org 57 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bm5015 A systematic study is reported of the products of the nucleophilic substitution reactions of the spermine-bridged cyclotriphosphazene, [N3P3X4(NHCH2CH2CH2N)CH2CH2]2 [where X = Cl (2a)], to give a number of new structures [(2b)–(2g)] in which X = OPh, [spiro-O(CH2)3O]0.5, Ph, NHPh, NC4H8 and NHBut, respectively. A comparison has been made between the sum of the substituent basicity constants, ΣαR, obtained in nitrobenzene solution, and ten molecular parameters of the N3P3 ring (the internal bond angles α, β, γ, δ and θ, and the P—N bond lengths a, b, c, d and e) as well as the difference between the bond lengths a and b, Δ(P—N). It is found that the systematic change in molecular parameters of compounds (2a)–(2g) is in line with changes in αR values, indicating the similarity in relative electron-releasing capacity of substituents X in the solid state and in solution. It is also found that the effect on molecular parameters of (2a)–(2g) with two X substituents in PX2 groups is greater than that for one X substituent in P(OR)X groups in an analogous series of compounds observed previously [Beşli et al. (2002). Acta Cryst. B58, 1067–1073]. Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7681 Coles, S.J. Davies, D.B. Hursthouse, M.B. Kiliç, A. Mayer, T.A. Shaw, R.A. Yenilmez Çiftçi, G. 2004-12-01 doi:10.1107/S0108768104025947 International Union of Crystallography The synthesis and crystal structures of six new per-substituted spermine-bridged cyclotriphosphazenes, [N3P3X4(NHCH2CH2CH2N)CH2CH2]2 (where X = OPh, [spiro-O(CH2)3O]0.5, Ph, NHPh, NC4H8 and NHBut, respectively) are reported and the observed relationship between molecular parameters of the N3P3 ring and substituent basicity constants is discussed. en PHOSPHORUS NITROGEN COMPOUNDS; SUBSTITUTED CYCLOPHOSPHAZENES; STRUCTURE PROPERTY RELATIONSHIPS A systematic study is reported of the products of the nucleophilic substitution reactions of the spermine-bridged cyclotriphosphazene, [N3P3X4(NHCH2CH2CH2N)CH2CH2]2 [where X = Cl (2a)], to give a number of new structures [(2b)–(2g)] in which X = OPh, [spiro-O(CH2)3O]0.5, Ph, NHPh, NC4H8 and NHBut, respectively. A comparison has been made between the sum of the substituent basicity constants, ΣαR, obtained in nitrobenzene solution, and ten molecular parameters of the N3P3 ring (the internal bond angles α, β, γ, δ and θ, and the P—N bond lengths a, b, c, d and e) as well as the difference between the bond lengths a and b, Δ(P—N). It is found that the systematic change in molecular parameters of compounds (2a)–(2g) is in line with changes in αR values, indicating the similarity in relative electron-releasing capacity of substituents X in the solid state and in solution. It is also found that the effect on molecular parameters of (2a)–(2g) with two X substituents in PX2 groups is greater than that for one X substituent in P(OR)X groups in an analogous series of compounds observed previously [Beşli et al. (2002). Acta Cryst. B58, 1067–1073]. text/html Structural investigations of phosphorus–nitrogen compounds. 6. Relationships between molecular parameters in per-X-substituted bridged spermine derivatives and basicity constants ΣαR of substituents text 60 6 Copyright (c) 2004 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2004-12-01 739 research papers 0108-7681 med@iucr.org 747 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bm5017 The geometry of the R_2^2(8) graph set formed between a 2-aminoheterocyclic ring containing an Nsp2 atom (in the 1-position of the ring) and a carboxylic acid has been studied. Collating data from known co-crystal structures containing five- and six-membered heterocyclic rings from the Cambridge Structural Database revealed unexpected differences between two kinds of non-hydrogen contact distances, and between specific bond distances and angles of the heterocycle. Not only were the interatomic non-hydrogen distances between the N atoms (heterocycle) and O atoms (carboxylate) asymmetric, but also the 2-amino N atom (N21) to the heterocyclic C atom (C2) bond was shorter than the C2 to N1sp2 bond. However, this shortening of the C2—N21 bond was not observed in the examples where N21 was substituted with a non-H atom. For the six-membered rings the data also showed that as the C2—N21 bond shortened the N1—C2—N21 bond angle increased. Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7681 Lynch, D.E. Jones, G.D. 2004-12-01 doi:10.1107/S0108768104023791 International Union of Crystallography The geometry of the R^2_2(8) graph set formed between a 2-aminoheterocyclic ring containing an Nsp2 atom (in the 1-position of the ring) and a carboxylic acid has been studied by collating data from known structures from the CSD. Unexpected differences were found to occur between both the non-hydrogen contact distances, and specific bond distances and angles of the heterocycle. en HYDROGEN BONDS; 2-AMINOPYRIMIDINE; CARBOXYLIC ACID; R_2^2(8) GRAPH SET; 2-AMINOTHIAZOLE The geometry of the R_2^2(8) graph set formed between a 2-aminoheterocyclic ring containing an Nsp2 atom (in the 1-position of the ring) and a carboxylic acid has been studied. Collating data from known co-crystal structures containing five- and six-membered heterocyclic rings from the Cambridge Structural Database revealed unexpected differences between two kinds of non-hydrogen contact distances, and between specific bond distances and angles of the heterocycle. Not only were the interatomic non-hydrogen distances between the N atoms (heterocycle) and O atoms (carboxylate) asymmetric, but also the 2-amino N atom (N21) to the heterocyclic C atom (C2) bond was shorter than the C2 to N1sp2 bond. However, this shortening of the C2—N21 bond was not observed in the examples where N21 was substituted with a non-H atom. For the six-membered rings the data also showed that as the C2—N21 bond shortened the N1—C2—N21 bond angle increased. text/html Geometry of the 2-aminoheterocyclic–carboxylic acid R22(8) graph set: implications for crystal engineering text 60 6 Copyright (c) 2004 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2004-12-01 748 research papers 0108-7681 med@iucr.org 754 1600-5740 http://scripts.iucr.org/cgi-bin/paper?ws5020 The scheme of structures shown in Fig. 1 of the paper by Howard & Zhang (2004) is incomplete. Structures corresponding to different tilt systems, allowing but not requiring the layered ordering of A-site cations, were inadvertently omitted. The corrected version of this schematic is shown by Howard & Stokes (2004) as their Fig. 5. The additional structures can be shown to be unsuitable as candidate structures for the compounds considered by Howard & Zhang, so the arguments used by Howard & Zhang (2004) for structure identification remain unaffected. Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7681 Howard, C.J. Zhang, Z. 2004-12-01 doi:10.1107/S010876810402186X International Union of Crystallography Erratum to Acta Cryst. B60, 249–251. en PEROVSKITES; LAYERED ORDERING; OCTAHEDRAL TILTING The scheme of structures shown in Fig. 1 of the paper by Howard & Zhang (2004) is incomplete. Structures corresponding to different tilt systems, allowing but not requiring the layered ordering of A-site cations, were inadvertently omitted. The corrected version of this schematic is shown by Howard & Stokes (2004) as their Fig. 5. The additional structures can be shown to be unsuitable as candidate structures for the compounds considered by Howard & Zhang, so the arguments used by Howard & Zhang (2004) for structure identification remain unaffected. text/html Structure for perovskites with layered ordering of A-site cations. Erratum text 60 6 Copyright (c) 2004 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2004-12-01 763 addenda and errata 0108-7681 med@iucr.org 763 1600-5740 http://scripts.iucr.org/cgi-bin/paper?de5008 The crystal structures of the 3-halopyridinium hexachloroplatinate(IV) dihydrates (HPyX-3)2[PtCl6]·2H2O [(1), X = Br; (2a), (2b), X = I] comprise networks in which the molecular components are linked via N—H⋯O and O—H⋯Cl—Pt hydrogen bonds and Pt—Cl⋯X—C halogen bonds (X = Br, I). The iodo derivative has been isolated in two polymorphic forms. Of particular interest to the understanding of the utility of the hydrogen bonds and M—X⋯X′—C halogen bonds that propagate the networks in anhydrous salts of this type is that the water molecules insert exclusively into the putative N—H⋯Cl—Pt hydrogen bonds, while the Pt—Cl⋯X′—C halogen bonds remain undisrupted by the presence of water molecules. Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7681 Zordan, F. Brammer, L. 2004-10-01 doi:10.1107/S0108768104016064 International Union of Crystallography Crystals of the dihydrates of three halopyridinium hexachloroplatinate salts form networks that are propagated via N—H⋯O and O—H⋯Cl—Pt hydrogen bonds and Pt—Cl⋯X—C halogen bonds. The water molecules can be considered to have been inserted into N—H⋯Cl—Pt hydrogen bonds anticipated in the anyhdrous form of such salts. en HYDROGEN BONDS; HALOGEN BONDS; POLYMORPHS; HALOPYRIDINIUM HEXACHLOROPLATINATES The crystal structures of the 3-halopyridinium hexachloroplatinate(IV) dihydrates (HPyX-3)2[PtCl6]·2H2O [(1), X = Br; (2a), (2b), X = I] comprise networks in which the molecular components are linked via N—H⋯O and O—H⋯Cl—Pt hydrogen bonds and Pt—Cl⋯X—C halogen bonds (X = Br, I). The iodo derivative has been isolated in two polymorphic forms. Of particular interest to the understanding of the utility of the hydrogen bonds and M—X⋯X′—C halogen bonds that propagate the networks in anhydrous salts of this type is that the water molecules insert exclusively into the putative N—H⋯Cl—Pt hydrogen bonds, while the Pt—Cl⋯X′—C halogen bonds remain undisrupted by the presence of water molecules. text/html Water molecules insert into N—H⋯Cl—M hydrogen bonds while M—Cl⋯X—C halogen bonds remain intact in dihydrates of halopyridinium hexachloroplatinates text 60 5 Copyright (c) 2004 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2004-10-01 512 research papers 0108-7681 med@iucr.org 519 1600-5740 http://scripts.iucr.org/cgi-bin/paper?na5018 Molecules of 2-iodo-N-(4-nitrobenzyl)aniline, 4-O2NC6H4CH2NHC6H4I-2′ (1) are linked into chains by C—H⋯O hydrogen bonds. In the isomeric compound 3-iodo-N-(4-nitrobenzyl)aniline (2) a combination of N—H⋯O and C—H⋯O hydrogen bonds and iodo⋯nitro and aromatic π⋯π stacking interactions links the molecules into a three-dimensional framework structure. The two-dimensional supramolecular structure of 4-iodo-N-(4-nitrobenzyl)aniline (6) is built from a combination of C—H⋯O and N—H⋯π(arene) hydrogen bonds and aromatic π⋯π stacking interactions. 2-Iodo-N-(2-nitrobenzyl)aniline (7) crystallizes with two molecules in the asymmetric unit and these molecules are linked into ladders by a combination of N—H⋯O and C—H⋯O hydrogen bonds and iodo⋯nitro and aromatic π⋯π stacking interactions. Comparisons are made between the supramolecular structures of these compounds and those of other isomers, in terms both of the types of direction-specific intermolecular interactions exhibited and the dimensionality of the resulting supramolecular structures. Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7681 Glidewell, C. Low, J.N. Skakle, J.M.S. Wardell, S.M.S.V. Wardell, J.L. 2004-08-01 doi:10.1107/S0108768104012017 International Union of Crystallography Iodo-N-(nitrobenzyl)anilines, O2NC6H4CH2NHC6H4I, can exhibit hydrogen bonds of four types, N—H⋯O, C—H⋯O, N—H⋯π(arene) and C—H⋯π(arene), as well as iodo⋯nitro and aromatic π⋯π stacking interactions. The resulting supramolecular structures can be one-, two- or three-dimensional. en HYDROGEN BONDING; STACKING INTERACTIONS; DIMENSIONALITY; SUPRAMOLECULAR STRUCTURES Molecules of 2-iodo-N-(4-nitrobenzyl)aniline, 4-O2NC6H4CH2NHC6H4I-2′ (1) are linked into chains by C—H⋯O hydrogen bonds. In the isomeric compound 3-iodo-N-(4-nitrobenzyl)aniline (2) a combination of N—H⋯O and C—H⋯O hydrogen bonds and iodo⋯nitro and aromatic π⋯π stacking interactions links the molecules into a three-dimensional framework structure. The two-dimensional supramolecular structure of 4-iodo-N-(4-nitrobenzyl)aniline (6) is built from a combination of C—H⋯O and N—H⋯π(arene) hydrogen bonds and aromatic π⋯π stacking interactions. 