http://journals.iucr.org/b/issues/2008/01/00/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) 2008 International Union of Crystallography 2008-02-01 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 64, Part 1, 2008 text yearly 6 2002-02-01T00:00+00:00 1 64 2008-02-01 Copyright (c) 2008 International Union of Crystallography Acta Crystallographica Section B: Structural Science 1 urn:issn:0108-7681 med@iucr.org February 2008 2008-02-01 http://journals.iucr.org/logos/rss10b.gif http://journals.iucr.org/b/issues/2008/01/00/isscontsbdy.html Still image http://scripts.iucr.org/cgi-bin/paper?ck5029 A temperature-dependent structural investigation of the substituted argyrodite Ag7GeSe5I has been carried out on a single crystal from 15 to 475 K, in steps of 50 K, and correlated to its conductivity properties. The argyrodite crystallizes in a cubic cell with the F\bar 43m space group. The crystal structure exhibits high static and dynamic disorder which has been efficiently accounted for using a combination of (i) Gram–Charlier development of the Debye–Waller factors for iodine and silver, and (ii) a split-atom model for Ag+ ions. An increased delocalization of the mobile d10 Ag+ cations with temperature has been clearly shown by the inspection of the joint probability-density functions; the corresponding diffusion pathways have been determined. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7681 Albert, S. Pillet, S. Lecomte, C. Pradel, A. Ribes, M. 2008-01-17 doi:10.1107/S0108768107059642 International Union of Crystallography A temperature-dependent structural investigation of the substituted argyrodite Ag7GeSe5I has been carried out on a single crystal from 15 K up to 475 K in steps of 50 K. The results of that study have been correlated with the crystal's conductivity properties. en argyrodite superionic conductor disorder anharmonicity silver-ion distribution A temperature-dependent structural investigation of the substituted argyrodite Ag7GeSe5I has been carried out on a single crystal from 15 to 475 K, in steps of 50 K, and correlated to its conductivity properties. The argyrodite crystallizes in a cubic cell with the F\bar 43m space group. The crystal structure exhibits high static and dynamic disorder which has been efficiently accounted for using a combination of (i) Gram–Charlier development of the Debye–Waller factors for iodine and silver, and (ii) a split-atom model for Ag+ ions. An increased delocalization of the mobile d10 Ag+ cations with temperature has been clearly shown by the inspection of the joint probability-density functions; the corresponding diffusion pathways have been determined. text/html Disorder in Ag7GeSe5I, a superionic conductor: temperature-dependent anharmonic structural study text 1 64 2008-01-17 Copyright (c) 2008 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 1 11 http://scripts.iucr.org/cgi-bin/paper?bp5005 The previously reported incommensurately modulated scheelite-like structure KNd(MoO4)2 has been exploited as a natural (3 + 1)-dimensional superspace model to generate the scheelite-like three-dimensional structure family. Although each member differs in its space-group symmetry, unit-cell parameters and compositions, in (3 + 1)-dimensional space, they share a common superspace group, a common number of building units in the basic unit cell occupying Wyckoff sites with specific coordinates (x, y, z) and specific basic unit-cell axial ratios (c/a, a/b, b/c) and angles. Variations of the modulation vector q, occupation functions and t0 are exploited for the derivation. Eight topologically and compositionally different known structures are compared with their models derived from the KNd(MoO4)2 structure in order to evaluate the capabilities and limitations of the incommensurately modulated structure to act as a superspace generating model. Applications of the KNd(MoO4)2 structure as a starting model for the refinement and prediction of some other modulated members of the family is also illustrated. The (3 + 1)-dimensional presentation of the scheelite-like structures reveals new structural relations, which remain hidden if only conventional three-dimensional structure descriptions are applied. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7681 Arakcheeva, A. Chapuis, G. 2008-01-17 doi:10.1107/S010876810705923X International Union of Crystallography A (3 + d)-dimensional incommensurately modulated structure can be exploited as a natural superspace model for the generation, prediction and description of a (3 + d)-dimensional family consisting of both three-dimensional and (3 + d)-dimensional members. The capabilities and limitations of an incommensurately modulated structure to act as a natural superspace model for the generation of a family are illustrated with an example of the scheelite-like compound derived from the (3 + 1)-dimensional incommensurately modulated KNd(MoO4)2 structure. en superspace model incommensurately modulated structure occupation modulations scheelite-like structures