http://journals.iucr.org/b/issues/2009/06/00/isscontsbdy.html Acta Crystallographica Section B: Structural Science publishes papers in which structure is the primary focus of the work reported. The central themes of Structural Science are the acquisition of structural knowledge from novel experimental observations or from existing data, the correlation of structural knowledge with physico-chemical and other properties, and the application of this knowledge to solve problems in the structural domain. Structural Science has broad chemical coverage, encompassing metals and alloys, inorganics and minerals, metal-organics and purely organic compounds. en Copyright (c) 2009 International Union of Crystallography 2009-12-01 International Union of Crystallography International Union of Crystallography http://journals.iucr.org urn:issn:0108-7681 Acta Crystallographica Section B: Structural Science publishes papers in which structure is the primary focus of the work reported. The central themes of Structural Science are the acquisition of structural knowledge from novel experimental observations or from existing data, the correlation of structural knowledge with physico-chemical and other properties, and the application of this knowledge to solve problems in the structural domain. Structural Science has broad chemical coverage, encompassing metals and alloys, inorganics and minerals, metal-organics and purely organic compounds. text/html Acta Crystallographica Section B: Structural Science, Volume 65, Part 6, 2009 text yearly 6 2002-02-01T00:00+00:00 6 65 2009-12-01 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science 659 urn:issn:0108-7681 med@iucr.org December 2009 2009-12-01 http://journals.iucr.org/logos/rss10b.gif http://journals.iucr.org/b/issues/2009/06/00/isscontsbdy.html Still image http://scripts.iucr.org/cgi-bin/paper?bp5023 Oriented single crystals of the high-temperature phase of KNO3 (phase III), a ferroelectric compound that may also occur as an atmospheric aerosol particle, were grown at room temperature and pressure by atomizing a solution of KNO3 in water and allowing droplets to dry on a glass substrate. The crystals are up to 1 mm across and are stable unless mechanically disturbed. There is no evidence of the spontaneous transformation of phase III to the room-temperature stable phase (phase II), even after several months. Single-crystal structure determinations of phase III were obtained at 295 and 123 K. The unit cell regained its room-temperature dimensions after warming from 123 K. The phase-III KNO3 structure can be viewed as the stacking parallel to the c axis of alternating K atoms and planar NO3 groups. The NO3 groups connect the planes of K atoms, where each O is fourfold coordinated to one N and three K. Each K atom has nine O nearest neighbors, with three bonds at 2.813 and six at 2.9092 Å. The interatomic K—N—K distance alternates from 5.051 to 3.941 along the c axis. The N—O distances increase from 1.245 (2) Å at 295 K to 1.2533 (15) Å at 123 K. The nitrate group has a slight non-planarity, with the N atoms 0.011 Å above the O plane and directed toward the more distant K of the K—N—K chain. Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Freney, E.J. Garvie, L.A.J. Groy, T.L. Buseck, P.R. 2009-11-16 doi:10.1107/S0108768109041019 International Union of Crystallography This paper describes a novel method for the room-temperature growth of single crystals of phase-III KNO3 and refines its structure at both room temperature and 123 K. en aerosol particles explosives propellants polymorphism Oriented single crystals of the high-temperature phase of KNO3 (phase III), a ferroelectric compound that may also occur as an atmospheric aerosol particle, were grown at room temperature and pressure by atomizing a solution of KNO3 in water and allowing droplets to dry on a glass substrate. The crystals are up to 1 mm across and are stable unless mechanically disturbed. There is no evidence of the spontaneous transformation of phase III to the room-temperature stable phase (phase II), even after several months. Single-crystal structure determinations of phase III were obtained at 295 and 123 K. The unit cell regained its room-temperature dimensions after warming from 123 K. The phase-III KNO3 structure can be viewed as the stacking parallel to the c axis of alternating K atoms and planar NO3 groups. The NO3 groups connect the planes of K atoms, where each O is fourfold coordinated to one N and three K. Each K atom has nine O nearest neighbors, with three bonds at 2.813 and six at 2.9092 Å. The interatomic K—N—K distance alternates from 5.051 to 3.941 along the c axis. The N—O distances increase from 1.245 (2) Å at 295 K to 1.2533 (15) Å at 123 K. The nitrate group has a slight non-planarity, with the N atoms 0.011 Å above the O plane and directed toward the more distant K of the K—N—K chain. text/html Growth and single-crystal refinement of phase-III potassium nitrate, KNO3 text 6 65 2009-11-16 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 659 663 http://scripts.iucr.org/cgi-bin/paper?bp5024 Synthetic Co2SiO4 crystallizes in the olivine structure (space group Pnma) with two crystallographically non-equivalent Co positions and shows antiferromagnetic ordering below 50 K. We have investigated the temperature variation of the Co2SiO4 magnetic structure by means of non-polarized and polarized neutron diffraction for single crystals. Measurements with non-polarized neutrons were made at 2.5 K (below TN), whereas polarized neutron diffraction experiments were carried out at 70 and 150 K (above TN) in an external magnetic field of 7 T parallel to the b axis. Additional accurate non-polarized powder diffraction studies