2-Iodo-N-(2-nitrobenzyl)aniline (7) crystallizes with two molecules in the asymmetric unit and these molecules are linked into ladders by a combination of N—H⋯O and C—H⋯O hydrogen bonds and iodo⋯nitro and aromatic π⋯π stacking interactions. Comparisons are made between the supramolecular structures of these compounds and those of other isomers, in terms both of the types of direction-specific intermolecular interactions exhibited and the dimensionality of the resulting supramolecular structures. text/html Isomeric iodo-N-(nitrobenzyl)anilines: interplay of hard and soft hydrogen bonds, iodo⋯nitro interactions and aromatic π⋯π stacking interactions text 60 4 Copyright (c) 2004 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2004-08-01 472 research papers 0108-7681 med@iucr.org 480 1600-5740 http://scripts.iucr.org/cgi-bin/paper?na5016 The structures of five substituted α,α′-trehalose trehalose derivatives have been determined, and these are compared with those of four previously published analogues. In 2,2′,3,3′,4,4′-hexaacetato-6,6′-bis-O-methylsulfonyl-α,α′-trehalose, C26H38O21S2, where the molecules lie across twofold rotation axes in the space group C2, a single C—H⋯O=S hydrogen bond links the molecules into sheets. 2,2′,3,3′,4,4′-Hexaacetato-6,6′-bis-O-(4-toluenesulfonyl)-α,α′-trehalose, C38H46O21S2, crystallizes with Z′ = 2 in the space group P212121 and a combination of three C—H⋯O hydrogen bonds, each having a carbonyl O atom as an acceptor, and a C—H⋯π(arene) hydrogen bond link the molecules into a three-dimensional framework. 2,2′,3,3′,4,4′-Hexaacetato-6,6′-diazido-α,α′-trehalose, C24H32N6O15, crystallizes as a partial ethanol solvate and three C—H⋯O hydrogen bonds link the substituted trehalose molecules into a three-dimensional framework. In 2,2′,3,3′-tetraacetato-6,6′-bis(N-acetylamino)-α,α′-trehalose dihydrate, C24H36N2O15·2H2O, the substituted trehalose molecules lie across twofold rotation axes in the space group P21212 and a three-dimensional framework is generated by the combination of O—H⋯O and N—H⋯O hydrogen bonds. The diaminotrehalose molecules in 6,6′-diamino-α,α′-trehalose dihydrate, C12H24N2O9.2(H2O), lie across twofold rotation axes in the space group P43212: a single O—H⋯N hydrogen bond links the trehalose molecules into sheets, which are linked into a three-dimensional framework by O—H⋯O hydrogen bonds. Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7681 Baddeley, T.C. Davidson, I.G. Glidewell, C. Low, J.N. Skakle, J.M.S. Wardell, J.L. 2004-08-01 doi:10.1107/S0108768104010912 International Union of Crystallography Hard and soft hydrogen bonds in substituted trehalose derivatives generate supramolecular structures in one, two and three dimensions. en TREHALOSE DERIVATIVES; HYDROGEN BONDING; SUPRAMOLECULAR STRUCTURES The structures of five substituted α,α′-trehalose trehalose derivatives have been determined, and these are compared with those of four previously published analogues. In 2,2′,3,3′,4,4′-hexaacetato-6,6′-bis-O-methylsulfonyl-α,α′-trehalose, C26H38O21S2, where the molecules lie across twofold rotation axes in the space group C2, a single C—H⋯O=S hydrogen bond links the molecules into sheets. 2,2′,3,3′,4,4′-Hexaacetato-6,6′-bis-O-(4-toluenesulfonyl)-α,α′-trehalose, C38H46O21S2, crystallizes with Z′ = 2 in the space group P212121 and a combination of three C—H⋯O hydrogen bonds, each having a carbonyl O atom as an acceptor, and a C—H⋯π(arene) hydrogen bond link the molecules into a three-dimensional framework. 