Acta Crystallographica Section B

Structural Science

Volume 54, Part 5 (October 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

obituaries
research papers

obituaries

Acta Cryst. (1998). B54, 505-506 [doi:10.1107/S0108768198099893]

Kenneth Nyitray Trueblood

J. P. Glusker

research papers

Acta Cryst. (1998). B54, 507-514 [doi:10.1107/S0108768198003243]

Correlation of Internal Torsional Motion with Overall Molecular Motion in Crystals

V. Schomaker and K. N. Trueblood

Synopsis: A model is described for allowing for internal torsional motion and its correlation with overall molecular motion in crystals, in the quadratic approximation. Examples are given and limitations discussed.

Acta Cryst. (1998). B54, 515-523 [doi:10.1107/S0108768197018181]

Lattice-Dynamical Estimation of Atomic Displacement Parameters in Carbonates: Calcite and Aragonite CaCO₃, Dolomite CaMg(CO₃)₂ and Magnesite MgCO₃

T. Pilati, F. Demartin and C. M. Gramaccioli

Synopsis: Atomic displacement parameters, vibrational frequencies and estimates of specific heat and entropy have been evaluated for carbonates of the calcite group using lattice dynamics and empirical transferable force fields.

Acta Cryst. (1998). B54, 524-530 [doi:10.1107/S0108768197018466]

Superstructure Determination of PbZrO₃

K. Yamasaki, Y. Soejima and K. F. Fischer

Synopsis: The superstructure of PbZrO₃ is determined by using 0.35 Å synchrotron radiation with only the data of superlattice reflections. It is found that Zr atoms show the antiphase-type displacements along the z axis.

Acta Cryst. (1998). B54, 531-546 [doi:10.1107/S0108768197019927]

Cristobalite-Related Phases in the NaAlO₂-NaAlSiO₄ System. I. Two Tetragonal and Two Orthorhombic Structures

J. G. Thompson, R. L. Withers, A. Melnitchenko and S. R. Palethorpe

Synopsis: The crystal structures of five new cristobalite-related sodium aluminosilicates with four different structure types have been refined by the Rietveld method from X-ray powder diffraction data. Good starting models for two of the structures were obtained from analogous phases, while starting models for the other two with previously unreported structure types were derived using a modulation wave approach.

Acta Cryst. (1998). B54, 547-557 [doi:10.1107/S0108768197019939]

Cristobalite-Related Phases in the NaAlO₂-NaAlSiO₄ System. II. A Commensurately Modulated Cubic Structure

R. L. Withers, J. G. Thompson, A. Melnitchenko and S. R. Palethorpe

Synopsis: The crystal structure of a commensurately modulated cubic cristobalite-related sodium aluminosilicate structure has been modelled using a modulation wave approach and the model tested against X-ray powder diffraction data using the Rietveld method. The tetrahedral framework model and Na/vacancy ordering were derived from consideration of the dominant modulation waves and a pseudo-extinction condition observed in the diffraction data. This is the first cubic cristobalite-related superstructure phase reported and provides insight into the enigmatic high-temperature structure of cristobalite.

Acta Cryst. (1998). B54, 558-563 [doi:10.1107/S0108768198000548]

Structure of Gallobicchulite. A Combined EXAFS/Neutron Powder Diffraction Refinement

N. Binsted, S. E. Dann, M. J. Pack and M. T. Weller

Synopsis: A combined refinement of neutron powder diffraction and gallium K-edge EXAFS has permitted the complete structure elucidation of Ca₈(Ga₂SiO₆)₄(OH)₈

Acta Cryst. (1998). B54, 564-567 [doi:10.1107/S0108768198000974]

Calculation of Structural Parameters in Isostructural Series: the Kieserite Group

S. Aleksovska, V. M. Petrusevski and B. Soptrajanov

Synopsis: The structural parameters of kieserite family members are predicted on the basis of the size of both cation and anion. The agreement between calculated and refined parameters is good.