composition ordering The previously reported incommensurately modulated scheelite-like structure KNd(MoO4)2 has been exploited as a natural (3 + 1)-dimensional superspace model to generate the scheelite-like three-dimensional structure family. Although each member differs in its space-group symmetry, unit-cell parameters and compositions, in (3 + 1)-dimensional space, they share a common superspace group, a common number of building units in the basic unit cell occupying Wyckoff sites with specific coordinates (x, y, z) and specific basic unit-cell axial ratios (c/a, a/b, b/c) and angles. Variations of the modulation vector q, occupation functions and t0 are exploited for the derivation. Eight topologically and compositionally different known structures are compared with their models derived from the KNd(MoO4)2 structure in order to evaluate the capabilities and limitations of the incommensurately modulated structure to act as a superspace generating model. Applications of the KNd(MoO4)2 structure as a starting model for the refinement and prediction of some other modulated members of the family is also illustrated. The (3 + 1)-dimensional presentation of the scheelite-like structures reveals new structural relations, which remain hidden if only conventional three-dimensional structure descriptions are applied. text/html Capabilities and limitations of a (3 + d)-dimensional incommensurately modulated structure as a model for the derivation of an extended family of compounds: example of the scheelite-like structures text 1 64 2008-01-17 Copyright (c) 2008 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 12 25 http://scripts.iucr.org/cgi-bin/paper?av5093 Tessellations by generating clusters are proposed for the high-pressure phases BC8 and R8 of silicon. The structures of both high-pressure phases are represented by the parallel packings of rods. The latter are stacks of distorted icosahedra, joined by a common triangular face and flattened out along the threefold symmetry axis. Along the rod axis there is an alternation of empty and double-centered icosahedra. The empty icosahedra are additionally distorted in the cubic BC8 phase by antiparallel rotation about the rod axis, while the double-centered icosahedra are distorted by that rotation in the rhombohedral R8 phase. A possible mechanism of the reversible BC8 ↔ R8 transformation is proposed as the rotation about the rod axis of the common triangular face of the neighboring icosahedra, thus transforming between distorted and undistorted icosahedra. The graphs of the generating clusters for both the BC8 and R8 structures are determined by two subconfigurations of the same construction of the finite projective geometry. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7681 Kraposhin, V.S. Talis, A.L. Kosushkin, V.G. Ogneva, A.A. Zinober, L.I. 2008-01-17 doi:10.1107/S0108768107059800 International Union of Crystallography Structures of the high-pressure phases BC8 and R8 of silicon are described as parallel rod packings, where rods are stacks of flattened icosahedra. The mechanism of the transformation between these modifications is described as the rotation of a common triangular face between two neighboring icosahedra. en high-pressure phase phase transition algebraic geometry Tessellations by generating clusters are proposed for the high-pressure phases BC8 and R8 of silicon. The structures of both high-pressure phases are represented by the parallel packings of rods. The latter are stacks of distorted icosahedra, joined by a common triangular face and flattened out along the threefold symmetry axis. Along the rod axis there is an alternation of empty and double-centered icosahedra. The empty icosahedra are additionally distorted in the cubic BC8 phase by antiparallel rotation about the rod axis, while the double-centered icosahedra are distorted by that rotation in the rhombohedral R8 phase. A possible mechanism of the reversible BC8 ↔ R8 transformation is proposed as the rotation about the rod axis of the common triangular face of the neighboring icosahedra, thus transforming between distorted and undistorted icosahedra. The graphs of the generating clusters for both the BC8 and R8 structures are determined by two subconfigurations of the same construction of the finite projective geometry. text/html Structures of the cubic and rhombohedral high-pressure modifications of silicon as packing of the rod-like substructures determined by the algebraic geometry text 1 64 2008-01-17 Copyright (c) 2008 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 26 33 http://scripts.iucr.org/cgi-bin/paper?lm5013 The crystal chemistries of synthetic mimetite, Pb10(As5+O4)6(Cl2 − xOx/2), a neutral apatite, and finnemanite, Pb10(As3+O3)6Cl2, a reduced apatite, were characterized using a combination of X-ray powder diffraction, neutron diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Both phases conform to hexagonal P63/m symmetry; however, the temperature-driven transformation of clinomimetite to mimetite described earlier was not confirmed. The average mimetite structure is best described through the introduction of partially occupied oxygen sites. A better understanding of the mixed arsenic speciation in apatites can guide the formulation of waste form ceramics and improve models of long-term durability after landfill disposal. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7681 Baikie, T. Ferraris, C. Klooster, W.T. Madhavi, S. Pramana, S.S. Pring, A. Schmidt, G. White, T.J. 2008-01-17 doi:10.1107/S0108768107066402 International Union of Crystallography Synthetic samples of the neutral apatite mimetite, Pb10(AsO4)6(Cl2 − xOx/2), and its reduced form finnemanite, Pb10(AsO3)6Cl2, have been structurally characterized using a combination of neutron diffraction, transmission electron microscopy and X-ray diffraction spectroscopy. Both materials conform to hexagonal P63/m symmetry; however, the average mimetite structure is best described through the introduction of partially occupied oxygen sites. en powder diffraction transmission electron microscropy photoelectron spectroscopy ceramics The crystal chemistries of synthetic mimetite, Pb10(As5+O4)6(Cl2 − xOx/2), a neutral apatite, and finnemanite, Pb10(As3+O3)6Cl2, a reduced apatite, were characterized using a combination of X-ray powder diffraction, neutron diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Both phases conform to hexagonal P63/m symmetry; however, the temperature-driven transformation of clinomimetite to mimetite described earlier was not confirmed. The average mimetite structure is best described through the introduction of partially occupied oxygen sites. A better understanding of the mixed arsenic speciation in apatites can guide the formulation of waste form ceramics and improve models of long-term durability after landfill disposal. text/html Crystal chemistry of mimetite, Pb10(AsO4)6Cl1.48O0.26, and finnemanite, Pb10(AsO3)6Cl2 text 1 64 2008-01-17 Copyright (c) 2008 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 34 41 http://scripts.iucr.org/cgi-bin/paper?bs5048 Experimental electron densities and derived properties have been determined for the two energetic materials CL-20 (3,5,9,11-tetraacetyl-14-oxo-1,3,5,7,9,11-hexaazapentacyclo-[5.5.3.02,6.04,10.08,12]pentadecane), and FOX-7 (1,1-diamino-2,2-dinitroethylene) from single-crystal diffraction. Synchrotron data extending to high scattering angles were measured at low temperature. Low figures-of-merit and excellent residuals were obtained. The Hansen & Coppens multipole-model electron density was compared with results from theoretical calculations via structure factors simulating an experiment. Chemical bonding in the molecules is discussed and a topological analysis gives insight especially into the character of those bonds that are thought to play a key role in the decomposition of the molecules. A comparison of theoretical and experimental electrostatic potentials shows no obvious evidence supporting earlier findings on other nitroheterocyclic molecules that electron-density maxima near the C—NO2 bonds mapped on the electron-density isosurface can be correlated with impact sensitivities. For FOX-7 periodic Hartree–Fock calculations were performed to investigate the influence of the crystal field on the electron density distribution. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7681 Meents, A. Dittrich, B. Johnas, S.K.J. Thome, V. Weckert, E.F. 2008-01-17 doi:10.1107/S0108768107055292 International Union of Crystallography A detailed charge-density study of the two energetic materials CL-20 and FOX-7 is presented. en energetic materials topological analysis charge density Experimental electron densities and derived properties have been determined for the two energetic materials CL-20 (3,5,9,11-tetraacetyl-14-oxo-1,3,5,7,9,11-hexaazapentacyclo-[5.5.3.02,6.04,10.08,12]pentadecane), and FOX-7 (1,1-diamino-2,2-dinitroethylene) from single-crystal diffraction. Synchrotron data extending to high scattering angles were measured at low temperature. Low figures-of-merit and excellent residuals were obtained. The Hansen & Coppens multipole-model electron density was compared with results from theoretical calculations via structure factors simulating an experiment. Chemical bonding in the molecules is discussed and a topological analysis gives insight especially into the character of those bonds that are thought to play a key role in the decomposition of the molecules. A comparison of theoretical and experimental electrostatic potentials shows no obvious evidence supporting earlier findings on other nitroheterocyclic molecules that electron-density maxima near the C—NO2 bonds mapped on the electron-density isosurface can be correlated with impact sensitivities. For FOX-7 periodic Hartree–Fock calculations were performed to investigate the influence of the crystal field on the electron density distribution. text/html Charge-density studies of energetic materials: CL-20 and FOX-7 text 1 64 2008-01-17 Copyright (c) 2008 