issue contents

ISSN: 2052-5206

August 2011 issue

Highlighted illustration

Cover illustration: The cover picture highlights an artefact in the electrostatic potential of the macrolide antibiotic roxithromycin as derived via multipole refinement of X-ray diffraction data.  Ignoring the hydrogen disorder (left) in the oxime chain leads to a falsely positive electrostatic potential there as a result of the multipole model's being flexible enough to fit the averaged electron density.  If the invariom formalism, which uses theoretical electron density, is applied to the disordered region (right) the artefact disappears.  A procedure for obtaining reliable electron density distributions in the presence of disorder has been proposed [Holstein et al. (2010). Acta Cryst. B66, 568-577].

feature articles

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Common fundamental structural building principles are discussed for complex intermetallics with giant unit cells and symmetries F\bar{4}3m, Fd\bar{3}m, Fd\bar{3}, Fm\bar{3}m and Fm\bar{3}c.

research papers

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CaSeO4·0.625H2O was synthesized under hydrothermal conditions. The crystal structure was solved by single-crystal diffraction, and thermal and vibrational properties were analysed.

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Polyhedral volume ratios in 15 tilted perovskite structures are expressed in terms of symmetry-adapted mode amplitudes and tilt angles around three pseudo-cubic axes.

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Peculiarities of the electronic structure of bis(µ2-2-(dimethylamino)ethoxo-N,O,O)-di(phenolato-O)ditin(II) and, particularly, of the electron lone pair of tin have been investigated in the gas phase and the solid state with Bader's `Atoms in Molecules' theory.

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The experimental charge density was studied to explore the electronic origin of the unexpected magnetic behaviour of a cobalt molecular complex.

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An improved algorithm has been written for assigning chemical structures to incoming entries to the Cambridge Structural Database.

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The molecular and crystal structure of crystalline ClC(O)SCH2CH3 was obtained by low-temperature X-ray diffraction. A joint analysis of experimental and theoretical data based on AIM theory and NBO population analysis was performed.

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The crystal structure of the metastable polymorph C of nifedipine [3,5-dimethyl 2,6-dimethyl-4-(2-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate] was determined by means of ab initio direct-space methods applied to synchrotron powder diffraction data. Additionally, the crystallization kinetics and thermal stability of the nifedipine system were examined in-situ.

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Free R-factor calculations were used to define the optimal weights on symmetry and similarity restraints in the experimental charge-density analysis of a small organic compound with two molecules in the asymmetric unit. An anharmonic model was applied to the N atoms of the amino groups and to one nitro group in order to account for the high residual density peaks in harmonic refinement and to obtain a better charge-density model.

addenda and errata

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