Acta Crystallographica Section B

Structural Science

Volume 54, Part 6 (December 1998)

Cover illustration: Space filling representation of the hydrated anionic framework formed by trimesic acid around piles of cobalticinium cations in crystalline [(C5H5)2Co][(H3TMA)(H2TMA)].2H2O. Graphics (picture or drawing) obtained using SCHAKAL by E. Keller, University of Freiburg, Germany. Courtesy of D. Braga and F. Grepioni

• research papers
• short communications
• books received
• international union of crystallography

research papers

Acta Cryst. (1998). B54, 705-713    [doi:10.1107/S0108768198000962]

Room-Temperature Superstructure of ZrV₂O₇

J. S. O. Evans, J. C. Hanson and A. W. Sleight

Synopsis: ZrV₂O₇ and related phases are of interest for their negative thermal expansion properties, but there has been no detailed report of their structures to date. We describe here the room-temperature 3 × 3 × 3 superstructure of ZrV₂O₇, which has been determined from single-crystal synchrotron X-ray data.

Acta Cryst. (1998). B54, 714-721    [doi:10.1107/S010876819800161X]

Pressure-Induced Order-Disorder Phase Transition of Spinel Single Crystals

J. Wittlinger, S. Werner and H. Schulz

Synopsis: Single crystals with the composition Mg_0.4Al_2.4O₄ show a pressure-induced phase transition at 10.7 GPa which is partially reversible on pressure release. The resulting compound reveals a disordering of the cations on the tetrahedral and octahedral sites of the spinel structure.

Acta Cryst. (1998). B54, 722-731    [doi:10.1107/S0108768198003590]

Ideal and Real Structure of Ti₅O₄(PO₄)₄: X-ray and HRTEM Investigations

F. Reinauer and R. Glaum

Synopsis: Pentatitanium tetraoxide tetrakis(phosphate) belongs to the Fe₂O(PO₄) structure family. The relationship is indicated by the formula ₃Ti₅O₄(PO₄)₄. X-ray single-crystal and high-resolution transmission electron microscopy investigations reveal partial disorder of Ti⁴⁺ over eight available octahedral voids. The ideal structure consists of four (TiO)O₅, one TiO₆ and four slightly distorted PO₄ units.

Acta Cryst. (1998). B54, 732-740    [doi:10.1107/S0108768198003759]

Distribution of the M-M Distances in the Rare Earth Oxides

A. Vegas and R. Isea

Synopsis: The cation arrays in rare earth oxides reproduce the topology and distances of the structures of the pure metals.

Acta Cryst. (1998). B54, 741-749    [doi:10.1107/S0108768198003772]

Equation of State of -Al₂O₃ (Corundum) from Quasi-Harmonic Atomistic Simulations

M. Catti and A. Pavese

Synopsis: An interatomic potential is developed for a static and vibrational simulation of -Al₂O₃. Structural, elastic and thermal expansion data are predicted in the p,T domain from 0 to 40 GPa and from 300 to 1700 K.

Acta Cryst. (1998). B54, 750-765    [doi:10.1107/S0108768198003802]

Atomic Structure of PbZrO₃ Determined by Pulsed Neutron Diffraction

S. Teslic and T. Egami

Synopsis: The atomic structure of lead zirconate, PbZrO₃, and its variation with temperature were determined by pulsed neutron diffraction using both Rietveld refinement and atomic pair distribution function analysis. The symmetry at low temperatures was shown to be Pbam and a new antiferroelectric structure was identified for the intermediate phase.

Acta Cryst. (1998). B54, 766-773    [doi:10.1107/S0108768198003905]

New Measure of Distortion for Coordination Polyhedra

E. Makovicky and T. Balic-Zunic

Synopsis: Use of the centroid concept for coordination polyhedra enables comparison of distorted and ideal polyhedra with the same number of coordinated atoms. The relation between the volumes of the distorted and the ideal polyhedra can be used as a global measure of distortion.

Acta Cryst. (1998). B54, 774-781    [doi:10.1107/S0108768198004108]

Multipole Analysis of the Electron Density in Topaz Using X-ray Diffraction Data

Yu. V. Ivanov, E. L. Belokoneva, J. Protas, N. K. Hansen and V. G. Tsirelson

Synopsis: The multipole deformation electron density, Laplacian of the electron density and (3,-1) bond critical point parameters are analyzed in topaz, Al₂[SiO₄]F₂, using accurate X-ray diffraction data.

Acta Cryst. (1998). B54, 782-789    [doi:10.1107/S0108768198004200]

Group-Theoretical Analysis of Octahedral Tilting in Perovskites

C. J. Howard and H. T. Stokes

Synopsis: Simple tilting of the octahedral units in perovskite gives rise to a number of distinct, closely related structures. Fifteen possible space groups are listed along with group-subgroup relationships and an indication of which translations between the different structures are allowed to be continuous.