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 42 49 http://scripts.iucr.org/cgi-bin/paper?gp5018 A statistical survey was carried out to examine the connection between hydrogen-bond ring motifs (synthons) and crystallographic special symmetry positions. In the first part, the probability of common hydrogen-bond ring motifs to occupy specific crystallographic symmetry positions of inversion centers, rotation axes and mirror planes was examined. In the second part the probability of the occurrence of hydrogen-bond ring motifs was compared between crystals of chiral molecules (which cannot form inversion or mirror symmetry) to crystals of achiral molecules and racemic crystals. The results show that the crystallographic inversion center is a very significant component in the formation of hydrogen-bond ring motifs. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7681 Eppel, S. Bernstein, J. 2008-01-17 doi:10.1107/S0108768107059629 International Union of Crystallography The probabilities that hydrogen-bond ring motifs (synthons) will occupy various crystallographic special symmetry positions, as well as the effect of chirality of molecules in the crystal on the probability of formation of hydrogen-bond ring motifs, are examined. The results show that the inversion center has a significant effect on the formation of hydrogen-bond ring motifs. en synthon hydrogen bond inversion and mirror symmetry crystal engineering Cambridge Structural Database enantiomers rotation A statistical survey was carried out to examine the connection between hydrogen-bond ring motifs (synthons) and crystallographic special symmetry positions. In the first part, the probability of common hydrogen-bond ring motifs to occupy specific crystallographic symmetry positions of inversion centers, rotation axes and mirror planes was examined. In the second part the probability of the occurrence of hydrogen-bond ring motifs was compared between crystals of chiral molecules (which cannot form inversion or mirror symmetry) to crystals of achiral molecules and racemic crystals. The results show that the crystallographic inversion center is a very significant component in the formation of hydrogen-bond ring motifs. text/html Statistical survey of hydrogen-bond motifs in crystallographic special symmetry positions, and the influence of chirality of molecules in the crystal on the formation of hydrogen-bond ring motifs text 1 64 2008-01-17 Copyright (c) 2008 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 50 56 http://scripts.iucr.org/cgi-bin/paper?ry5015 Automated cluster analysis is used to examine the conformation and configuration of pyranose sugars. Previous findings on this issue are confirmed, importantly from an analysis that requires no prior knowledge of the significant factors determining the conformational classification. The findings on the conformations adopted in the crystalline solid state are found to be different to existing quantum chemical calculations performed for d-glucose in the gas phase, but consistent with empirically determined conformations in the solution state. The use of this clustering analysis in studying chirality in the determined structures is discussed, as is the ability of this type of method to examine higher dimensions within the metric multi-dimensional scaling formalism. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7681 Collins, A. Parkin, A. Barr, G. Dong, W. Gilmore, C.J. Wilson, C.C. 2008-01-17 doi:10.1107/S0108768107067341 International Union of Crystallography Cluster analysis has been applied to pyranose sugars found in the Cambridge Structural Database. en cluster analysis pyranose sugars Automated cluster analysis is used to examine the conformation and configuration of pyranose sugars. Previous findings on this issue are confirmed, importantly from an analysis that requires no prior knowledge of the significant factors determining the conformational classification. The findings on the conformations adopted in the crystalline solid state are found to be different to existing quantum chemical calculations performed for d-glucose in the gas phase, but consistent with empirically determined conformations in the solution state. The use of this clustering analysis in studying chirality in the determined structures is discussed, as is the ability of this type of method to examine higher dimensions within the metric multi-dimensional scaling formalism. text/html Configurational and conformational classification of pyranose sugars text 1 64 2008-01-17 Copyright (c) 2008 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 57 65 http://scripts.iucr.org/cgi-bin/paper?gp5019 Understanding the conformations adopted by the sulfonamide group is essential to the understanding of the way that sulfa drugs act upon the body. The relative energies of these conformations in the solid state are estimated from the Cambridge Structural Database (CSD) using cluster analysis, and are used to confirm earlier findings that many high-level ab initio calculations do not reproduce the observed solid-state structure. These conformational studies have been extended to the adjacent torsion angles, and it has been shown that the sulfonamide group significantly affects the form adopted. The relative energies of the observed forms in the solid state have been estimated using data available in the CSD. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7681 Parkin, A. Collins, A. Gilmore, C.J. Wilson, C.C. 2008-01-17 doi:10.1107/S0108768107065895 International Union of Crystallography Relative energies of conformations of acyclic sulfonamide structures in the solid state are estimated from the Cambridge Structural Database using cluster analysis, and the effect of this group on adjacent torsion angles studied. en small molecules sulfonamide conformation solid state cluster analysis Understanding the conformations adopted by the sulfonamide group is essential to the understanding of the way that sulfa drugs act upon the body. The relative energies of these conformations in the solid state are estimated from the Cambridge Structural Database (CSD) using cluster analysis, and are used to confirm earlier findings that many high-level ab initio calculations do not reproduce the observed solid-state structure. These conformational studies have been extended to the adjacent torsion angles, and it has been shown that the sulfonamide group significantly affects the form adopted. The relative energies of the observed forms in the solid state have been estimated using data available in the CSD. text/html Using small molecule crystal structure data to obtain information about sulfonamide conformation text 1 64 2008-01-17 Copyright (c) 2008 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 66 71 http://scripts.iucr.org/cgi-bin/paper?bm5050 The structures of three new 7-aryl-benzo[h]pyrazolo[3,4-b]quinolines, 8-methyl-7-(4-chlorophenyl)-10-phenyl-6,10-dihydro-5H-benzo[h]pyrazolo[3,4-b]quinoline, C27H20ClN3, 8-methyl-7-(3-pyridinyl)-10-phenyl-6,10-dihydro-5H-benzo[b]pyrazolo[3,4-b]quinoline, C26H20N4, and 8-methyl-7-(4-pyridinyl)-10-phenyl-10H-benzo[h]pyrazolo[3,4-b]quinoline, C26H18N4, which is an unexpected oxidation product isolated from the attempted synthesis of 8-methyl-7-(4-pyridinyl)-10-phenyl-6,10-dihydro-5H-benzo[h]pyrazolo[3,4-b]quinoline, and those of three new 11-aryl-benzo[f]pyrazolo[3,4-b]quinolines, 11-(4-methylphenyl)-10-methyl-8-phenyl-6,8-dihydro-5H-benzo[f]pyrazolo[3,4-b]quinoline, C28H23N3 (P\bar 1, Z′ = 2), 11-(4-methoxyphenyl)-10-methyl-8-phenyl-6,8-dihydro-5H-benzo[f]pyrazolo[3,4-b]quinoline, C28H23N3O (P21/c, Z′ = 4), and 11-(3,4,5-trimethoxyphenyl)-10-methyl-8-phenyl-6,8-dihydro-5H-benzo[f]pyrazolo[3,4-b]quinoline, C30H27N3O3, are reported. The crystal structures are compared with those of a number of analogues reported in the recent literature; in particular, structural comparisons are drawn within each series as the substituted pendent aryl group is varied, and between several pairs of strictly isomeric 7-aryl-benzo[h]pyrazolo[3,4-b]quinolines and 11-aryl-benzo[f]pyrazolo[3,4-b]quinolines containing the same aryl substituents within each pair. Intermolecular interactions of the C—H...π type are found in the crystal structures of both series, but π...π stacking interactions are found only in the 7-aryl-benzo[h]pyrazolo[3,4-b]quinoline series. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7681 Portilla, J. Quiroga, J. Nogueras, M. de la Torre, J.M. Cobo, J. Low, J.N. Glidewell, C. 2008-01-17 doi:10.1107/S0108768107065743 International Union of Crystallography Six new structures of benzopyrazolo[3,4-b]quinolines are reported, and structural comparisons are made both within the two series, of 7-aryl-benzo[h]pyrazolo[3,4-b]quinolines and 11-aryl-benzo[f]pyrazolo[3,4-b]quinolines, respectively, now numbering 14 structures in total, and between isomeric pairs of compounds from these two series. en structural comparisons anti-viral and anti-malarial agents cyclocondensation reactions The structures of three new 7-aryl-benzo[h]pyrazolo[3,4-b]quinolines, 8-methyl-7-(4-chlorophenyl)-10-phenyl-6,10-dihydro-5H-benzo[h]pyrazolo[3,4-b]quinoline, C27H20ClN3, 8-methyl-7-(3-pyridinyl)-10-phenyl-6,10-dihydro-5H-benzo[b]pyrazolo[3,4-b]quinoline, C26H20N4, and 8-methyl-7-(4-pyridinyl)-10-phenyl-10H-benzo[h]pyrazolo[3,4-b]quinoline, C26H18N4, which is an unexpected oxidation product isolated from the attempted synthesis of 8-methyl-7-(4-pyridinyl)-10-phenyl-6,10-dihydro-5H-benzo[h]pyrazolo[3,4-b]quinoline, and those of three new 11-aryl-benzo[f]pyrazolo[3,4-b]quinolines, 11-(4-methylphenyl)-10-methyl-8-phenyl-6,8-dihydro-5H-benzo[f]pyrazolo[3,4-b]quinoline, C28H23N3 (P\bar 1, Z′ = 2), 11-(4-methoxyphenyl)-10-methyl-8-phenyl-6,8-dihydro-5H-benzo[f]pyrazolo[3,4-b]quinoline, C28H23N3O (P21/c, Z′ = 4), and 11-(3,4,5-trimethoxyphenyl)-10-methyl-8-phenyl-6,8-dihydro-5H-benzo[f]pyrazolo[3,4-b]quinoline, C30H27N3O3, are reported. The crystal structures are compared with those of a number of analogues reported in the recent literature; in particular, structural comparisons are drawn within each series as the substituted pendent aryl group is varied, and between several pairs of strictly isomeric 7-aryl-benzo[h]pyrazolo[3,4-b]quinolines and 11-aryl-benzo[f]pyrazolo[3,4-b]quinolines containing the same aryl substituents within each pair. Intermolecular interactions of the C—H...