Acta Cryst. (1998). B54, 568-577 [doi:10.1107/S0108768198001062]

Mixed Alkali Systems: Structure and ²⁹Si MASNMR of Li₂Si₂O₅ and K₂Si₂O₅

B. H. W. S. de Jong, H. T. J. Supèr, A. L. Spek, N. Veldman, G. Nachtegaal and J. C. Fischer

Synopsis: The crystal structures and NMR spectra of K₂Si₂O₅ and Li₂Si₂O₅ have been determined and the effect of moisture on mixed alkali aqueous and silicate systems described.

Acta Cryst. (1998). B54, 578-584 [doi:10.1107/S0108768198001207]

Pressure-Induced Octahedron Strain in VF₃-Type Compounds

H. Sowa and H. Ahsbahs

Synopsis: At high pressure the anion arrangement in TiF₃ and FeF₃ is deformed similar to a sphere-packing deformation of the type 8/3/c2, while repulsive interactions between the cations result in a certain extent of octahedron strain.

Acta Cryst. (1998). B54, 585-599 [doi:10.1107/S0108768198001979]

A New Global Parameterization of Perovskite Structures

N. W. Thomas

Synopsis: A new framework is proposed for the quantitative description of perovskite structures. It can be used to predict starting models for structural refinements from the chemical composition.

Acta Cryst. (1998). B54, 600-612 [doi:10.1107/S0108768198002286]

Structure, Charge and Spin Density in Na₂Ni(CN)₄.3H₂O at 295 and 30 K

H. Ptasiewicz-Bak, I. Olovsson and G. J. McIntyre

Synopsis: The structure and charge density for Na₂Ni(CN)₄.3H₂O at 295 and 30 K, with hydrogen parameters at 30 K, have been determined from neutron data. Spin density was determined by polarized neutrons at 1.6 K.

Acta Cryst. (1998). B54, 613-625 [doi:10.1107/S0108768198002328]

Phase Transitions and Structures at 10, 92 and 293 K in Eight Trigonal Double Salts M^I[M^III(NH₃)₆](ClO₄)₂X₂

B. N. Figgis, A. N. Sobolev and P. A. Reynolds

Synopsis: A phase transition from a very simple R-3m to an equally simple twinned R-3 structure is observed in most cases, in which trigonal symmetry of the M^III site is preserved. Crystal properties are correlated with M^I and X ionic radii and M^III-N distances.

Acta Cryst. (1998). B54, 626-634 [doi:10.1107/S010876819800233X]

Disorder in the Crystal Structure of Cs₂HgCl₄ Studied by the Maximum Entropy Method

B. Bagautdinov, J. Luedecke, M. Schneider and S. van Smaalen

Synopsis: Like other A₂BX₄-type compounds, Cs₂HgCl₄ exhibits large-amplitude anharmonic displacements at room temperature (soft mode). The Maximum Entropy Method is used to determine the atomic displacements corresponding to the disorder at room temperature.

Acta Cryst. (1998). B54, 635-644 [doi:10.1107/S0108768198002985]

Investigation of the Cs_xRb_1-xTiOAsO₄ Series. I. Crystal Structure Analysis and Pseudo-symmetry

M. N. Womersley, P. A. Thomas and D. L. Corker

Synopsis: Crystal structures of five crystals in the Cs_2xRb_2-2xTi₂O₂As₂O₈ series are reported and discussed. The low-temperature behaviour of two members (x = 0.71 and x = 0.86) is reported and analysed together with the room-temperature pseudo-symmetry of all the structures.

Acta Cryst. (1998). B54, 645-651 [doi:10.1107/S0108768198002997]

Investigation of the Cs_xRb_1-xTiOAsO₄ Series. II. The Problems of Interpretation of Residual Electron Densities in a Polar Space Group

P. A. Thomas and M. N. Womersley

Synopsis: The problems of refinements of structures in a polar space group, such as Pna2₁, are illustrated using the example of Cs_2xRb_2-2xTi₂O₂As₂O₈. Using a combination of simulated data sets and different refinement strategies, distinction between pseudo-symmetic `ghosting' and real atomic occupancy of inversion-related sites is made with the conclusion that some structures in the series are truly disordered.