Acta Cryst. (1998). B54, 790-797    [doi:10.1107/S0108768198005254]

Isotope Effect in TlH₂PO₄ and TlD₂PO₄

S. Ríos, W. Paulus, A. Cousson, M. Quilichini and G. Heger

Synopsis: The phase transitions observed in TlH₂PO₄ and TlD₂PO₄ with decreasing temperature are analysed.

Acta Cryst. (1998). B54, 798-808    [doi:10.1107/S0108768198005436]

Distortion of Crystal Structures of Some Co^III Ammine Complexes. III. Distortion of Crystal Structure of [Co(NH₃)₅NO₂]Cl₂ at Hydrostatic Pressures up to 3.5 GPa

E. V. Boldyreva, D. Yu. Naumov and H. Ahsbahs

Synopsis: The anisotropy of structural distortion of the title compound under pressure was shown to be qualitatively different to that on cooling. The role of non-covalent interactions, in particular hydrogen bonds, in the anisotropy of structural distortion is discussed.

Acta Cryst. (1998). B54, 809-818    [doi:10.1107/S0108768198006351]

Structures of Fluoroarsenates KAsF_6n(OH)_n, n = 0, 1, 2: Application of the Heavy-Atom Method for Modulated Structures

J. Peterková, M. Dusek, V. Petrícek and J. Loub

Synopsis: The structures of the fluoroarsenates KAsF_6-n(OH)_n, n = 0, 1, 2, depend on the number and type of hydrogen bonds; a standard structure, a superstructure and an incommensurate modulated structure are found for n = 0, 1 and 2, respectively. A heavy-atom method developed for modulated structures is used for the solution of the incommensurate structure.

Acta Cryst. (1998). B54, 819-833    [doi:10.1107/S0108768198003954]

Distribution and Topology of the Electron Density in an Aluminosilicate Compound from High-Resolution X-ray Diffraction Data: the Case of Scolecite

S. Kuntzinger, N. E. Ghermani, Y. Dusausoy and C. Lecomte

Synopsis: The Si-O and Al-O bonds in a natural zeolite, scolecite, are characterized by the topological features of the experimental electron density. The estimation of the atomic net charges in this compound is described according to data analysis by the statistical prediction matrix (leverages) method.

Acta Cryst. (1998). B54, 834-850    [doi:10.1107/S0108768198004984]

Carbides Ln₁₀Ru₁₀C₁₉ (Ln = Y, Gd-Lu): Crystal Structure of their Subcells and the Superstructures of Er₁₀Ru₁₀C₁₉

R.-D. Hoffmann and W. Jeitschko

Synopsis: Subcell and superstructures of Er₁₀Ru₁₀C₁₉ are described where various stacking variants arise from an ordered arrangement of single C atoms and C₂ pairs which are situated in trigonal Ru prisms. The Ru and C atoms of the three-dimensionally infinite polyanionic network seem to obey the 18- and 8-electron rules, respectively.

Acta Cryst. (1998). B54, 851-858    [doi:10.1107/S0108768198004637]

Net Intensities: Accuracy Improvement Through a Bayesian Perspective on the Measuring Strategy and Their Persistent Lack of Precision. An Illustration

A. T. H. Lenstra, B. Bracke, B. van Dijk, S. Maes, C. Vanhulle and H. O. Desseyn

Synopsis: The standard error on an intensity can be reduced below counting statistical error margins when, in a fixed time experiment, a repetition of fast profile scans replaces the traditional slow, but single scan. The decrease in intensity errors is not followed by a similar reduction in parameter errors, because the latter are dictated by the randomization of systematic intensity errors.

Acta Cryst. (1998). B54, 859-865    [doi:10.1107/S0108768197017758]

Solid-State Modeling. VI. 2,3-Diketopiperazine: the Integration of Crystallographic and Spectroscopic Evidence

A. T. H. Lenstra, B. Bracke, B. van Dijk, S. Maes, C. Van Alsenoy, H. O. Desseyn and S. P. Perlepes

Synopsis: The crystallographic and spectroscopic analyses of 2,3-diketopiperazine are combined with ab initio calculations for both the gas phase and solid state. The calculated IR shifts for the C=O stretching frequencies, which are hydrogen-bonding dependent, fit with the experimental evidence.

Acta Cryst. (1998). B54, 866-871    [doi:10.1107/S0108768198002171]

Oxime-Carboxyl Hydrogen Bonds: the Preferred Interaction Determining Crystal Packing of `Carboxyoximes'

J. K. Maurin

Synopsis: A statistical analysis of hydrogen-bond interactions formed by oximes and carboxylic acids is presented. Ab initio quantum-chemical calculations have been used to rationalize the observed preference for the oxime-carboxyl interaction compared with carboxyl-carboxyl and oxime-oxime interactions.

