issue contents

ISSN: 2052-5206

August 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

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The monoclinic phase of the compound InAl1 − xTixO3 + x/2 with x = 0.701 (1) has been studied through single-crystal X-ray diffraction.

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A high-temperature X-ray diffraction study revealed that brownmillerite-type Ca2Al2O5 transforms to an incommensurately modulated structure at elevated temperatures. The characterization is completed by Raman spectroscopy.

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Twelve families with the space group P3m1 are shown to satisfy the structural criteria for, and hence may be predicted to exhibit, the property of ferroelectricity. Sixteen other families are likely to be nonpolar with a similar number having reduced predictive properties.

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A new Sillén–Aurivillius intergrowth Bi4Fe1/3W2/3O8Br has been studied by transmission electron microscopy and associated techniques, along with its structural evolution when heated at high temperature (1473 K).

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Crystal structure analysis of silicon- and germanium-containing compounds within the framework of the stereoatomic model was carried out to distinguish the quantitative descriptors of the intermolecular contacts Si⋯D and Ge⋯D.

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The occupancy and displacive short-range order in HMTA, the adduct of hexamethylenetetramine and azelaic acid, have been examined using X-ray diffuse scattering, determining the ordering of molecular flips and the key intermolecular interactions.

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The following article explores the effect of high pressure on the L-α-glutamine crystal structure. Results show that the main structural feature to be influenced by pressure is the hydrogen bond network.

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3-Aminopropan-1-ol molecules change their conformation from a pseudo-ring in the vapour and liquid to an extended one in the solid state, and the intramolecular hydrogen bonds are replaced with intermolecular ones. The liquid freezes at 0.1 MPa/284 K and at 0.13 GPa/296 K in the same polar monoclinic structure, space group Cc.

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The crystal structure of a 4:1 complex between N-methylpiperidine betaine (N-carboxymethyl-N-methylpiperidinium inner salt) and hexafluorosilicic acid reveals six different dimers of hemiprotonated betaine molecules, formed via very short O⋯H⋯O hydrogen bonds between the carboxylic functions.

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It is shown that hydrogen bonds from O—H and N—H donors to the S acceptors of thioureas and thioamides are relatively longer (by ∼ 0.25 Å) and weaker (by ∼ 12 kJ mol−1) than hydrogen bonds to the analogous O-acceptor compounds.

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X-ray and NMR studies of meso and chiral tartarodinitriles reveal their diverse conformational preferences compared with tartrates and NH-tartramides, and point to the gauche effects, local dipolar and strong intermolecular interactions as structure determining factors.

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A new computer program to search for hydrogen-bond motifs has been developed and used to identify frequent ring and chain motifs in amino-acid crystal structures.

short communications

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The applicability of the Wang–Liebau polyhedron eccentricity parameter in the bond-valence model has been found to be doubtful: the correlations between the values of the polyhedron eccentricity parameters and the bond-valence sums calculated for the cations with one lone electron pair are probably an artifact of the poorly determined bond-valence parameters.

addenda and errata

Acta Cryst. (2008). B64, 519
doi: 10.1107/S0108768108017497
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