π type are found in the crystal structures of both series, but π...π stacking interactions are found only in the 7-aryl-benzo[h]pyrazolo[3,4-b]quinoline series. text/html Structural comparisons of isomeric series of 7-aryl-benzo[h]pyrazolo[3,4-b]quinolines and 11-aryl-benzo[f]pyrazolo[3,4-b]quinolines text 1 64 2008-01-17 Copyright (c) 2008 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 72 83 http://scripts.iucr.org/cgi-bin/paper?bm5049 The molecular and supramolecular structures of 18 N-arylpyrazinecarboxamides, Ar NHCO(C4H3N2), have been determined, including the stoichiometric monohydrate of N-(3-methoxyphenyl)pyrazinecarboxamide, and two polymorphs of N-(4-fluorophenyl)pyrazinecarboxamide having Z′ values of 1 and 4, respectively. The aryl groups were selected to include the geometric isomers for a compact range of substituents, namely methyl, trifluoromethyl, fluoro, chloro, methoxy and nitro groups, which exhibit markedly varied electronic properties and markedly varied behaviour as hydrogen-bond donors and acceptors. However, not all isomers in each group could be structurally investigated. A small number of derivatives containing disubstituted aryl groups have also been included in this study. The crystal structures of the solvent-free carboxamides reported here exhibit a wide range of direction-specific intermolecular forces, including N—H...N, N—H...O, C—H...N and C—H...O hydrogen bonds, and π...π stacking interactions, while the structure of N-(3-methoxyphenyl)pyrazinecarboxamide monohydrate also contains O—H...N and O—H...O hydrogen bonds. The resulting supramolecular structures can be zero-, one- or two-dimensional, although no three-dimensional supramolecular aggregation has been observed. In the finite, zero-dimensional structures, pairs of molecules are linked by hydrogen bonds to form cyclic centrosymmetric dimers. The one-dimensional structures include chains formed by the π-stacking of otherwise isolated molecules, simple chains generated by either C—H...O or C—H...N hydrogen bonds, and hydrogen-bonded chains of rings. The two-dimensional structures include examples of both π-stacked hydrogen-bonded chains and hydrogen-bonded sheets. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7681 Wardell, S.M.S.V. de Souza, M.V.N. Vasconcelos, T.R.A. Ferreira, M.L. Wardell, J.L. Low, J.N. Glidewell, C. 2008-01-17 doi:10.1107/S0108768107051804 International Union of Crystallography In N-arylpyrazinecarboxamides, the molecules may be linked into supramolecular structures in zero, one or two dimensions by various combinations of hydrogen bonds, augmented by π...π stacking interactions. Within isomeric series the dimensionality of the supramolecular aggregation appears to be very sensitive to both the identity and the location of the substituent on the N-aryl ring. en supramolecular structures hydrogen bonding electronic properties The molecular and supramolecular structures of 18 N-arylpyrazinecarboxamides, Ar NHCO(C4H3N2), have been determined, including the stoichiometric monohydrate of N-(3-methoxyphenyl)pyrazinecarboxamide, and two polymorphs of N-(4-fluorophenyl)pyrazinecarboxamide having Z′ values of 1 and 4, respectively. The aryl groups were selected to include the geometric isomers for a compact range of substituents, namely methyl, trifluoromethyl, fluoro, chloro, methoxy and nitro groups, which exhibit markedly varied electronic properties and markedly varied behaviour as hydrogen-bond donors and acceptors. However, not all isomers in each group could be structurally investigated. A small number of derivatives containing disubstituted aryl groups have also been included in this study. The crystal structures of the solvent-free carboxamides reported here exhibit a wide range of direction-specific intermolecular forces, including N—H...N, N—H...O, C—H...N and C—H...O hydrogen bonds, and π...π stacking interactions, while the structure of N-(3-methoxyphenyl)pyrazinecarboxamide monohydrate also contains O—H...N and O—H...O hydrogen bonds. The resulting supramolecular structures can be zero-, one- or two-dimensional, although no three-dimensional supramolecular aggregation has been observed. In the finite, zero-dimensional structures, pairs of molecules are linked by hydrogen bonds to form cyclic centrosymmetric dimers. The one-dimensional structures include chains formed by the π-stacking of otherwise isolated molecules, simple chains generated by either C—H...O or C—H...N hydrogen bonds, and hydrogen-bonded chains of rings. The two-dimensional structures include examples of both π-stacked hydrogen-bonded chains and hydrogen-bonded sheets. text/html Patterns of hydrogen bonding in mono- and di-substituted N-arylpyrazinecarboxamides text 1 64 2008-01-17 Copyright (c) 2008 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 84 100 http://scripts.iucr.org/cgi-bin/paper?bs5052 The compounds chlorothiazide and hydrochlorothiazide (crystalline form II) have been studied in their fully hydrogenous forms by powder neutron diffraction on the GEM diffractometer. The results of joint Rietveld refinement of the structures against multi-bank neutron and single-bank X-ray powder data are reported and show that accurate and precise structural information can be obtained from polycrystalline molecular organic materials by this route. