issue contents

ISSN: 2052-5206

February 2007 issue

Highlighted illustration

Cover illustration: The cover illustration represents the high- and incommensurately modulated room-temperature phases of Na2CO3 and its reconstructed reciprocal (h2lm) layer ([gamma]-Na2CO3; Dusek et al. (2003). Acta Cryst. B59, 337-352]. Main reflections (open circles) and satellites aligned along parallel lines are indicated. A comparison of the two structures represented by slices parallel to the vertical axis c illustrates their relationship [Arakcheeva & Chapuis (2005). Acta Cryst. B61, 601-607]. [beta]-Na2CO3 at 746 K (C2/m; pseudohexagonal) is shown on the left. All C and Na atoms closer than 3.12 Å are linked. The corresponding non-periodic slice of [gamma]-Na2CO3 indicates how the modulation creates additional close contacts (Ivan Orlov's design is kindly acknowledged).


Acta Cryst. (2007). B63, 1-3
doi: 10.1107/S0108768106048257

research papers

Acta Cryst. (2007). B63, 4-16
doi: 10.1107/S0108768106051652
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Temperature-dependent structural changes of the quasi-one-dimensional compound Cu2Fe2Ge4O13 were evaluated from powder and single-crystal X-ray data between 10 and 900 K. 57Fe Mössbauer spectroscopy between 20 and 298 K provides supplementary data relating to the magnetic properties of the title compound.

Acta Cryst. (2007). B63, 17-25
doi: 10.1107/S0108768106039462
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The crystal structures of the composite-type compounds NaxCuO2 are compared for incommensurate, x = 1.58 and 1.62, and commensurate, x = 1.6, compositions.

Acta Cryst. (2007). B63, 26-36
doi: 10.1107/S0108768106041929
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Two new non-isostructural titanates with the composition SrLiMTi4O11 (M = Cr, Fe) were discovered and their structures were determined using single-crystal X-ray and neutron powder diffraction. Both structures were described in terms of close-packed Sr—O compact planes and relationships between them were established.

Acta Cryst. (2007). B63, 37-48
doi: 10.1107/S0108768106045538
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The constraining of crystal-chemical Rietveld refinements of vanadate phosphate fluorapatites for two oxygen–metal–oxygen angles extracted by ab initio modeling produces experimental results in agreement with quantum ones and residuals similar to unconstrained refinements. Expansion of the BO4 tetrahedra and rotation of Ca–Ca–Ca triangular units is observed upon replacement of phosphorus by vanadium.

Acta Cryst. (2007). B63, 49-55
doi: 10.1107/S0108768106041681
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The topological analysis of the electron density in datolite, Ca[BOH(SiO4)], was carried out using accurate X-ray diffraction data.

Acta Cryst. (2007). B63, 56-62
doi: 10.1107/S0108768106040109
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The crystal structure of EMM-8, the calcined form of SSZ-51, was determined by the combined use of synchrotron powder diffraction, electron diffraction and solid-state NMR.

Acta Cryst. (2007). B63, 63-68
doi: 10.1107/S0108768106046465
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The crystal structures of novel Li4Tt2D (Tt = Si and Ge) ternary hydrides were solved using neutron powder diffraction data. All hydrogen atoms were found to occupy Li6-octahedral interstices.

Acta Cryst. (2007). B63, 69-74
doi: 10.1107/S0108768106045381
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High sensitivity to the presence of mirror symmetry has been found in HOLZ reflections from convergent-beam electron diffraction patterns tilted away from the major zone axes. This sensitivity has been used to re-examine the space groups of LaAlO3 and GdAlO3 perovskites and has relevance for the more precise observation of screw and glide operators.

Acta Cryst. (2007). B63, 75-80
doi: 10.1107/S0108768106044843
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X-ray powder diffractometry has been used in conjunction with IR spectroscopy, thermogravimetry and mass spectrometry to establish the solid-state structure of the [{Pd(μ-OH)(phpy)}2] [phpy = 2-(2-pyridyl)phenyl] complex. It adopts a planar conformation forming trimers created by groups of parallel molecules.

Acta Cryst. (2007). B63, 81-92
doi: 10.1107/S0108768106041668
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Complex cations of transition metals with thioether macrocycles act as templates for the assembly of a wide range of polyiodide anions and their polyanionic networks.

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The 222-cryptand/LiClO4 complex undergoes an orthorhombic unit-cell phase transition at 253 (2) K from the space group P212121 below the transition to P21212 (2c′ = c) above it. A detailed study of the dynamic positional disorder of the Li+ and ClO_4^- ions in the system in the temperature range 100–295 K is presented.

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In isomeric 1-(2-chloronicotinoyl)-2-(nitrophenyl)hydrazines, the molecules may be linked into supramolecular structures in two or three dimensions by various combinations of N—H⋯O, N—H⋯N, C—H⋯N and C—H⋯O hydrogen bonds, sometimes augmented by π⋯π stacking interactions.

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Pressure freezing of ethyl propionate yields the ordered structure, with no group–subgroup symmetry relation with the disordered low-temperature phase.

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Polymorph β of 2,2-aziridinedicarboxamide, originally described in the space group P1, with an exceptionally high Z = 16, has been redetermined in the space group P\overline 1 (Z′ = 8). Comparisons of the structural models and their diffraction patterns have been applied as validation tests.

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The high-pressure crystal structures of 1,2- and 1,3-dichlorobenzene isomers have been determined at room temperature and at 0.18 (5) and 0.17 (5) GPa, respectively. The non-planar association of molecules in these crystals can be rationalized by the electrostatic potential distribution on the molecular surfaces and electrostatic intermolecular interactions.

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A method is presented to classify all structures with saturated hydrogen bonding. Examples are included from the CSD, as are five examples from this study.

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Determination of covalent bond orders and atomic valence indices from the experimental electron density and its derivatives at the bond critical points in a series of organic compounds has been described.

short communications

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The crystal structures at low temperature of four electron-transfer complexes of the M-N2S2 type are reported. The nickel and copper complexes show an unusual tetrahedral coordination, whereas the palladium and platinum complexes show the more conventional square-planar coordination.

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The crystal structure of Cu3MgCl2(OH)6 consists of sheets of edge-sharing Cu(OH)4Cl2 and Mg(OH)6 octahedra, weakly linked by Cl—H bonds. Based on the structural data of similar compounds, the bond-valence parameters of hydroxychlorides have been redetermined.

addenda and errata

Acta Cryst. (2007). B63, 161
doi: 10.1107/S0108768106055753

international union of crystallography

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