2,2′,3,3′,4,4′-Hexaacetato-6,6′-diazido-α,α′-trehalose, C24H32N6O15, crystallizes as a partial ethanol solvate and three C—H⋯O hydrogen bonds link the substituted trehalose molecules into a three-dimensional framework. In 2,2′,3,3′-tetraacetato-6,6′-bis(N-acetylamino)-α,α′-trehalose dihydrate, C24H36N2O15·2H2O, the substituted trehalose molecules lie across twofold rotation axes in the space group P21212 and a three-dimensional framework is generated by the combination of O—H⋯O and N—H⋯O hydrogen bonds. The diaminotrehalose molecules in 6,6′-diamino-α,α′-trehalose dihydrate, C12H24N2O9.2(H2O), lie across twofold rotation axes in the space group P43212: a single O—H⋯N hydrogen bond links the trehalose molecules into sheets, which are linked into a three-dimensional framework by O—H⋯O hydrogen bonds. text/html Supramolecular structures of substituted α,α′-trehalose derivatives text 60 4 Copyright (c) 2004 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2004-08-01 461 research papers 0108-7681 med@iucr.org 471 1600-5740 http://scripts.iucr.org/cgi-bin/paper?av5005 The crystal structures of piperazine, piperidine and morpholine have been determined at 150 K. All three structures are characterized by the formation of NH⋯N hydrogen-bonded chains. In piperazine these are linked to form sheets, but the chains are shifted so that the molecules interleave. In morpholine there are in addition weak CH⋯O interactions. Topological analyses show that these three structures are closely related to that of cyclohexane-II, which can be described in terms of a pseudo-cubic close-packed array of molecules in a familiar ABC layered arrangement. While the positions of the molecules within each layer are similar, hydrogen bonding occurs between the ABC layers and in order to accommodate this the molecules are rotated relative to those in cyclohexane-II. Piperidine and morpholine also adopt layered structures, with hydrogen-bonding or CH⋯O interactions between the layers. In these cases, however, the layering more resembles a hexagonal close-packed arrangement. Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7681 Parkin, A. Oswald, I.D.H. Parsons, S. 2004-04-01 doi:10.1107/S0108768104003672 International Union of Crystallography The crystal structures of piperazine, piperidine and morpholine have been determined at 150 K. All three structures are characterized by the formation of NH⋯N hydrogen-bonded chains. In piperazine these are linked to form sheets, but the chains are shifted so that the molecules interleave. In morpholine there are in addition weak CH⋯O interactions. Packing in these three structures is compared to that observed in cyclohexane. en HYDROGEN-BONDED CHAINS; PACKING The crystal structures of piperazine, piperidine and morpholine have been determined at 150 K. All three structures are characterized by the formation of NH⋯N hydrogen-bonded chains. In piperazine these are linked to form sheets, but the chains are shifted so that the molecules interleave. In morpholine there are in addition weak CH⋯O interactions. Topological analyses show that these three structures are closely related to that of cyclohexane-II, which can be described in terms of a pseudo-cubic close-packed array of molecules in a familiar ABC layered arrangement. While the positions of the molecules within each layer are similar, hydrogen bonding occurs between the ABC layers and in order to accommodate this the molecules are rotated relative to those in cyclohexane-II. Piperidine and morpholine also adopt layered structures, with hydrogen-bonding or CH⋯O interactions between the layers. In these cases, however, the layering more resembles a hexagonal close-packed arrangement. text/html Structures of piperazine, piperidine and morpholine text 60 2 Copyright (c) 2004 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2004-04-01 219 research papers 0108-7681 med@iucr.org 227 1600-5740 http://scripts.iucr.org/cgi-bin/paper?na5012 The structures of five hydrogen-bonded adducts of triphenylsilanol, Ph3SiOH, with diamines have been determined. In the 4:1 adduct formed with 1,4-diazabicyclo[2.2.2]octane, (Ph3SiOH)4·C6H12N2 (I) (triclinic, P\bar 1, Z′ = 2), there are two independent five-component aggregates built from O—H⋯N and O—H⋯O hydrogen bonds, in one of which the diamine exhibits orientational disorder: these two aggregates are linked into a cyclic ten-molecule unit by means of two independent C—H⋯π(arene) hydrogen bonds. The 4:1 adduct formed with 