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Journal logoSTRUCTURAL SCIENCE
CRYSTAL ENGINEERING
MATERIALS
ISSN: 2052-5206

June 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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Multi-temperature electron density measurements of the Kondo crystal CeB6 and analysis based on a spin-orbit interaction model revealed an entropy-driven mechanism of the 4f-electron transfer from Ce to B—B bonds connecting B6 octahedra. The charge accumulation changes the effective atomic potentials, which causes large anharmonic vibrations of Ce and B at low temperature and an increase in entropy.

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The crystal structure and phase stability of CuSe polymorphs under pressure is investigated using density functional formalism.

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Aragonite has previously been described in the space group Pnma. In this work, weak reflections that violate the systematic extinctions of Pnma are shown to be Bragg reflections. A twinned triclinic model is proposed that goes some way towards explaining these weak reflections.

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To compare densities or porosities of inorganic phases of almost any kind, the anion packing density is introduced and compared with the framework density used by zeolite scientists. It becomes evident that the Shannon–Prewitt effective ionic radii are inadequate to quantitatively describe inroganic structures at high pressures.

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Structural, multipole and orbital analyses of the electron density for the title complex using high-resolution X-ray diffraction data collected at 120 K have been performed. Analysis of the atomic charges indicates the possibility of nucleophilic addition reaction.

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The crystal and electronic structures of a new polymorphous metallic modification of the (ET)2[KHg(SCN)4] salt have been determined, using X-ray diffraction and tight-binding band structure calculations.

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Two examples of the refinement of obverse/reverse twinned structures are discussed. The second example shows additional merohedral twinning.

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Bis(arene)chromium fulleride [Cr(C7H8)2]+C60 exhibits a reversible first-order phase transition forming (C60)22− dimers. The structures of the high- and low-temperature phase are determined via high-resolution X-ray powder diffraction and are compared with the structures of Rb+C60, the other prominent example in which (C60)22− dimers are present.

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By a least-squares fit the average volume of elements in organic and metal-organic crystals is determined as a function of the temperature and a method for fast density estimation and its mean error is presented.

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Racemic crystals of three optically active molecules formed by saturated five-, six- and seven-membered rings bearing two vicinal (either cis or trans) hydrogen-bond donor/acceptor functions were found to represent a novel form of supramolecular close packing. It had been predicted on the basis of five related patterns of close packing revealed in analogous cyclopentane derivatives.

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The structures of two modulated phases of a small organic molecule have been determined. The structure at 295 K has five mirror-symmetric molecules in the asymmetric unit; four of the molecules are disordered. At 130 K the unit cell and asymmetric unit are smaller and the structure is ordered.

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Two L-Val-L-Phe structures present unique dipeptide conformations and crystal packing arrangements, provide comprehensive hydrogen-bond data and display detailed interactions between hydrophobic groups and solvent water molecules.

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The crystal structure and charge density of hydrogen [(2,4-diaminopyrimidin-1-io)methyl]phosphonate monohydrate have been determined by means of single-crystal X-ray diffraction. Preferential polarization of lone-pair electron densities of hydrogen-bond acceptor atoms into shorter hydrogen bonds was observed.

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

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The synthesis and crystal structures of N3P3Cl5[N(CH2Ph)2], N3P3Cl4[N(CH2Ph)2]2, N3P3Ph2Cl3[N(CH2Ph)2] and N3P3Ph2Cl2[N(CH2Ph)2]2 are reported. These compounds are included in two series of crystal structures that are used to investigate steric and electronic effects in substituted cyclophosphazenes.

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All three isomers of the title compound form crystalline complexes with hexamethylbenzene. For each isomer there is at least one complex in which the title compound forms a pseudo-hexagonal two-dimensional layer in which every nitrile group is in contact with Cl atoms in two adjacent molecules.

addenda and errata


Acta Cryst. (2002). B58, 564
doi: 10.1107/S0108768102003506



Acta Cryst. (2002). B58, 565
doi: 10.1107/S010876810200890X
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