issue contents

ISSN: 2052-5206

February 2012 issue

Highlighted illustration

Cover illustration: A high-angle annular darkfield scanning transmission electron microscopy image of the decagonal quasicrystal Al72Co8Ni20 overlaid with a structure model. Clusters of type 1 (occupied center) highlight transition metal sites (white spheres) and clusters of type 2 (empty center) possess both transition metal and mixed aluminum/transition metal (red) sites. Decagonal-shaped clusters are outlined and exhibit two types of overlap as a unifying building feature of aperiodic quasicrystals of decagonal Al-Co-Ni, Al-Co-Cu and Al-Fe-Ni [Deloudi et al. (2011). Acta Cryst. B67, 1-17, based on Abe & Tsai (2004) J. Non-Cryst. Solids, 334, 198-201]. The 2011 Nobel prize in chemistry was awarded to D. Shechtman for his discovery of quasicrystals.

research papers

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The crystal structure of a new quenchable high-pressure–high-temperature modification of antimony(III) oxide, γ-Sb2O3, with rare 3,3T8 topology has been determined from high-resolution synchrotron powder diffraction data.

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The lattice parameters of SrTiO3 and DyScO3, and NdGaO3 single crystals have been measured with high precision at room temperature with a relative accuracy of the order of 10−5.

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The crystal structure of the new mineral sarrabusite Pb5CuCl4(SeO3)4 has been solved using a manual and an automated version of the new electron-diffraction tomography technique combined with the precession of the electron beam.

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This paper describes a data-driven strategy using principal component analysis and K-means clustering to discover the best classifiers for constructing structure maps.

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Crystal structures of low- and high-temperature modifications of a binary phase Li2Zn3 were demonstrated by single-crystal X-ray diffraction techniques. The low-temperature modification is a disordered variant of Li5Sn2, space group R\bar 3m. The high-temperature modification crystallizes as an anti-type to Li5Ga4, space group P\bar 3m1. Two polymorphs can be described as derivative structures to binary Li5Ga4, Li5Sn2, Li13Sn5, Li8Pb3, CeCd2 and CdI2 phases.

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In the spin-crossover compound [Fe(ptz)6](BF4)2 six different phases are observed. The low-spin disordered phase was solved in a novel approach to accommodate the very unusual twinning.

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A series of alkali bromanilate salts has been studied. The quinoid rings of hydrogen bromanilate anions stack face-to-face with a short centroid separation of 3.3 Å and no offset.

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The crystal structure of C60·4benzene has been re-examined at 157, 93 and 13 K, and found to undergo an order–disorder phase transition that enables more accurate structural information for the most common fullerene to be obtained at low temperature.

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Novel hydrogen-bridged ring-assisted π-stacking interactions are presented and discussed.

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Diffuse X-ray scattering experiments were performed on single crystals of the two most commonly found polymorphs of paracetamol. Diffraction data calculated from simple Monte Carlo models of these forms are in good agreement with the observed data. Investigation of the models show that disordered displacements similar to that in the real crystal can be generated in a model based solely on knowledge of intermolecular potentials and atomic coordinates obtained from a Bragg diffraction experiment. Comparison of the correlated motions between the crystal forms revealed no further insight into the form (II) → (I) transition.

short communications

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The restrained Rietveld analysis of the crystal structure of magnesium perchlorate tetrahydrate, Mg(ClO4)2(H2O)4 [Robertson & Bish (2010). Acta Cryst. B66, 579–584], is revised. The structure is re-refined in the C2/m space group by the derivative difference method, anisotropically for all non-H atoms and isotropically for H atoms without restraints.

addenda and errata

international union of crystallography

book reviews

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