were performed in a broad temperature range from 5 to 500 K with small temperature increments. Detailed symmetry analysis of the Co2SiO4 magnetic structure shows that it corresponds to the magnetic (Shubnikov) group Pnma, which allows the antiferromagnetic configuration (Gx, Cy, Az) for the 4a site with inversion symmetry \bar{1} (Co1 position) and (0,Cy,0) for the 4c site with mirror symmetry m (Co2 position). The temperature dependence of the Co1 and Co2 magnetic moments obtained from neutron diffraction experiments was fitted in a modified molecular-field model. The polarized neutron study of the magnetization induced by an applied field shows a non-negligible amount of magnetic moment on the oxygen positions, indicating a delocalization of the magnetic moment from Co towards neighbouring O owing to superexchange coupling. The relative strength of the exchange interactions is discussed based on the non-polarized and polarized neutron data. Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Sazonov, A. Meven, M. Hutanu, V. Heger, G. Hansen, T. Gukasov, A. 2009-11-16 doi:10.1107/S0108768109042499 International Union of Crystallography The magnetic structure of the synthetic cobalt olivine, Co2SiO4, is determined by means of non-polarized and polarized neutron diffraction on single-crystal and powder samples. en magnetic behaviour polarized neutron data symmetry Synthetic Co2SiO4 crystallizes in the olivine structure (space group Pnma) with two crystallographically non-equivalent Co positions and shows antiferromagnetic ordering below 50 K. We have investigated the temperature variation of the Co2SiO4 magnetic structure by means of non-polarized and polarized neutron diffraction for single crystals. Measurements with non-polarized neutrons were made at 2.5 K (below TN), whereas polarized neutron diffraction experiments were carried out at 70 and 150 K (above TN) in an external magnetic field of 7 T parallel to the b axis. Additional accurate non-polarized powder diffraction studies were performed in a broad temperature range from 5 to 500 K with small temperature increments. Detailed symmetry analysis of the Co2SiO4 magnetic structure shows that it corresponds to the magnetic (Shubnikov) group Pnma, which allows the antiferromagnetic configuration (Gx, Cy, Az) for the 4a site with inversion symmetry \bar{1} (Co1 position) and (0,Cy,0) for the 4c site with mirror symmetry m (Co2 position). The temperature dependence of the Co1 and Co2 magnetic moments obtained from neutron diffraction experiments was fitted in a modified molecular-field model. The polarized neutron study of the magnetization induced by an applied field shows a non-negligible amount of magnetic moment on the oxygen positions, indicating a delocalization of the magnetic moment from Co towards neighbouring O owing to superexchange coupling. The relative strength of the exchange interactions is discussed based on the non-polarized and polarized neutron data. text/html Magnetic behaviour of synthetic Co2SiO4 text 6 65 2009-11-16 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 664 675 http://scripts.iucr.org/cgi-bin/paper?hw5005 A combination of selected-area electron diffraction (SAED), neutron powder diffraction (NPD) and high-resolution transmission electron microscopy (HRTEM) reveals a complex superstructure in the ordered perovskite NaLaMgWO6. Through indexing of SAED patterns the unit-cell dimensions are found to be 46.8 × 7.8 × 7.9 Å, which corresponds to a 12ap × 2ap × 2ap superstructure of the simple Pm\overline 3 m perovskite unit cell. HRTEM images reveal the formation of an unmistakable stripe contrast that repeats with the same periodicity. Doubling of the b and c axes is brought about by a combination of layered ordering of Na and La, rock-salt ordering of Mg and W, and octahedral tilting. The a axis repeat distance results from a one-dimensional twinning of the octahedral tilts in combination with a compositional modulation. Modeling of the NPD pattern shows that the underlying tilt system is a−a−c0 with tilt angles of ∼ 8° about the a and b axes. The octahedral tilt-twin boundaries run perpendicular to the a axis and are separated by 6ap. Simulated HRTEM images show that octahedral tilt twinning alone cannot explain the stripes seen in the HRTEM images, rather a compositional modulation involving the A-site cations is necessary to explain the experimental images. Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 King, G. Garcia-Martin, S. Woodward, P.M. 2009-10-27 doi:10.1107/S0108768109032728 International Union of Crystallography Neutron powder diffraction and transmission electron microscopy studies reveal that the ordered perovskite NaLaMgWO6 has a complex superstructure consisting of a compositional modulation of the A-site cations accompanied by a one-dimensional twinning of the octahedral tilt system. en twinning modulation neutron powder diffraction electron diffraction electron microscopy A combination of selected-area electron diffraction (SAED), neutron powder diffraction (NPD) and high-resolution transmission electron microscopy (HRTEM) reveals a complex superstructure in the ordered perovskite NaLaMgWO6. Through indexing of SAED patterns the unit-cell dimensions are found to be 46.8 × 7.8 × 7.9 Å, which corresponds to a 12ap × 2ap × 2ap superstructure of the simple Pm\overline 3 m perovskite unit cell. HRTEM images reveal the formation of an unmistakable stripe contrast that repeats with the same periodicity. Doubling of the b and c axes is brought about by a combination of layered ordering of Na and La, rock-salt ordering of Mg and W, and octahedral tilting. The a axis repeat distance results from a one-dimensional twinning of the octahedral