1,2-bis(4-pyridyl)ethene, (Ph3SiOH)4·C12H10N2 (II) (triclinic, P\bar 1, Z′ = 0.5), forms a similar five-component aggregate which lies across a centre of inversion: a single C—H⋯π(arene) hydrogen bond links these aggregates into a molecular ladder. With N,N′-dimethylpiperazine, triphenylsilanol forms a 2:1 adduct, (Ph3SiOH)2·C6H14N2 (III) (monoclinic, P21/c, Z′ = 0.5), in which a three-component aggregate built from O—H⋯N hydrogen bonds lies across a centre of inversion: two independent C—H⋯π(arene) hydrogen bonds link these aggregates into sheets. In the hydrated 2:1 adduct formed with 1,2-bis(4′-bipyridyl)ethane, (Ph3SiOH)2·C12H12N2·H2O (IV) (triclinic, P\bar 1, Z′ = 1), a combination of two independent O—H⋯O and two independent N—H⋯O hydrogen bonds links the five molecular components into a centrosymmetric eight-molecule aggregate, and six independent C—H⋯π(arene) hydrogen bonds link these chains into a continuous three-dimensional framework structure. In the dihydrated 2:1 adduct formed with 4,4′-bipyridyl, (Ph3SiOH)2·C10H8N2·(H2O)2 (V) (triclinic, P\bar 1, Z′ = 1), a combination of four independent O—H⋯O and two independent N—H⋯O hydrogen bonds links the five molecular components into a chain of rings, and four independent C—H⋯π(arene) hydrogen bonds link these chains into a continuous three-dimensional framework structure. Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7681 Turkington, D.E. Lough, A.J. Ferguson, G. Glidewell, C. 2004-04-01 doi:10.1107/S0108768104002344 International Union of Crystallography Hydrogen-bonded adducts of triphenylsilanol, Ph3SiOH, with organic diamines form supramolecular structures containing isolated (zero-dimensional) aggregates or continuous structures in the form of a chain (one-dimensional), a sheet (two-dimensional) or a framework (three-dimensional). en HYDROGEN BONDING; SUPRAMOLECULAR STRUCTURES The structures of five hydrogen-bonded adducts of triphenylsilanol, Ph3SiOH, with diamines have been determined. In the 4:1 adduct formed with 1,4-diazabicyclo[2.2.2]octane, (Ph3SiOH)4·C6H12N2 (I) (triclinic, P\bar 1, Z′ = 2), there are two independent five-component aggregates built from O—H⋯N and O—H⋯O hydrogen bonds, in one of which the diamine exhibits orientational disorder: these two aggregates are linked into a cyclic ten-molecule unit by means of two independent C—H⋯π(arene) hydrogen bonds. The 4:1 adduct formed with 1,2-bis(4-pyridyl)ethene, (Ph3SiOH)4·C12H10N2 (II) (triclinic, P\bar 1, Z′ = 0.5), forms a similar five-component aggregate which lies across a centre of inversion: a single C—H⋯π(arene) hydrogen bond links these aggregates into a molecular ladder. With N,N′-dimethylpiperazine, triphenylsilanol forms a 2:1 adduct, (Ph3SiOH)2·C6H14N2 (III) (monoclinic, P21/c, Z′ = 0.5), in which a three-component aggregate built from O—H⋯N hydrogen bonds lies across a centre of inversion: two independent C—H⋯π(arene) hydrogen bonds link these aggregates into sheets. In the hydrated 2:1 adduct formed with 1,2-bis(4′-bipyridyl)ethane, (Ph3SiOH)2·C12H12N2·H2O (IV) (triclinic, P\bar 1, Z′ = 1), a combination of two independent O—H⋯O and two independent N—H⋯O hydrogen bonds links the five molecular components into a centrosymmetric eight-molecule aggregate, and six independent C—H⋯π(arene) hydrogen bonds link these chains into a continuous three-dimensional framework structure. In the dihydrated 2:1 adduct formed with 4,4′-bipyridyl, (Ph3SiOH)2·C10H8N2·(H2O)2 (V) (triclinic, P\bar 1, Z′ = 1), a combination of four independent O—H⋯O and two independent N—H⋯O hydrogen bonds links the five molecular components into a chain of rings, and four independent C—H⋯π(arene) hydrogen bonds link these chains into a continuous three-dimensional framework structure. text/html Hydrogen-bonded adducts of triphenylsilanol with diamines: a finite ten-molecule aggregate, and chain, sheet and framework structures built from O—H⋯O, O—H⋯N and C—H⋯π(arene) hydrogen bonds text 60 2 Copyright (c) 2004 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2004-04-01 238 research papers 0108-7681 med@iucr.org 248 1600-5740 