issue contents

ISSN: 2052-5206

February 2008 issue

Highlighted illustration

Cover illustration: The cover picture shows the strong and highly structured diffuse scattering from polymorph (II) of N-(p-methylbenzylidene)-p-methylaniline (MeMe) and indicates strongly correlated molecular motion not apparent from the Bragg analysis. Unlike polymorphs (I) and (III), which are disordered, polymorph (II) appears from Bragg scattering to be a perfectly normal ordered molecular crystal. The section of diffuse scattering data shown is part of a full three-dimensional data set recorded on beamline 1-ID-C at the Advanced Photon Source at Argonne, Illinois. Courtesy of Professor T. R. Welberry and Andrew Beasley.

research papers

Acta Cryst. (2008). B64, 1-11
doi: 10.1107/S0108768107059642
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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.

Acta Cryst. (2008). B64, 12-25
doi: 10.1107/S010876810705923X
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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.

Acta Cryst. (2008). B64, 26-33
doi: 10.1107/S0108768107059800
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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.

Acta Cryst. (2008). B64, 34-41
doi: 10.1107/S0108768107066402
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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.

Acta Cryst. (2008). B64, 42-49
doi: 10.1107/S0108768107055292
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A detailed charge-density study of the two energetic materials CL-20 and FOX-7 is presented.

Acta Cryst. (2008). B64, 50-56
doi: 10.1107/S0108768107059629
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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.

Acta Cryst. (2008). B64, 57-65
doi: 10.1107/S0108768107067341
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Cluster analysis has been applied to pyranose sugars found in the Cambridge Structural Database.

Acta Cryst. (2008). B64, 66-71
doi: 10.1107/S0108768107065895
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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.

Acta Cryst. (2008). B64, 72-83
doi: 10.1107/S0108768107065743
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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.

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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.

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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.

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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.

short communications

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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.

book reviews

international union of crystallography

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