issue contents

ISSN: 2052-5206

February 2006 issue

Highlighted illustration

Cover illustration: Room-temperature structure of the cation-deficient perovskite, Nd0.7Ti0.9Al0.1O3 [Zhang et al. (2006). Acta Cryst. B62, 60-67>]. The superlattice peaks associated with out-of-phase octahedral tilting (shown) have intensities consistent with tilting around the x and y axes (sum of a- and c-), but tilting around the y axis (contribution b-) evidently does not occur. The tilt system in Glazer's notation is thus a-b0c-, and the space group and structure are found from the tree displayed. Two views of the structure are shown - the (TiAl)O6 are shown as octahedra, the Ti/Al atom being visible within them, and the darker and lighter spheres outside these octahedra represent fully and partly occupied layers of Nd, respectively. The octahedral tilting, around both x and y axes, is clearly seen.

research papers

Acta Cryst. (2006). B62, 1-8
doi: 10.1107/S010876810503764X
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The Ti2Ni structure type emerges as a consequence of the competition between face-centred cubic translational and icosahedral-face orientational ordering of the 16(c) first coordination clusters along regular tetrahedron edge directions.

Acta Cryst. (2006). B62, 9-15
doi: 10.1107/S0108768105037985
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The Jahn–Teller and non-Jahn–Teller distortions are reviewed within the same context. The origin and the influence of the magnitude of polyhedral elongations on physical properties are discussed for the superconductor cuprates and the CMR manganites.

Acta Cryst. (2006). B62, 16-25
doi: 10.1107/S0108768105035779
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Two closely related quasicrystal approximants are expected to have similar crystallographic structure-factor amplitudes and phases for the strong reflections so the structure of an unknown quasicrystal approximant can be solved from a related known quasicrystal approximant. This strong-reflections approach is applied to the new τ(μ)-AlCrSi phase and a structure model of τ(μ) is deduced from the structure of the related λ-Al4Mn phase.

Acta Cryst. (2006). B62, 26-41
doi: 10.1107/S0108768105040577
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Eighteen of a total 52 inorganic structure types with R3 symmetry are shown to satisfy the criteria for ferroelectricity. As many as 46% of those initially reported in the space group R3, 35% of those currently assigned, most likely exhibit higher symmetry.

Acta Cryst. (2006). B62, 42-51
doi: 10.1107/S0108768105038784
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Hydrothermal synthesis and structural analysis of the zeolite-like lithosilicate RUB-30 (K2.6Li5.4[Li4Si16O38]·4.3H2O) are reported. Two different structure types are proposed based on the observation of unusual superstructure reflections and diffuse streaks.

Acta Cryst. (2006). B62, 52-59
doi: 10.1107/S0108768105034671
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Based on the superspace approach we present a method to generate a family of modular structures, provided that one of its members exhibits an incommensurately modulated (i.e. aperiodic) structure. This approach, which relies on the variation of the modulation vector q, is illustrated with the generation of the K5Yb(MoO4)4 family and the analysis of its temperature-dependent phase transformations.

Acta Cryst. (2006). B62, 60-67
doi: 10.1107/S0108768105041066
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The room-temperature structure of the cation-deficient perovskite, Nd0.7Ti0.9Al0.1O3, with layered ordering of cations/vacancies on the A-site, involves octahedral tilting around two axes. Tilting around the axis parallel to the direction of the layered cation/vacancy ordering disappears above ca 750 K, the only tilt persisting at higher temperature being about a single axis perpendicular to this direction.

Acta Cryst. (2006). B62, 68-85
doi: 10.1107/S0108768105036931
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Crystals of the three actinide complexes [M(M′O4)4(TBPO)4], where MM′ = URe, ThRe, ThTc, respectively, studied between 293 and 100 K, show a number of reversible crystal-to-crystal phase transitions. The increase of order and differences in conformations of the complexes seen at the lower temperatures arise from a combination of the freezing of the nBu groups, the differing packing constraints of the various space groups and the network of weak C—H⋯O intra- and intermolecular hydrogen bonds.

Acta Cryst. (2006). B62, 86-93
doi: 10.1107/S0108768105037766
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A new β-phase of (CH3)3SiCl obtained by pressure freezing is strikingly similar to the α-phase obtained by cooling. In neither of these structures are Cl⋯Cl contacts shorter than 4.9 Å.

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The crystal structure of benzene in phase I, space group Pbca, has been determined at 0.30, 0.70 and 1.10 GPa, and 296 K. Short H⋯C contacts explain the exceptional resistance of benzene to polymerization.

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The crystal structure of kinetin dihydrogenphosphate has been determined at various temperatures providing evidence for the polymorphic phase transition at 291.1 K. The dynamic equilibrium between the different tautomeric forms of the adenosine residue is observed in the low-temperature phase.

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Seven 3,5-dihalo-4-hydroxybenzonitrile compounds form chains as a consequence of OH⋯NC interactions. In the case of the bromo and iodo compounds the chains assemble into layers through XX contacts with two-dimensional isostructurality among the compounds.

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The crystal structure of 1-formyl-3-thiosemicarbazide was re-elucidated at room temperature, 100 and 90 K, and all the intermolecular interactions were characterized by the topological analysis of the electron density.

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Changes in the crystal structure were monitored throughout the course of an intramolecular single-crystal to single-crystal Yang photocyclization reaction by means of X-ray diffraction. The results are compared with analogous data for intermolecular solid-state reactions.

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Structural X-ray and 1H NMR investigations as well as DFT calculations provide evidence that the course of the reaction of substituted benzaldehyde with 2-oxo-2,3-dihydro-1H-imidazo[1,2-a]pyridinium cation is different in protic and polar aprotic solvents, and depends on the character and the position of the substituent in the benzaldehyde. Both theory and experiment point to the benzylidene derivatives as possessing higher photoinitiating ability than their benzyl analogues.

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Variable-temperature X-ray diffraction and differential scanning calorimetry experiments have been performed for p-nitrophenol polymorphs. Crystal structures, interactions and thermodynamics in the polymorphs of p-nitrophenol have been compared with those corresponding to the polymorphs of m-nitrophenol.

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The neutron diffraction analysis of the photoisomerization of a partially deuterated achiral α,β-unsaturated thioamide to form a chiral β-thiolactam in the crystalline state revealed the direction and the process of deuterium transfer by determination of an absolute configuration of a produced chiral methylene, —C*HD—.

short communications

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Synchrotron X-ray powder diffraction work demonstrated that there existed two phases of oxygen-deficient tetragonal ZrO2 − δ [average particle size: 11 ± 2 nm, δ = 0.031 (7)] and monoclinic ZrO2 (average particle size: 24 ± 4 nm) in a nano-sized zirconium oxide sample. MEM electron-density distribution was investigated for the tetragonal ZrO2 − δ phase.

addenda and errata

international union of crystallography

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