Acta Cryst. (1998). B54, 872-876    [doi:10.1107/S0108768198003577]

Energetic Study of the Disordered Solvent in the Crystal Structure of an Isoxazole Derivative

M. Pani, M. M. Carnasciali, A. Mugnoli, P. Beltrame, E. Cadoni and G. Gelli

Synopsis: Packing potential energy calculations for host-guest model crystals account for the disorder of ethyl acetate solvent molecules in the crystal state.

Acta Cryst. (1998). B54, 877-888    [doi:10.1107/S0108768198005114]

Topological Description of Pseudosymmetries in trans-2,3,4,5,5a,6,7,8,9,9a-Decahydro-2-methyl-4-phenylaminocarbonylbenzo[f][1,4]oxazepin-3-one and Other Structures which Crystallize in Space Group P-1 with Z = 8

A. Kálmán and Gy. Argay

Synopsis: Symmetry analysis of numerous triclinic structures retrieved from the Cambridge Structural Database with P-1 and Z = 8 revealed a rich variety of *2₁/*c pseudosymmetry, which may exist in the oblique unit cells. The migrations of these symmetries are accompanied by the irregular translations of their complementary operators, which may lead even to transitional space-group formations.

Acta Cryst. (1998). B54, 889-894    [doi:10.1107/S0108768198005448]

Structure of Ammonium Hydrogen Succinate at 80 and 20 K

S. Kashino, J. Taka, T. Yoshida, Y. Kubozono, H. Ishida and H. Maeda

Synopsis: The temperature dependence of the geometries of the hydrogen bonds before and after the second-order phase transition (T_c = 170 K) is studied. The OO distances of two O-HO hydrogen bonds involving the hydrogen succinate ions increase as the temperature decreases below T_c and the NO distance of a weak bifurcated hydrogen bond involving the ammonium ion decreases below T_c.

Acta Cryst. (1998). B54, 895-906    [doi:10.1107/S0108768198005515]

Structures and Photoreactivities of 2,4,6-Triisopropylbenzophenones

S. Fukushima, Y. Ito, H. Hosomi and S. Ohba

Synopsis: Crystal structures of eleven 2,4,6-triisopropylbenzophenones have been determined to show that the molecular structures are essentially the same, independent of the substituted groups. The photostability of 4^'-COOMe and 4^'-COCl derivatives in the solid state is attributed to the narrow reaction cavity around the triisopropylphenylcarbonyl moiety.

Acta Cryst. (1998). B54, 907-911    [doi:10.1107/S0108768198005503]

Crystal-to-Crystal Diastereoselective Transformation of 2,4,6-Triisopropyl-4'-(S)-phenylalaninocarbonylbenzophenone Methyl Ester

H. Hosomi, Y. Ito and S. Ohba

Synopsis: The diastereoselective photocyclization of the title compound was directly observed as a crystal-to-crystal transformation. The crystal structure after 100% conversion has been determined, revealing that the carbonyl C and the isopropyl central C atoms approach each other to form a C-C bond.

Acta Cryst. (1998). B54, 912-920    [doi:10.1107/S0108768198006545]

Charge Density Study of 2-Pyridone

H. W. Yang and B. M. Craven

Synopsis: Experimentally determined properties of 2-pyridone include the total electron density and its Laplacian, the electrostatic potential and the dipole moment. These are used to characterize the N-HO, C-HO and C-H interactions.

Acta Cryst. (1998). B54, 921-924    [doi:10.1107/S0108768198007381]

Arrays with Local Centers of Symmetry in Space Groups Pca2₁ and Pna2₁

R. E. Marsh, V. Schomaker and F. H. Herbstein

Synopsis: Nearly 200 examples of local centers of symmetry have been found in each of the space groups Pca2₁ and Pna2₁ for Z > 4. These are concentrated about x=1/8, y=1/4 and x=1/8, y=0, respectively. Implications for the refinement process are discussed.

short communications

Acta Cryst. (1998). B54, 925-926    [doi:10.1107/S0108768198007393]

Concerning the Phase of Al-Cr-Ni

R. E. Marsh

Synopsis: The original refinement of this structure, in space group P6₃, was restrained so as to yield a presumed composition of approximately Al₇₆Cr₁₈Ni₆. Revision of the space group, to P6₃/m, permits unrestrained refinement which indicates no more than a trace amount of Ni.

books received

Acta Cryst. (1998). B54, 927    [doi:10.1107/S0108768198011033]

X-ray charge densities and chemical bonding by P. Coppens

international union of crystallography

Acta Cryst. (1998). B54, 928-929    [doi:10.1107/S0108768198013706]

Prices of IUCr journals

Acta Cryst. (1998). B54, 931-936

Subject index to volume B54 (1998)

Acta Cryst. (1998). B54, 937-938

Formula index to volume B54 (1998)

Acta Cryst. (1998). B54, 939-943

Author index to volume B54 (1998)

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