tilts in combination with a compositional modulation. Modeling of the NPD pattern shows that the underlying tilt system is a−a−c0 with tilt angles of ∼ 8° about the a and b axes. The octahedral tilt-twin boundaries run perpendicular to the a axis and are separated by 6ap. Simulated HRTEM images show that octahedral tilt twinning alone cannot explain the stripes seen in the HRTEM images, rather a compositional modulation involving the A-site cations is necessary to explain the experimental images. text/html Octahedral tilt twinning and compositional modulation in NaLaMgWO6 text 6 65 2009-10-27 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 676 683 http://scripts.iucr.org/cgi-bin/paper?sn5089 The differences between Wang and Liebau's [Wang & Liebau (2007). Acta Cryst. B63, 216–228] stoichiometric valence (atomic valence) and structural valence (bond-valence sum) observed in Sn2+ and other lone-pair cation oxycomplexes arises from their use of the Brese & O'Keeffe bond-valence parameters which are based on the assumption that the bond-valence parameter b = 0.37 Å applies to all bond types. According to the theory of the bond-valence model, the bond-valence sum is necessarily equal to the ionic charge, implying that in the Wang and Liebau model the ionic charges are equal to the structural valence. If charges are chosen equal to the stoichiometric valence, the bond-valence parameters for Sn2+—O bonds are R0 = 1.859 Å, b = 0.55 Å. While both models are theoretically valid, only the standard model relates bond valences to the concept of atomic valence. Wang and Liebau's suggestion that cation–lone-pair bonds make a significant contribution to the valence sums is confirmed, but such bonds cannot account for the full difference between the stoichiometric and structural valences because they are present in only a few compounds. Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Brown, I.D. 2009-10-27 doi:10.1107/S0108768109034417 International Union of Crystallography A critique of Wang and Liebau's proposed concept of structural valence is presented. en oxycomplexes atomic valence bond-valence sum The differences between Wang and Liebau's [Wang & Liebau (2007). Acta Cryst. B63, 216–228] stoichiometric valence (atomic valence) and structural valence (bond-valence sum) observed in Sn2+ and other lone-pair cation oxycomplexes arises from their use of the Brese & O'Keeffe bond-valence parameters which are based on the assumption that the bond-valence parameter b = 0.37 Å applies to all bond types. According to the theory of the bond-valence model, the bond-valence sum is necessarily equal to the ionic charge, implying that in the Wang and Liebau model the ionic charges are equal to the structural valence. If charges are chosen equal to the stoichiometric valence, the bond-valence parameters for Sn2+—O bonds are R0 = 1.859 Å, b = 0.55 Å. While both models are theoretically valid, only the standard model relates bond valences to the concept of atomic valence. Wang and Liebau's suggestion that cation–lone-pair bonds make a significant contribution to the valence sums is confirmed, but such bonds cannot account for the full difference between the stoichiometric and structural valences because they are present in only a few compounds. text/html On the valences of bonds in the oxycomplexes of Sn2+ text 6 65 2009-10-27 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 684 693 http://scripts.iucr.org/cgi-bin/paper?wh5007 SrRuO3 (SRO) thin films grown on (001)p (p = pseudocubic) oriented LaAlO3 (LAO) by pulsed laser deposition have been characterized using transmission electron microscopy. Observations along the 〈100〉p directions suggests that although the SRO layer maintains a pseudocube-to-pseudocube orientation relationship with the underlying LAO substrate, it has a ferroelastic domain structure associated with a transformation on cooling to room temperature to an orthorhombic Pbnm phase (a−a−c+ Glazer tilt system). In addition, extra diffraction spots located at ±1/6(ooo)p and ±1/3(ooo)p (where `o' indicates an index with an odd number) positions were obtained in 〈110〉p zone-axis diffraction patterns. These were attributed to the existence of high-density twins on {111}p pseudocubic planes within the SrRuO3 films rather than to more conventional mechanisms for the generation of superstructure reflections. Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Han, Y. Reaney, I.M. Tinberg, D.S. Trolier-McKinstry, S. 2009-11-16 doi:10.1107/S0108768109045121 International Union of Crystallography Extra spots located at one-sixth and one-third positions on 〈110〉p (p = pseudocubic) zone-axis diffraction patterns were attributed to the existence of high-density twins on {111}p pseudocubic planes within the SrRuO3 films rather than to more conventional mechanisms for the generation of superstructure reflections. en microtwinning pulsed laser deposition transmission electron microscopy superstructure reflections SrRuO3 (SRO) thin films grown on (001)p (p = pseudocubic) oriented LaAlO3 (LAO) by pulsed laser deposition have been characterized using transmission electron microscopy. Observations along the 〈100〉p directions suggests that although the SRO layer maintains a pseudocube-to-pseudocube orientation relationship with the underlying LAO substrate, it has a ferroelastic domain structure associated with a transformation on cooling to room temperature to an orthorhombic Pbnm phase (a−a−c+ Glazer tilt system). In addition, extra diffraction spots located at ±1/6(ooo)p and ±1/3(ooo)p (where `o' indicates an index with an odd number) positions were obtained in 〈110〉p zone-axis diffraction patterns. These were attributed to the existence of high-density twins