issue contents

ISSN: 2052-5206

August 2010 issue

Highlighted illustration

Cover illustration: The clusters shown on the cover image belong to the fundamental structural building units of cF(5928-x)-Al56.6Cu3.9Ta39.5, x = 20, one representative of a family of cluster-based tantalum copper aluminides with giant unit cells hosting up to more than 20 000 atoms. Their structures can be geometrically described as packings of clusters such as fullerenes, dodecahedra, pentagonal bifrusta, hexagonal bipyramids and Friauf polyhedra [Conrad et  al. (2009). Acta Cryst. B65, 318-325; see also Weber et  al. (2009). Acta Cryst. B65, 308-317].

research papers

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The GeSb6Te10 and GeBi6Te10 intermetallic compounds have 51-layered cubic close-packed stacking structures in common. In these structures the Ge/Sb (Ge/Bi) and Te layers are stacked alternately; Te atoms exclusively occupy their own specific layers, whereas Ge and Sb (Bi) atoms are randomly located at the other layers, causing a partially disordered atomic occupation in these layers.

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Polymorphism and piezochromicity are reported at room temperature in the three-dimensional network-based phosphate RbCuPO4, generated by subtle interplay between copper and phosphate coordination polyhedra. A combination of formula-unit volume reduction and conversion of copper dimer to trimer chains accompanied by changes in the copper coordination number are shown to be responsible for the piezochromicity.

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The structure of the 215 K phase of methylammonium tin bromide is solved, and interplay between hydrogen bonding and lone-pair distortions is examined.

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The compound [Ni(H2O)2(15-crown-5)](HSO4)2 is remarkable for having two non-destructive solid–solid phase transitions in the temperature range 110−295 K. Three related phases [room-, intermediate- and low-temperatures phases (I), (II) and (III)] have been isolated; all phases have similar packing but the Z′ number varies in the sequence (I) ↔ (II) ↔ (III).

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New phosphoramidate compounds have been synthesized and structurally characterized. Their crystal structures reveal that the —C(O)NHP(O)< skeleton shows the syn conformation, in contrast to all similar phosphoro-azo compounds previously reported. The capability for coordinating LnIII ions have been demonstrated and the corresponding complexes have been obtained.

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Pyrazinium hydrogen sulfate is studied as a candidate for a novel ferroelectric material with giant spontaneous polarization.

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No pressure-induced polymorphic transitions in L-alanine could be detected by single-crystal and powder X-ray diffraction at least up to ∼ 12 GPa, although some important changes in the intermolecular interactions occur, which also manifest themselves in the Raman spectra. Two new phases (presumably solvates) of L-alanine could be crystallized from MeOH/EtOH/H2O solution in the pressure range 0.8–4.7 GPa, but only if the sample was kept at these pressures for at least 1–2 d, and converted back to L-alanine on reverse decompression.

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Crystal structures of alkyl-substituted Tröger's base analogues appear to have a tendency for crystallizing in high-Z′ structures. The reasons for this are expanded upon.

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The common organic buffer HEPES [4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid] used widely in biological research has been studied by high-resolution X-ray single-crystal diffraction. An analysis applying the Hansen–Coppens multipole model and Bader's Quantum-Theory-of-Atoms-in-Molecules (QTAIM) yields an accurate description of the electron density distribution in the crystal.
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