http://scripts.iucr.org/cgi-bin/paper?ck5001 Incommensurately modulated ammonium tetrafluoroberyllate (AFB) occurs in a narrow temperature interval between the paraelectric room-temperature phase with space group Pnma (Ti = 178 K) and the ferroelectric low-temperature phase with space group Pna21 (Tc = 173 K). The structure is determined from accurate single-crystal X-ray diffraction data collected with synchrotron radiation at 175 K. The superspace group of the structure is Pnma(α00)0ss with α = 0.4796 (4). Both structure refinements and the maximum entropy method lead to the same structure model, which involves only single harmonic modulations. The building units of the structure are BeF_4^{2-} and NH_4^+ complex ions with approximately tetrahedral point symmetry. They are relatively rigid and the modulations consist mainly of translations of the tetrahedra and their rotations around a fixed axis. The modulation is related to changes in the network of the hydrogen bonds. The low-temperature superstructure can be described as a commensurately modulated structure with the same superspace symmetry. The first harmonic modulations of the low-temperature and incommensurate phases are related by a scale factor with a value of approximately two. In addition, the low-temperature phase exhibits a second harmonic modulation that is responsible for shifts along c and the ferroelectricity in this phase. The experimental data of the incommensurate phase do not contain any evidence for the presence of a second harmonic in the modulation functions. This suggests that the development of the second harmonic, i.e. the development of the spontaneous polarization, is responsible for the lock-in transition. Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7681 Palatinus, L. Amami, M. van Smaalen, S. 2004-04-01 doi:10.1107/S0108768104000874 International Union of Crystallography The incommensurately modulated structure of ammonium fluoroberyllate is found to result from correlated rotations and displacements of the rigid complex ions according to a first harmonic modulation wave. The resulting changes in the network of the hydrogen bonds lead to the stabilization of the structure. en INCOMMENSURATE MODULATION; SUPERSPACE; MAXIMUM ENTROPY METHOD Incommensurately modulated ammonium tetrafluoroberyllate (AFB) occurs in a narrow temperature interval between the paraelectric room-temperature phase with space group Pnma (Ti = 178 K) and the ferroelectric low-temperature phase with space group Pna21 (Tc = 173 K). The structure is determined from accurate single-crystal X-ray diffraction data collected with synchrotron radiation at 175 K. The superspace group of the structure is Pnma(α00)0ss with α = 0.4796 (4). Both structure refinements and the maximum entropy method lead to the same structure model, which involves only single harmonic modulations. The building units of the structure are BeF_4^{2-} and NH_4^+ complex ions with approximately tetrahedral point symmetry. They are relatively rigid and the modulations consist mainly of translations of the tetrahedra and their rotations around a fixed axis. The modulation is related to changes in the network of the hydrogen bonds. The low-temperature superstructure can be described as a commensurately modulated structure with the same superspace symmetry. The first harmonic modulations of the low-temperature and incommensurate phases are related by a scale factor with a value of approximately two. In addition, the low-temperature phase exhibits a second harmonic modulation that is responsible for shifts along c and the ferroelectricity in this phase. The experimental data of the incommensurate phase do not contain any evidence for the presence of a second harmonic in the modulation functions. This suggests that the development of the second harmonic, i.e. the development of the spontaneous polarization, is responsible for the lock-in transition. text/html Structure of incommensurate ammonium tetrafluoroberyllate studied by structure refinements and the maximum entropy method text 60 2 