on {111}p pseudocubic planes within the SrRuO3 films rather than to more conventional mechanisms for the generation of superstructure reflections. text/html (111)p microtwinning in SrRuO3 thin films on (001)p LaAlO3 text 6 65 2009-11-16 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 694 698 http://scripts.iucr.org/cgi-bin/paper?ps5003 Reaction of silver(I) salts with three equivalents of tri-p-tolylphosphine in CH3CN resulted in a series of isomorphous complexes [AgX{P(4-MeC6H4)3}3] (X = Br, SCN, ClO4). These complexes all crystallize in the orthorhombic space group Pna21. The complexes with X = Br, SCN are distorted tetrahedral around the silver(I) atom, whereas the ClO4− complex is distorted trigonal planar around the silver. The new complexes are compared with each other using r.m.s. overlay calculations as well as half-normal probability plot analysis and with the previously reported isomorphous chloride, bromide as well as the non-isomorphous iodide complexes. Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Omondi, B. Venter, G.J.S. Roodt, A. Meijboom, R. 2009-11-16 doi:10.1107/S0108768109036404 International Union of Crystallography The synthesis and characterization of isomorphous silver(I) complexes [AgX{P(4-MeC6H4)3}3] (X = Br, SCN, ClO4) using single-crystal X-ray diffraction are described and compared with related structures from the literature. The molecular structures of the three complexes are compared using an r.m.s. overlay as well as a half-normal probability plot analysis. en silver isomorphism phosphine half-normal probability Reaction of silver(I) salts with three equivalents of tri-p-tolylphosphine in CH3CN resulted in a series of isomorphous complexes [AgX{P(4-MeC6H4)3}3] (X = Br, SCN, ClO4). These complexes all crystallize in the orthorhombic space group Pna21. The complexes with X = Br, SCN are distorted tetrahedral around the silver(I) atom, whereas the ClO4− complex is distorted trigonal planar around the silver. The new complexes are compared with each other using r.m.s. overlay calculations as well as half-normal probability plot analysis and with the previously reported isomorphous chloride, bromide as well as the non-isomorphous iodide complexes. text/html Isomorphism in monomeric 1:3 complexes of silver(I) salts with tri-p-tolylphosphine text 6 65 2009-11-16 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 699 706 http://scripts.iucr.org/cgi-bin/paper?gp5034 The dSNAP computer program has been used to classify searches of the Cambridge Structural Database for two ligands: —O—CH2—CH2—O— and N(CH2CH2O—)3 commonly found in metal-organic systems. The clustering method used is based on total geometries (i.e. all the lengths and angles involving all the atoms in the search fragment, whether bonded or not) and proved capable of distinguishing in a wholly automatic, objective way between different types of metal complex purely on the basis of the geometry of the ligand and the relative positions of the O atoms to the metals. Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Collins, A. Wilson, C.C. Gilmore, C.J. 2009-11-16 doi:10.1107/S0108768109038051 International Union of Crystallography The dSNAP computer program has been used to classify searches of the Cambridge Structural Database for two ligands commonly found in metal-organic systems. en cluster analysis dSNAP software Cambridge Structural Database The dSNAP computer program has been used to classify searches of the Cambridge Structural Database for two ligands: —O—CH2—CH2—O— and N(CH2CH2O—)3 commonly found in metal-organic systems. The clustering method used is based on total geometries (i.e. all the lengths and angles involving all the atoms in the search fragment, whether bonded or not) and proved capable of distinguishing in a wholly automatic, objective way between different types of metal complex purely on the basis of the geometry of the ligand and the relative positions of the O atoms to the metals. text/html Cluster analyses of metal-organic fragments using the dSNAP software text 6 65 2009-11-16 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 707 714 http://scripts.iucr.org/cgi-bin/paper?pi5003 Details of the complex bonding environment present in the molecular centre of an alkyne-bridged dicobalt complex have been examined using a combination of experimental and theoretical charge-density modelling for two compounds which share a central Co2C2 tetrahedral moiety as their common motif. Topological analysis of the experimental electron density illustrates the problem of separating the Co—C bond-critical points (b.c.p.s) from the intervening ring-critical point (r.c.p.), due largely to the flat nature of the electron density in the CoC2 triangles. Such a separation of critical points is immediately obtained from a topological analysis of the theoretical electron density as well as from the multipole-projected theoretical density; however, the addition of random noise to the theoretical structure factors prior to multipole modelling leads to a failure in consistently distinguishing two b.c.p.s and one r.c.p. in such close proximity within the particular environment of this Co2C2 centre. Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Overgaard, J. Platts, J.A. Iversen, B.B. 2009-11-16 doi:10.1107/S0108768109045091 International Union of Crystallography Random noise added to theoretical structure factors for a cobalt carbonyl complex is shown to have a large influence on the resulting topological landscape with the potential disappearance of bond-critical points. Atoms in molecules (AIM) analysis of the experimental charge density shows evidence of all the bond-critical points while being highly sensitive to the chosen parameter set. en single-crystal X-ray diffraction charge-density distribution topological analysis theoretical structure factors Details of the complex bonding environment present in the molecular centre of an alkyne-bridged dicobalt complex have been examined using a combination of experimental and theoretical charge-density modelling for two compounds which share a central Co2C2 tetrahedral moiety as their common motif. Topological analysis of the experimental electron density illustrates the problem of separating the Co—C bond-critical points (b.c.p.s) from the intervening ring-critical point (r.c.p.), due largely to the flat nature of the electron density in the CoC2 triangles. Such a separation of critical points is immediately obtained from a topological analysis of the theoretical electron density as well as from the multipole-projected theoretical density; however, the addition of random noise to the theoretical structure factors prior to multipole modelling leads to a failure in consistently distinguishing two b.c.p.s and one r.c.p. in such close proximity within the particular environment of this Co2C2 centre. text/html Experimental and theoretical charge-density study of a tetranuclear cobalt carbonyl complex text 6 65 2009-11-16 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 715 723 http://scripts.iucr.org/cgi-bin/paper?kd5033 The (S)-4-alkoxo-2-azetidinecarboxylic acids are optically active β-lactam derivatives of aspartic acid, which are used as precursors of carbapenem-type antibiotics and poly-β-aspartates. The crystal structures of three (S)-4-alkoxo-2-azetidinecarboxylic acids with alkyl chains with 10, 12 and 16 C atoms were solved using parallel tempering and refined against the X-ray powder diffraction data using the Rietveld method. The azetidinone rings in the three compounds display a pattern of asymmetrical bond distances and an almost planar conformation; these characteristics are compared with periodic solid-state, gas-phase density-functional theory (DFT) calculations and MOGUL average bond distances and angles from the CSD. The compounds pack along [001] as corrugated sheets separated by approximately 4.40 Å and connected by hydrogen bonds of the type N—H...O. Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Seijas, L.E. Mora, A.J. Delgado, G.E. López-Carrasquero, F. Báez, M.E. Brunelli, M. Fitch, A.N. 2009-11-16 doi:10.1107/S0108768109036386 International Union of Crystallography The crystal structures of three (S)-4-alkoxo-2-azetidinecarboxylic acids (with alkoxo = decyloxo, dodecyloxo and hexadecyloxo) were solved and refined from synchrotron X-ray powder diffraction data and compared with density-functional theory calculations. en powder diffraction structure solution β-lactams hydrogen bonds The (S)-4-alkoxo-2-azetidinecarboxylic acids are optically active β-lactam derivatives of aspartic acid, which are used as precursors of carbapenem-type antibiotics and poly-β-aspartates. The crystal structures of three (S)-4-alkoxo-2-azetidinecarboxylic acids with alkyl chains with 10, 12 and 16 C atoms were solved using parallel tempering and refined against the X-ray powder diffraction data using the Rietveld method. The azetidinone rings in the three compounds display a pattern of asymmetrical bond distances and an almost planar conformation; these characteristics are compared with periodic solid-state, gas-phase density-functional theory (DFT) calculations and MOGUL average bond distances and angles from the CSD. The compounds pack along [001] as corrugated sheets separated by approximately 4.40 Å and connected by hydrogen bonds of the type N—H...O. text/html Molecular and crystalline structures of three (S)-4-alkoxycarbonyl-2-azetidinones containing long alkyl side chains from synchrotron X-ray powder diffraction data text 6 65 2009-11-16 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 724 730 http://scripts.iucr.org/cgi-bin/paper?ws5073 We report the effect of pressure on the crystal structures of betaine monohydrate (BTM), l-cysteic acid monohydrate (CAM) and S-4-sulfo-l-phenylalanine monohydrate (SPM). All three structures are composed of layers of zwitterionic molecules separated by layers of water molecules. In BTM the water molecules make donor interactions with the same layer of betaine molecules, and the structure remains in a compressed form of its ambient-pressure phase up to 7.8 GPa. CAM contains bi-layers of l-cysteic acid molecules separated by water molecules which form donor interactions to the bi-layers above and below. This phase is stable up to 6.8 GPa. SPM also contains layers of zwitterionic molecules with the waters acting as hydrogen-bond donors to the layers above and below. SPM undergoes a single-crystal to single-crystal phase transition above 1 GPa in which half the water molecules reorient so as to form one donor interaction with another water molecule within the same layer. In addition, half of the S-4-sulfo-l-phenylalanine molecules change their conformation. The high-pressure phase is stable up to 6.9 GPa, although modest rearrangements in hydrogen bonding and molecular conformation occur at 6.4 GPa. The three hydrates had been selected on the basis of their topological similarity (CAM and SPM) or dissimilarity (BTM) with serine hydrate, which undergoes a phase transition at 5 GPa in which the water molecules change orientation. The phase transition in SPM shows some common features with that in serine hydrate. The principal directions of compression in all three structures were found to correlate with directions of hydrogen bonds and distributions of interstitial voids. Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Johnstone, R.D.L. Lennie, A.R. Parsons, S. Pidcock, E. Warren, J.E. 2009-11-16 doi:10.1107/S0108768109039469 International Union of Crystallography Although the monohydrates of betaine, cysteic acid and S-4-sulfo-l-phenylalanine all contain hydrate layers, they differ in the orientations of the water molecules. The topologies of S-4-sulfo-l-phenylalanine and betaine monohydrates led us to predict that the former would undergo a phase transition at high pressure, while the latter would not. en layered hydrates high-pressure polymorphism phase transitions zwitterions We report the effect of pressure on the crystal structures of betaine monohydrate (BTM), l-cysteic acid monohydrate (CAM) and S-4-sulfo-l-phenylalanine monohydrate (SPM). All three structures are composed of layers of zwitterionic molecules separated by layers of water molecules. In BTM the water molecules make donor interactions with the same layer of betaine molecules, and the structure remains in a compressed form of its ambient-pressure phase up to 7.8 GPa. CAM contains bi-layers of l-cysteic acid molecules separated by water molecules which form donor interactions to the bi-layers above and below. This phase is stable up to 6.8 GPa. SPM also contains layers of zwitterionic molecules with the waters acting as hydrogen-bond donors to the layers above and below. SPM undergoes a single-crystal to single-crystal phase transition above 1 GPa in which half the water molecules reorient so as to form one donor interaction with another water molecule within the same layer. In addition, half of the S-4-sulfo-l-phenylalanine molecules change their conformation. The high-pressure phase is stable up to 6.9 GPa, although modest rearrangements in hydrogen bonding and molecular conformation occur at 6.4 GPa. The three hydrates had been selected on the basis of their topological similarity (CAM and SPM) or dissimilarity (BTM) with serine hydrate, which undergoes a phase transition at 5 GPa in which the water molecules change orientation. The phase transition in SPM shows some common features with that in serine hydrate. The principal directions of compression in all three structures were found to correlate with directions of hydrogen bonds and distributions of interstitial voids. text/html Comparison of the effects of pressure on three layered hydrates: a partially successful attempt to predict a high-pressure phase transition text 6 65 2009-11-16 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 731 748 http://scripts.iucr.org/cgi-bin/paper?sn5088 Bergenin, which has been isolated from a variety of tropical plants, has several pharmacological applications in traditional Asian medicine. Its electron-density distribution was obtained from a room-temperature low-resolution X-ray data set measured with point detection making use of multipole populations from the invariom library. Two refinement models were considered. In a first step, positional parameters and ADPs were refined with fixed library multipoles (model E1). This model was suitable to be input into a second refinement of multipoles (model E2), which converged smoothly although based on Cu Kα room-temperature data. Quantitative results of a topological analysis of the electron density from both models were compared with Hartree–Fock and density-functional calculations. With respect to the independent atom model (IAM) more information can be extracted from invariom modelling, including the electrostatic potential and hydrogen-bond energies, which are highly useful, especially for biologically active compounds. The reliability of the applied invariom formalism was assessed by a comparison of bond-topological properties of sucrose, for which high-resolution multipole and invariom densities were available. Since a conventional X-ray diffraction experiment using basic equipment was combined with the easy-to-use invariom formalism, the procedure described here for bergenin illustrates how it can be routinely applied in pharmacological research. Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Dittrich, B. Weber, M. Kalinowski, R. Grabowsky, S. Hübschle, C.B. Luger, P. 2009-11-16 doi:10.1107/S0108768109046060 International Union of Crystallography The detailed electron-density distribution of bergenin, an anti-HIV agent, has been determined. It is shown that even a low-order data set measured at room temperature with Ni-filtered Cu Kα radiation and point detection can provide information far beyond the outcomes of an independent atom model refinement. en bergenin refinement models density-functional calculations Hartree–Fock calculations independent atom model Bergenin, which has been isolated from a variety of tropical plants, has several pharmacological applications in traditional Asian medicine. Its electron-density distribution was obtained from a room-temperature low-resolution X-ray data set measured with point detection making use of multipole populations from the invariom library. Two refinement models were considered. In a first step, positional parameters and ADPs were refined with fixed library multipoles (model E1). This model was suitable to be input into a second refinement of multipoles (model E2), which converged smoothly although based on Cu Kα room-temperature data. Quantitative results of a topological analysis of the electron density from both models were compared with Hartree–Fock and density-functional calculations. With respect to the independent atom model (IAM) more information can be extracted from invariom modelling, including the electrostatic potential and hydrogen-bond energies, which are highly useful, especially for biologically active compounds. The reliability of the applied invariom formalism was assessed by a comparison of bond-topological properties