Acta Cryst. (1998). B54, 652-656 [doi:10.1107/S0108768198004649]

Structure and Non-linear Optical Properties of -Barium Borate

D. F. Xue and S. Y. Zhang

Synopsis: The crystal structure and non-linear optical properties of [beta] -barium borate are theoretically investigated, from the chemical bond viewpoint.

Acta Cryst. (1998). B54, 657-662 [doi:10.1107/S0108768197020107]

An Unusual Hydrogen-Bonded Network Associated with Metal-Organic Chains: Structure and Crystal Packing of the Coordination Polymer [Cd(terephthalate)(H₂O)₃].4H₂O

O. A. Michaelides, D. Tsaousis, S. Skoulika, C. P. Raptopoulou and A. Terzis

Synopsis: The title compound is a polymer with metal-organic chains stacked along the a axis of the crystal. The structure is stabilized by an extensive hydrogen-bonded network comprising tridymite-like O₈ cages.

Acta Cryst. (1998). B54, 663-670 [doi:10.1107/S0108768198000536]

A Reversible Non-disruptive Phase Transition Shown by the Zinc Iodide Dimethylformamide Complex ZnI₂(dmf)₂

R. A. Edwards, A. J. Easteal, O. P. Gladkikh, W. T. Robinson, M. M. Turnbull and C. J. Wilkins

Synopsis: ZnI₂(dmf)₂, zinc diiodide bis(dimethylformamide), shows a reversible non-disruptive phase change at 228 K. The space group changes from C2/c to P2₁/n, with two new conformationally different molecules arising at low temperature from rotation of one of the dmf ligands through angles of either +25 or -43°. Application of differential scanning calorimetry gives [Delta] H = 1.44 kJ mol^-1.

Acta Cryst. (1998). B54, 671-676 [doi:10.1107/S0108768197015760]

2-Phenyl-4-hydroxyphthalazin-1-one: A Benzoannelated Derivative of Maleic Hydrazide

D. Becker, M. Botoshansky, N. Gasper, F. H. Herbstein and M. Karni

Synopsis: The crystal structure of C₁₄H₁₀N₂O₂ has been determined at 293 K and the hydrogen-bonding pattern compared with those in the related crystals maleic hydrazide (two polymorphs), dichloromaleic hydrazide and luminol. The measured dimensions of monoclinic maleic hydrazide have been compared with those obtained from an extensive series of high-level molecular orbital calculations.

Acta Cryst. (1998). B54, 677-686 [doi:10.1107/S0108768198000949]

More Space-Group Corrections: From Triclinic to Centred Monoclinic and to Rhombohedral; Also From P1 to P-1 and From Cc to C2/c

F. H. Herbstein and R. E. Marsh

Synopsis: Symmetry reported as lower than correct has been detected in (most of) the crystals discussed by using reduced cells and Niggli matrices.

Acta Cryst. (1998). B54, 687-694 [doi:10.1107/S0108768198000081]

Structure of the Tannin Geraniin Based on Conventional X-ray Data at 295 K and on Synchrotron Data at 293 and 120 K

P. Luger, M. Weber, S. Kashino, Y. Amakura, T. Yoshida, T. Okuda, G. Beurskens and Z. Dauter

Synopsis: The 75 non-H atom structure of geraniin heptahydrate, a tannin with antidiarrheic activity, was solved using a 20-atom fragment in an initial vector search with DIRDIF. Low-temperature synchrotron data allowed identification of almost all the H atoms, so that ~30 different hydrogen bonds can be studied.

Acta Cryst. (1998). B54, 695-704 [doi:10.1107/S0108768198003231]

Supramolecular Alcohol-Amine Crystals and Their Hydrogen-Bond Patterns

J. H. Loehlin, K. J. Franz, L. Gist and R. H. Moore

Synopsis: Five p-phenylenediamine-alcohol cocrystal structures and the graph-set analysis of the hydrogen-bonding patterns in published alcohol-amine structures are discussed.