issue contents

Journal logoSTRUCTURAL SCIENCE
CRYSTAL ENGINEERING
MATERIALS
ISSN: 2052-5206

April 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


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Metal-atom square nets occur in many rare earth boride carbides and account for their tendency to form twins and intergrown crystals of different phases. The possibilities of structure determinations via X-ray diffraction and electron microscopy on intergrown crystals are discussed.

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Rietveld neutron powder profile analysis of the A-site substituted distorted perovskite compound Na0.5Bi0.5TiO3 (NBT) is reported over the temperature range 5–873 K. Detailed characterization of the phase transition sequence occurring in this compound has been made. The general trends of cation displacements and the deviations of the octahedral network from the prototypic cubic perovskite structure have been established and their systematic behaviour with temperature is reported. The second harmonic generation as a function of temperature has also been made.

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High-resolution X-ray scattering experiments provide detailed information on the intersubsystem bonding in (LaS)1.13TaS2 and (LaS)1.14NbS2. A correlation is revealed between relative positions of the mutually incommensurate subsystems, the displacement modulation and the modulation of the temperature parameters.

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A detailed description of the tubular oxide Bi4Sr12Co8O30−δ is given. [Co4O13] clusters are present and their particular structure is determined; they are one of the basic elements for building [Sr4Co4O13] pillars, well known in this type of phase. A comparison between pillars in the Co and the related Mn tubular oxide, Bi3.6Sr12.4Mn8O30−δ, is given.

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Zirconosilicates and their MT analogs with the frameworks of M octahedra and T tetrahedra (60 minerals and 34 synthetic phases) were first arranged into 41 topological types using coordination sequences of M and T atoms. A procedure is proposed of hierarchical analysis of MT framework structure organization on three levels (atomic, polyhedral and suprapolyhedral), which is based on the concept of polyhedral microensemble.

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A new set of criteria for quantitative analysis of molecular interactions is proposed, which is based on the conceptions of atomic and molecular Voronoi–Dirichlet polyhedra. The set was used to study the influence of steric factors on the stability of complex groups as well as on the presence or absence of agostic contacts in crystal structures of 808 rare-earth π-complexes.

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The different rate constants of photoisomerization from the 2-cyanoethyl group to the 1-cyanoethyl group among three mixed cobaloxime complex crystals with the 2-cyanoethyl group and different pyridine derivatives as axial positions are explained well by the volumes of the reaction cavities. The reaction pathway was directly observed since the isomerization in one of the crystals proceeded with retention of the single-crystal form.

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Prediction provides sets of energetically reasonable crystal structures, from which the actual structure may be deduced by recourse to powder X-ray diffraction data. In this manner, structure prediction becomes a powerful tool for structure solution.

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The complexes trans-[PtCl2(PBz3)2], trans-[PtI2(PBz3)2], trans-[Pt(NCS)2(PBz3)2] and trans-[PdI2(PBz3)2] have been structurally characterized and the differences or similarities in geometry are analysed by half-normal probability plots and RMS calculations.

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A series of inclusion compounds of a diol host with a number of xylidine isomers as guests gave rise to various host:guest ratios controlled by crystallization temperatures. The crystal structures were elucidated by X-ray diffraction. Their thermal characteristics, selectivities of enclathration by the host and kinetics of decomposition were measured.

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The structure of cholesterol above the (304.8 K) phase transition, previously published in preliminary form, has been fully refined using augmented X-ray data.

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In the series of methylester/N-methylamide derivatives of (R,R)-O,O′-dibenzoyl tartaric acid, which utilize the twofold symmetry site in their crystals, the methylester group shows the ability to mimic the N-methylamide substituent. This leads to static disorder and the isostructuralism phenomenon, as well as to the replacement of N—H⋯O by C—H⋯O hydrogen bonds. The molecules of (R,R)-O,O′-dibenzoyltartaric acid diamide form hydrogen-bond patterns typical for amides, but at the expense of their packing efficiency, which results in a series of homeotypic inclusion compounds.

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In salt-type adducts of organic diamines with chiral or racemic tartaric acids, the hard hydrogen bonds can generate sheets, bilayers or three-dimensional frameworks: the supramolecular structures formed by the chiral acid can closely mimic centrosymmetry

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The title compound (I) forms a wide variety of polymorphs and solvates: some of the polymorphs are solvent free, while the solvates may have solvent molecules hydrogen bonded to (I) or simply encapsulated within a framework structure. In some solvates the framework formed by (I) contains continuous channels and solvent molecules may be localized within the channels or intractably disordered within them.

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Highly polarized molecular electronic structures in 2,4,6-trisubstituted-5-nitrosopyrimidines lead to extensive charge-assisted hydrogen bonding.

addenda and errata



Acta Cryst. (2002). B58, 316
doi: 10.1107/S0108768102004421
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