of sucrose, for which high-resolution multipole and invariom densities were available. Since a conventional X-ray diffraction experiment using basic equipment was combined with the easy-to-use invariom formalism, the procedure described here for bergenin illustrates how it can be routinely applied in pharmacological research. text/html How to easily replace the independent atom model – the example of bergenin, a potential anti-HIV agent of traditional Asian medicine text 6 65 2009-11-16 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 749 756 http://scripts.iucr.org/cgi-bin/paper?pi5002 The charge density in (±)-8′-benzhydrylideneamino-1,1′-binaphthyl-2-ol (1) has been studied experimentally using Mo Kα X-ray diffraction at 100 K, and by theory using density-functional thoery (DFT) calculations at the B3LYP/6-311++G** level. The nature of the weak intramolecular peri-C...N, CH...π, H...H and C(π)...C(π) interactions has been examined by topological analysis using the Quantum Theory of Atoms in Molecules (QTAIM) approach. An analysis of the density ρ(r), the Laplacian of the density ∇2ρ(rb) and other topological properties at the bond-critical points were used to classify these interactions. The study confirms the presence of the intramolecular CH...π interaction in (1), which was previously suspected on geometrical grounds. An analysis of the ellipticity profiles along the bond paths unambiguously shows the π-delocalization between the imine unit and one N-phenyl group. The weak intermolecular interactions in the crystal of (1) were examined experimentally and theoretically through the pairwise interactions of the seven independent dimeric pairs of (1) responsible for the set of unique intermolecular interactions, and also through examination of the Hirshfeld surface dnorm property. The theoretical dimeric-pair calculations used the BLYP-D functional which supplements the exchange-correlational functional with an empirical dispersion term to provide a more accurate determination of the energies for the weak intermolecular interactions. Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Farrugia, L.J. Kočovský, P. Senn, H.M. Vyskočil, Š. 2009-10-27 doi:10.1107/S010876810903273X International Union of Crystallography An Atoms in Molecules (AIM) analysis of the experimental and theoretical charge density in the title compound confirms the presence of an intramolecular CH...π interaction, which was originally suspected on geometrical grounds. The other weak intra- and intermolecular interactions and π-delocalization effects were examined by AIM topological analysis and ellipticity profiles. en charge-density study density-functional theory topological properties bond-critical points inter- and intramolecular interactions The charge density in (±)-8′-benzhydrylideneamino-1,1′-binaphthyl-2-ol (1) has been studied experimentally using Mo Kα X-ray diffraction at 100 K, and by theory using density-functional thoery (DFT) calculations at the B3LYP/6-311++G** level. The nature of the weak intramolecular peri-C...N, CH...π, H...H and C(π)...C(π) interactions has been examined by topological analysis using the Quantum Theory of Atoms in Molecules (QTAIM) approach. An analysis of the density ρ(r), the Laplacian of the density ∇2ρ(rb) and other topological properties at the bond-critical points were used to classify these interactions. The study confirms the presence of the intramolecular CH...π interaction in (1), which was previously suspected on geometrical grounds. An analysis of the ellipticity profiles along the bond paths unambiguously shows the π-delocalization between the imine unit and one N-phenyl group. The weak intermolecular interactions in the crystal of (1) were examined experimentally and theoretically through the pairwise interactions of the seven independent dimeric pairs of (1) responsible for the set of unique intermolecular interactions, and also through examination of the Hirshfeld surface dnorm property. The theoretical dimeric-pair calculations used the BLYP-D functional which supplements the exchange-correlational functional with an empirical dispersion term to provide a more accurate determination of the energies for the weak intermolecular interactions. text/html Weak intra- and intermolecular interactions in a binaphthol imine: an experimental charge-density study on (±)-8′-benzhydrylideneamino-1,1′-binaphthyl-2-ol text 6 65 2009-10-27 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 757 769 http://scripts.iucr.org/cgi-bin/paper?gp5033 Structural changes in the high-temperature ∊-polymorph of chlorpropamide, 4-chloro-N-(propylaminocarbonyl)benzenesulfonamide, C10H13ClN2O3S, on cooling down to 100 K and on reverse heating were followed by single-crystal X-ray diffraction. At temperatures below 200 K the phase transition into a new polymorph (termed the ∊′-form) has been observed for the first time. The polymorphic transition preserves the space group Pna21, is reversible and is accompanied by discontinuous changes in the cell volume and parameters, resulting from changes in molecular conformation. As shown by IR spectroscopy and X-ray powder diffraction, the phase transition in a powder sample is inhomogeneous throughout the bulk, and the two phases co-exist in a wide temperature range. The cell parameters and the molecular conformation in the new polymorph are close to those in the previously known α-polymorph, but the packing of the z-shaped molecular ribbons linked by hydrogen bonds inherits that of the ∊-form and is different from the packing in the α-polymorph. A structural study of the α-polymorph in the same temperature range has revealed no phase transitions. Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Drebushchak, T.N. Chesalov, Y.A. Boldyreva, E.V. 2009-10-27 doi:10.1107/S010876810903290X International Union of Crystallography A reversible phase transition into a new polymorph of chlorpropamide on cooling the ∊-form below 200 K has been observed for the first time and followed by single-crystal and powder X-ray diffraction and IR spectroscopy. en polymorphism chlorpropamide molecular conformation hydrogen bonds Structural changes in the high-temperature ∊-polymorph of chlorpropamide, 4-chloro-N-(propylaminocarbonyl)benzenesulfonamide, C10H13ClN2O3S, on cooling down to 100 K and on reverse heating were followed by single-crystal X-ray diffraction. At temperatures below 200 K the phase transition into a new polymorph (termed the ∊′-form) has been observed for the first time. The polymorphic transition preserves the space group Pna21, is reversible and is accompanied by discontinuous changes in the cell volume and parameters, resulting from changes in molecular conformation. As shown by IR spectroscopy and X-ray powder diffraction, the phase transition in a powder sample is inhomogeneous throughout the bulk, and the two phases co-exist in a wide temperature range. The cell parameters and the molecular conformation in the new polymorph are close to those in the previously known α-polymorph, but the packing of the z-shaped molecular ribbons linked by hydrogen bonds inherits that of the ∊-form and is different from the packing in the α-polymorph. A structural study of the α-polymorph in the same temperature range has revealed no phase transitions. text/html A conformational polymorphic transition in the high-temperature ∊-form of chlorpropamide on cooling: a new ∊′-form text 6 65 2009-10-27 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 770 781 http://scripts.iucr.org/cgi-bin/paper?bk5088 A survey of recent entries in the Cambridge Structural Database suggests that the percentage of structures described in space groups of inappropriately low symmetry has decreased from about 10% in the early 2000s to less than 5% today for space group Cc, but that for space group P1 it remains close to 8%. Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Marsh, R.E. 2009-11-16 doi:10.1107/S0108768109046448 International Union of Crystallography A survey of recent entries in the Cambridge Structural Database suggests that the percentage of structures described in space groups of inappropriately low symmetry has decreased from about 10% in the early 2000s to less than 5% today for space group Cc, but that for space group P1 it remains close to 8%. en space groups Cambridge Structural Database low symmetry A survey of recent entries in the Cambridge Structural Database suggests that the percentage of structures described in space groups of inappropriately low symmetry has decreased from about 10% in the early 2000s to less than 5% today for space group Cc, but that for space group P1 it remains close to 8%. text/html Space groups P1 and Cc: how are they doing? text 6 65 2009-11-16 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science short communications 782 783 http://scripts.iucr.org/cgi-bin/paper?bk5090 The low-temperature structure of 4-methylpyridine-N-oxide was previously determined in symmetry P41 [Damay et al. (2006), Acta Cryst. B62, 627–633]. Using a recently published symmetry-determination method it was found that the true symmetry of the structure is P41212. The structure was refined in the new space group using X-ray and neutron data. The previously published structure is close to the newly refined structure, but the new structure is in agreement with the results of rotational tunneling spectroscopy, and, in contrast to the structure in symmetry P41, does not require a twofold degeneracy of the tunneling bands. Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Palatinus, L. Damay, F. 2009-11-16 doi:10.1107/S0108768109042608 International Union of Crystallography A low-temperature structure of the title compound was redetermined in the correct space group. The symmetry was determined ab initio by a recently published symmetry-determination algorithm. en symmetry determination charge flipping powder diffraction The low-temperature structure of 4-methylpyridine-N-oxide was previously determined in symmetry P41 [Damay et al. (2006), Acta Cryst. B62, 627–633]. Using a recently published symmetry-determination method it was found that the true symmetry of the structure is P41212. The structure was refined in the new space group using X-ray and neutron data. The previously published structure is close to the newly refined structure, but the new structure is in agreement with the results of rotational tunneling spectroscopy, and, in contrast to the structure in symmetry P41, does not require a twofold degeneracy of the tunneling bands. text/html Towards a more reliable symmetry determination from powder diffraction: a redetermination of the low-temperature structure of 4-methylpyridine-N-oxide text 6 65 2009-11-16 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science short communications 784 786 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. 2009-11-16 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 6 65 2009-11-16 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science addenda and errata 787 787 http://scripts.iucr.org/cgi-bin/paper?es0375 Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7681 Abrahams, S.C. Hedberg, K. 2009-11-16 doi:10.1107/S0108768109047533 International Union of Crystallography en Obituaries text/html Clara Brink Shoemaker (1921–2009) text 6 65 2009-11-16 Copyright (c) 2009 International Union of Crystallography Acta Crystallographica Section B: Structural Science obituaries 788 790