issue contents

Journal logoSTRUCTURAL SCIENCE
CRYSTAL ENGINEERING
MATERIALS
ISSN: 2052-5206

December 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].

research papers


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Electron-density profiles indicate the cations to be tetrahedrally shifted from the 8c position into the 32f site of the Fm3m unit cell as a new feature of the fluoroelpasolite structure refinement.

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The crystal structure of LaTi2Al9O19 determined by X-ray powder diffraction is presented together with its dielectric properties. The structure of La3Ti5Al15O37 is critically reviewed.

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High-resolution neutron diffraction of the important piezoelectric lead zirconate titanate (PZT) has found that oxygen disorder exists well into the cubic phase.

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In the presence of high relative air humidity the crystal structure of CaSO4·0.5H2O transforms due to the incorporation of additional water of hydration. The crystal structure of CaSO4·0.625H2O was solved by single-crystal X-ray diffraction at 298 K with 75% relative air humidity.

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Stacking faults in Ca4Fe2Mn0.5Ti0.5O9 have been examined using X-ray diffraction and high-resolution transmission electron microscopy. Electron diffraction revealed two superstructures with ordered stacking sequences.

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The structure of single-crystal [Ni(H2O)6](NO3)2·(15-crown-5)·2H2O has been studied in the range 90–308 K in intervals of ≤ 10 K as the crystal passed through three phase transitions. An unusual intermediate, modulated phase described in a commensurate approximation (Z′ = 7) has been characterized.

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A joint theoretical and experimental investigation of the structure of piracetam, in which the conformational space of piracetam is explored by a scan of the two dihedral angles and predicted conformations with intramolecular hydrogen bonds are compared with CSD geometries. Single crystals and the structure of piracetam are obtained and statistical comparison with CSD forms shows only three dihedral angle families.

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An orthorhombic benzene-silicalite-1 single crystal was obtained from a monoclinic twin crystal, and the structure was determined by a single-crystal method for the first time.

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Distinctive diffuse scattering in the form of diffuse rings around Bragg positions has been observed in the diffraction patterns of a crystal of the N-terminal fragment of the Gag protein from Feline Foamy Virus. It is shown that these are caused by geometric frustration as molecules try to pack on the triangular bc mesh of the space group P6122.

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Dialkyl oxalates are cryocrystallized and the crystal structures have been analysed. The distinctive nature of two oxalates that are solid at room temperature is rationalized on the basis of C—H⋯O interactions.


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Neutron and high-resolution X-ray diffraction experiments at 100 K have been used to derive the precise geometry and the electron density of a wide range of X—H⋯O interactions in the title compound. The shortest O—H⋯O bond does not follow the trend of the remaining hydrogen bonds: it is significantly more symmetric, and energy density criteria support the concept of an interaction with intermediate character between covalent and closed-shell.

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The structural data of two azacoumarins, LD 425 and LD 489, and one 2-quinolone, LD 473, are reported. Bond-length patterns and characteristic spectral blue shifts in these compounds are examined using resonance theory and structural comparisons with their coumarin analogues.

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Weak intermolecular contacts of C—H⋯C(π), C,N(π)⋯C,N(π) and H⋯H types occurring in crystals of isoindole derivatives were analysed in terms of topological electron-density parameters and Hirshfeld surfaces derived from high-resolution X-ray diffraction experiments.
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