issue contents

ISSN: 2052-5206

February 2002 issue

Highlighted illustration

Cover illustration: The structure of remacemide nitrate (C17H21N2O+·NO3-) solved from powder diffraction data using a global optimization approach based on maximum likelihood. Only the remacemide molecule is optimized while the nitrate ion is treated as an unknown blur [Markvardsen, David & Shankland, Acta Cryst. (2002), A58. Submitted]. Image produced by Dr A. Florence, University of Strathclyde, Scotland, using POV-ray 3.1.

research papers

Acta Cryst. (2002). B58, 1-7
doi: 10.1107/S0108768101017918
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Single crystals of tetragonal β-Ta could be obtained from electrodeposition in a bath of molten fluorides. This σ-phase-type structure has been refined in space group P\bar 421m from normal temperature and pressure X-ray data. This structure exhibits many features common to the high-pressure phases of BaIV, BiIII and RbIV.

Acta Cryst. (2002). B58, 8-33
doi: 10.1107/S0108768101018936
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The structure of the basic decagonal phase of Al–Co–Ni has been solved by applying the atomic surface modelling method to refine a high-resolution synchrotron X-ray data set. A solution proposed for the 8 Å superstructure is compared with several earlier models, showing significant differences and solving some apparent contradictions. The stabilization mechanism of quasicrystals appears to be energetic but assisted by entropy.

Acta Cryst. (2002). B58, 34-37
doi: 10.1107/S0108768101017062
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SrMgF4 is predicted to be a new ferroelectric, with a Curie temperature of ∼1450 K and a spontaneous polarization of ∼11 × 10−2 C m−2, on the basis of its recently published crystal structure.

Acta Cryst. (2002). B58, 38-51
doi: 10.1107/S0108768101019310
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Cations in oxides tend to reproduce the structure of their corresponding alloys. In many instances, the structure adopted is that of the high-pressure phases of the alloys, but when oxides are heated (a way of eliminating the pressure effects) the cations recover the structure of the ambient pressure phases of the alloys. An analogy between oxidation and pressure is established.

Acta Cryst. (2002). B58, 52-61
doi: 10.1107/S0108768101016688
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The crystal and molecular structures of tetrakis(trimethylstannyl)germane, Ge(Sn(CH3)3)4, and tetrakis(trimethylstannyl)silane, Si(Sn(CH3)3)4, have been determined for low- and high-temperature phases by Rietveld refinement. Dynamical aspects of the phase transitions have been characterized by NMR.

Acta Cryst. (2002). B58, 62-77
doi: 10.1107/S0108768101017128
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Some 60 examples of crystal structures are presented which can be better described in space groups different from those used in the original publications.

Acta Cryst. (2002). B58, 78-93
doi: 10.1107/S010876810101850X
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In complexes [Ni(cyclam)(OCOR)2], where (RCOO) represents an aromatic carboxylate or dicarboxylate(2−) anion, the (RCOO) acts as a monodentate ligand to Ni, and hard hydrogen bonds of N—H⋯O and O—H⋯O types can link the neutral complexes into supramolecular arrays in one, two or three dimensions.

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In iodo-nitroarenesulfonamides of the type RNH(SO2R′) or RN(SO2R′)2 the supramolecular aggregation can exhibit four types of hydrogen bond, N—H⋯O(nitro), N—H⋯O=S, C—H⋯O(nitro) and C—H⋯O=S; three types of I⋯O interaction, involving two- or three-centre I⋯O2N interactions or I⋯O=S interactions; and aromatic π⋯π interactions. The resulting supramolecular structures can be one-, two- or three-dimensional.

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The primary nitramino group acts as a proton donor in hydrogen bonds formed with the weak proton acceptors of the nitro or sulfonyl group.

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At room temperature the two title compounds are isomorphous with a disordered structure that includes a major component and a minor component, the 6-halo isomer, occurring at the same site in the crystal. When the bromo compound is cooled, it undergoes a second-order phase transition at 282 K to a second polymorph.

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Two phase transitions driven by the conformational transformations of the lactone ring in 6-hydroxy-4,4,5,7,8-pentamethyl-3,4-dihydrocoumarin molecules have been observed: the transition at 225 K is first-order and that at 300 K is a continuous phase transition. Crystal structures and calorimetric studies in the range 110–330 K, and the intriguing relationships between the molecular conformation and crystal symmetry, are reported.

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The crystal structures of β-1,2,3-tris(pentadecanoyl)glycerol (β-C15C15C15), β-1,2,3-tris(heptadecanoyl)glycerol (β-C17C17C17) and β-1,2,3-tris(nonadecanoyl)glycerol (β-C19C19C19) have been determined from high-resolution X-ray powder diffraction data using grid search and Rietveld refinement, resulting in final Rp values of 0.079, 0.065 and 0.070, respectively.

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The asymmetric unit of 4-chloro-2′-biphenylol at 293 and 142 K contains four molecules that do not seem to be related by any approximate symmetry operation. The unusual, and inefficient, crystal packing is a consequence of the ortho position of the hydroxyl substituent. A link between large values of Z′, poor crystal packing and the likelihood of solid-state compound formation is suggested.

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The crystal and electronic structures of ET(NCS)0.77 have been determined, using an X-ray diffraction method and tight-binding band structure calculations. The ET(NCS)0.77 salt has a partial three-dimensional architecture of intermolecular interactions, that is a very rare phenomenon in molecular conductors.

addenda and errata

books received

Acta Cryst. (2002). B58, 154
doi: 10.1107/S0108768101014835

international union of crystallography

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