Copyright (c) 2004 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2004-04-01 127 research papers 0108-7681 med@iucr.org 137 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bk9135 The alignment in Tables 1–4 of the paper by Abrahams (2003) was incorrect. The corrected tables are reproduced herein. Copyright (c) 2003 International Union of Crystallography urn:issn:0108-7681 Abrahams, S.C. 2003-12-01 doi:10.1107/S0108768103021840 International Union of Crystallography An erratum to the paper by Abrahams (2003). Acta Cryst. B59, 541–556. en The alignment in Tables 1–4 of the paper by Abrahams (2003) was incorrect. The corrected tables are reproduced herein. text/html Systematic prediction of new ferroelectrics in space groups P31 and P32. Erratum text 59 6 Copyright (c) 2003 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2003-12-01 811 addenda and errata 0108-7681 med@iucr.org 813 1600-5740 http://scripts.iucr.org/cgi-bin/paper?bs9019 A value is missing in the third row of the O3—C3 section of Table 3 on p. 238 of Farrugia et al. (2003). The missing value which should be in the fifth column is 13.757, and the remaining entries should be transfered to the next column along. Copyright (c) 2003 International Union of Crystallography urn:issn:0108-7681 Farrugia, L.J. Mallinson, P.R. Stewart, B. 2003-06-01 doi:10.1107/S0108768103007389 International Union of Crystallography An erratum to the paper by Farrugia et al. (2003). Acta Cryst. B59, 234–247. en CHARGE DENSITY; TRANSITION METAL; COMPARATIVE STUDY; TOPOLOGICAL ANALYSIS; BOND CRITICAL POINTS A value is missing in the third row of the O3—C3 section of Table 3 on p. 238 of Farrugia et al. (2003). The missing value which should be in the fifth column is 13.757, and the remaining entries should be transfered to the next column along. text/html Experimental charge density in the transition metal complex Mn2(CO)10: a comparative study. Erratum text 59 3 Copyright (c) 2003 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2003-06-01 428 addenda and errata 0108-7681 med@iucr.org 428 1600-5740 http://scripts.iucr.org/cgi-bin/paper?lc9053 Owing to a printers' error in the paper by Munshi & Guru Row [ Acta Cryst. (2002), B58, 1011–1017], Figs. 4(a) and 4(b) on page 1015 were transposed. Revised PDF versions of these pages are available in the online version of this erratum, which is available through Crystallography Journals Online. Copyright (c) 2003 International Union of Crystallography urn:issn:0108-7681 Munshi, P. Guru Row, T.N. 2003-02-01 doi:10.1107/S0108768103001666 International Union of Crystallography Erratum to Acta Cryst. (2002), B58, 1011–1017. en EXPERIMENTAL ELECTRON DENSITY; 2H-CHROMENE-2-THIONE; MULTIPOLE MODEL Owing to a printers' error in the paper by Munshi & Guru Row [ Acta Cryst. (2002), B58, 1011–1017], Figs. 4(a) and 4(b) on page 1015 were transposed. Revised PDF versions of these pages are available in the online version of this erratum, which is available through Crystallography Journals Online. text/html Electron density study of 2H-chromene-2-thione text 59 1 Copyright (c) 2003 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2003-02-01 159 addenda and errata 0108-7681 med@iucr.org 159 1600-5740 http://scripts.iucr.org/cgi-bin/paper?ws9067 A replacement Fig. 6 to the paper by Ibberson et al. (2008), Acta Cryst. B64, 573–582 is given. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7681 Ibberson, R.M. Parsons, S. Allan, D.R. Bell, A.M.T. 2008-12-01 doi:10.1107/S0108768108036197 International Union of Crystallography A corrigendum to the paper by Ibberson et al. (2008), Acta Cryst. B64, 573–582. en NEUTRON POWDER DIFFRACTION; LOW-TEMPERATURE CRYSTALLOGRAPHY; HYDROGEN BONDING; PHASE TRANSITIONS A replacement Fig. 6 to the paper by Ibberson et al. (2008), Acta Cryst. B64, 573–582 is given. text/html Polymorphism in cyclohexanol. Corrigendum text 64 6 Copyright (c) 2008 International Union of Crystallography Acta Crystallographica Section B: Structural Science 2008-12-01 791 addenda and errata 0108-7681 med@iucr.org 791 1600-5740