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7681 Leech, C.K. Fabbiani, F.P.A. Shankland, K. David, W.I.F. Ibberson, R.M. 2008-01-17 doi:10.1107/S010876810705687X International Union of Crystallography The compounds chlorothiazide and hydrochlorothiazide (crystalline form II) have been studied in their fully hydrogenous forms by neutron powder diffraction on the GEM diffractometer. The results of joint Rietveld refinement of the structures against multi-bank neutron and single-bank X-ray powder data are reported. en neutron powder diffraction thiazides diuretic agents The compounds chlorothiazide and hydrochlorothiazide (crystalline form II) have been studied in their fully hydrogenous forms by powder neutron diffraction on the GEM diffractometer. The results of joint Rietveld refinement of the structures against multi-bank neutron and single-bank X-ray powder data are reported and show that accurate and precise structural information can be obtained from polycrystalline molecular organic materials by this route. text/html Accurate molecular structures of chlorothiazide and hydrochlorothiazide by joint refinement against powder neutron and X-ray diffraction data text 1 64 2008-01-17 Copyright (c) 2008 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 101 107 http://scripts.iucr.org/cgi-bin/paper?bk5067 It is our hypothesis that fluoro substitution provides a powerful tool to modulate the desired characteristics and to increase the specificity of studies of structure–activity relationships. 4-Bromodiphenyl ether (PBDE 3) and its five corresponding monofluorinated analogues (F-PBDEs 3) have been synthesized and fully characterized (using 1H, 13C and 19F NMR spectroscopy, and mass spectrometry). The accurate structure from X-ray crystal analysis was compared with iterative calculations using semi-empirical self-consistent field molecular-orbital (SCF-MO) models. The compounds studied were 4-bromodiphenyl ether (PBDE 3), the 13C6-isotopically labeled PBDE 3 (13C6-PBDE 3) and 2-fluoro-4-bromodiphenyl ether (3-2F), 2′-fluoro-4-bromodiphenyl ether (3-2′F), 3-fluoro-4-bromodiphenyl ether (3-3F), 3′-fluoro-4-bromodiphenyl ether (3-3′F), and 4′-fluoro-4-bromodiphenyl ether (3-4′F). Solid-state intermolecular interactions for PBDE 3 and the F-PBDEs 3 isomers are dominated by weak C—H(F,Br)...π and C—H...F interactions. The C—F bond lengths varied between 1.347 (2) and 1.362 (2) Å, and the C4—Br bond length between 1.880 (3) and 1.904 (2) Å. These bond lengths are correlated with electron-density differences, as determined by 13C shifts, but not with the strength of the C—F couplings. The interior ring angles of ipso-fluoro substitution increased (121.9–124.0°) as a result of hyperconjugation, a phenomenon also predicted by the calculation models. An attraction between the vicinal fluoro and halo substituents (observed in fluoro substituted chlorobiphenyls) was not observed for the bromo substituted F-PBDEs. The influence of a fluoro substituent on the conformation was only observable in PBDEs with di-ortho substitution. Calculated and observed torsion angles showed a positive correlation with increasing van der Waals radii and/or the degree of substitution for mono- to tetra-fluoro, chloro, bromo and methyl substitutions in the ortho positions of diphenyl ether. These findings utilizing F-tagged analogues presented here may prove fundamental to the interpretation of the biological effects and toxicities of these persistent environmental pollutants. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7681 Klösener, J. Swenson, D.C. Robertson, L.W. Luthe, G. 2008-01-17 doi:10.1107/S0108768107067079 International Union of Crystallography Using X-ray structure analysis, electron-density determinations by 13C chemical shifts and semi-empirical calculations we have investigated the structural characteristics of fluorine-tagged polybrominated diphenylethers (PBDEs). Fluorine tagging is a useful tool to provide information about the conformation of the PBDEs. This approach will provide valuable information about the potential biological activities and toxicities of these pollutants. en fluoro substitution structure–activity relationships molecular-orbital models solid-state intermolecular interactions It is our hypothesis that fluoro substitution provides a powerful tool to modulate the desired characteristics and to increase the specificity of studies of structure–activity relationships. 4-Bromodiphenyl ether (PBDE 3) and its five corresponding monofluorinated analogues (F-PBDEs 3) have been synthesized and fully characterized (using 1H, 13C and 19F NMR spectroscopy, and mass spectrometry). The accurate structure from X-ray crystal analysis was compared with iterative calculations using semi-empirical self-consistent field molecular-orbital (SCF-MO) models. The compounds studied were 4-bromodiphenyl ether (PBDE 3), the 13C6-isotopically labeled PBDE 3 (13C6-PBDE 3) and 2-fluoro-4-bromodiphenyl ether (3-2F), 2′-fluoro-4-bromodiphenyl ether (3-2′F), 3-fluoro-4-bromodiphenyl ether (3-3F), 3′-fluoro-4-bromodiphenyl ether (3-3′F), and 4′-fluoro-4-bromodiphenyl ether (3-4′F). Solid-state intermolecular interactions for PBDE 3 and the F-PBDEs 3 isomers are dominated by weak C—H(F,Br)...π and C—H...F interactions. The C—F bond lengths varied between 1.347 (2) and 1.362 (2) Å, and the C4—Br bond length between 1.880 (3) and 1.904 (2) Å. These bond lengths are correlated with electron-density differences, as determined by 13C shifts, but not with the strength of the C—F couplings. The interior ring angles of ipso-fluoro substitution increased (121.9–124.0°) as a result of hyperconjugation, a phenomenon also predicted by the calculation models. An attraction between the vicinal fluoro and halo substituents (observed in fluoro substituted chlorobiphenyls) was not observed for the bromo substituted F-PBDEs. The influence of a fluoro substituent on the conformation was only observable in PBDEs with di-ortho substitution. Calculated and observed torsion angles showed a positive correlation with increasing van der Waals radii and/or the degree of substitution for mono- to tetra-fluoro, chloro, bromo and methyl substitutions in the ortho positions of diphenyl ether. These findings utilizing F-tagged analogues presented here may prove fundamental to the interpretation of the biological effects and toxicities of these persistent environmental pollutants. text/html Effects of fluoro substitution on 4-bromodiphenyl ether (PBDE 3) text 1 64 2008-01-17 Copyright (c) 2008 International Union of Crystallography Acta Crystallographica Section B: Structural Science research papers 108 119 http://scripts.iucr.org/cgi-bin/paper?so5010 A novel idea of employing genetic programming to obtain mathematical expressions representing the dependency of lattice constants (LC) on their atomic parameters is presented in this paper. The results obtained from simulations reveal that only two atomic parameters are sufficient for LC prediction of GdFeO3-type perovskites. In addition, an advantage of this approach is that there is no need to save any trained model as in the case of other existing machine-learning based approaches. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7681 Khan, A. Javed, S.G. 2008-01-17 doi:10.1107/S0108768107057527 International Union of Crystallography This work correlates the lattice constant of GdFeO8-type perovskites with the ionic radii of the cations using genetic programming. The resultant prediction models of the lattice constant are in the form of mathematical expressions. en lattice constants perovskites genetic programming atomic parameters A novel idea of employing genetic programming to obtain mathematical expressions representing the dependency of lattice constants (LC) on their atomic parameters is presented in this paper. The results obtained from simulations reveal that only two atomic parameters are sufficient for LC prediction of GdFeO3-type perovskites. In addition, an advantage of this approach is that there is no need to save any trained model as in the case of other existing machine-learning based approaches. text/html Predicting regularities in lattice constants of GdFeO3-type perovskites text 1 64 2008-01-17 Copyright (c) 2008 International Union of Crystallography Acta Crystallographica Section B: Structural Science short communications 120 122 http://scripts.iucr.org/cgi-bin/paper?pf0063 Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7681 Hargittai, I. 2008-01-17 doi:10.1107/S0108768107061265 International Union of Crystallography en book review text/html The Periodic Table: Its Story and Its Significance. By Eric R. Scerri. New York: Oxford University Press 2007. Pp. xxii + 346. Price (hardback) £19.99. ISBN-13: 978-0-19-530573-9. text 1 64 2008-01-17 Copyright (c) 2008 International Union of Crystallography Acta Crystallographica Section B: Structural Science book reviews 123 124 http://scripts.iucr.org/cgi-bin/paper?me0350 Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7681 Strickland, P.R. 2008-01-17 doi:10.1107/S0108768107052883 International Union of Crystallography Notes for authors. en Notes for authors text/html Notes for authors 2008 text 1 64 2008-01-17 Copyright (c) 2008 International Union of Crystallography Acta Crystallographica Section B: Structural Science international union of crystallography 125 130