Structural Science

 

Acta Cryst. (1999). B55, 1-7  [ doi:10.1107/S0108768198005400 ]

Synchrotron X-ray study of the electron density in RFeO₃ (R = Nd, Dy)

V. A. Streltsov and N. Ishizawa

Synopsis: Synchrotron X-ray diffraction images of the deformation electron density () for two rare-earth orthoferrites RFeO₃ (R = Nd, Dy) show a high degree of correlation between aspherical electron densities around magnetic R and Fe atoms in each compound, which can be related to the magnetic properties of these orthoferrites.

Online February 1999

 

Acta Cryst. (1999). B55, 8-16  [ doi:10.1107/S0108768198005758 ]

Temperature-dependent neutron powder diffraction evidence for splitting of the cationic sites in ferroelectric PbHf_0.4Ti_0.6O₃

C. Muller, J.-L. Baudour, V. Madigou, F. Bouree, J.-M. Kiat, C. Favotto and M. Roubin

Synopsis: The ferroelectric-to-paraelectric phase transition in the lead hafnate titanate PbHf_0.4Ti_0.6O₃ has been studied by temperature-dependent neutron powder diffraction. Particular attention has been directed towards the splitting of the Hf/Ti cationic site and the distortion of the oxygen octahedra.

Online February 1999

 

Acta Cryst. (1999). B55, 17-23  [ doi:10.1107/S010876819800737X ]

Neutron structures of ammonium tetrafluoroberyllate

R. C. Srivastava, W. T. Klooster and T. F. Koetzle

Synopsis: Neutron structures of ammonium tetrafluoroberyllate at 200, 163 and 20  K reveal that both the BeF and the NH ions rotate and shift positions upon going from the paraelectric to the ferroelectric phase, resulting in stronger hydrogen-bonding interactions in the ferroelectric phase accompanied by a doubling of the crystallographic a axis.

Online February 1999

 

Acta Cryst. (1999). B55, 24-30  [ doi:10.1107/S010876819800963X ]

High-temperature phases of NaNbO₃ and NaTaO₃

C. N. W. Darlington and K. S. Knight

Synopsis: Diffraction patterns of the high-temperature phases of the perovskites sodium niobate and sodium tantalate have been collected at intervals of 5  K using the high-resolution powder diffractometer HRPD at the ISIS neutron spallation source. This has allowed the structural changes with temperature within a single phase to be determined for the first time.

Online February 1999

 

Acta Cryst. (1999). B55, 31-34  [ doi:10.1107/S0108768198009860 ]

Residual short-range order in the heavy fermion compound CeInCu₂

I. Takahashi, A. Kagayama, G. Oomi, Y. Onuki and T. Komatsubara

Synopsis: From the analysis of X-ray diffuse scattering, short-range order is indicated in CeInCu₂. A superstructure-like disorder between Ce and In atoms is clarified; the feature is probably related to the fact that the structural disorder hardly affects the residual resistivity at low temperature.

Online February 1999

 

Acta Cryst. (1999). B55, 35-44  [ doi:10.1107/S0108768198007009 ]

Disorder determined by high-resolution powder diffraction: structure of pentamethylcyclopentadienyllithium

R. E. Dinnebier, M. Schneider, S. van Smaalen, F. Olbrich and U. Behrens

Synopsis: Modelling and calculations by the maximum entropy method (MEM) have been used to solve the crystal structure of pentamethylcyclopentadienyllithium (LiCp*) from a high-resolution powder pattern. The structure was found to comprise polymeric `multidecker' chains. The pentamethylcyclopentadienyl anions are coplanar with each other and show threefold disorder.

Online February 1999

 

Acta Cryst. (1999). B55, 45-54  [ doi:10.1107/S0108768198005746 ]

Electron density study of urea using TDS-corrected X-ray diffraction data: quantitative comparison of experimental and theoretical results

V. Zavodnik, A. Stash, V. Tsirelson, R. de Vries and D. Feil

Synopsis: The electron-density distribution in urea obtained by X-ray diffraction is compared quantitatively in direct and reciprocal space with the outcome of Hartree-Fock and density-functional solid-state calculations with different correlation and exchange potentials.

Online February 1999

 

Acta Cryst. (1999). B55, 55-69  [ doi:10.1107/S0108768198006557 ]

Crystal and molecular structures of diazapyrenes and a study of interactions

R. Kiralj, B. Kojic-Prodic, I. Piantanida and M. Zinic

Synopsis: The crystal structures of 5,10-dimethyl-4,9-diazapyrene and the new compound 2,7-dimethyl-4,9-diazapyrene are presented and the experimental bond lengths are compared with those calculated by molecular mechanics and semi-empirical methods and values predicted by valence-bond and variable-electronegativity self-consistent field (VESCF) methods. The quantitative parameters of interactions have been calculated for two diazapyrenes and other pyrene-like molecules selected from the Cambridge Structural Database and used for classification of their crystal-packing types; the analysis is based on geometrical parameters and elements of electronic structure.

Online February 1999

 

Acta Cryst. (1999). B55, 70-77  [ doi:10.1107/S0108768198006570 ]

Low-temperature crystallization and structure determination of N-(trifluoromethyl)formamide, N-(2,2,2-trifluoroethyl)formamide and 2,2,2-trifluoroethyl isocyanide

G. J. Perpétuo, J. Buschmann, P. Luger, D. Lentz and D. Dreissig

Synopsis: The in situ crystallization and structure determination of the three title compounds is presented. The molecular geometries are in each case compared with the results of ab initio studies.

Online February 1999

 

Acta Cryst. (1999). B55, 78-84  [ doi:10.1107/S0108768198007848 ]

Experimental charge density and electrostatic potential in nicotinamide

Y. Miwa, T. Mizuno, K. Tsuchida, T. Taga and Y. Iwata

Synopsis: The accurate crystal structure of nicotinamide was determined from X-ray and neutron diffraction experiments. The electron distribution determined by the maximum entropy method indicates that the electrostatic properties depend on the rotation of the carboxamide group out of the pyridine plane.

Online February 1999

 

Acta Cryst. (1999). B55, 85-94  [ doi:10.1107/S0108768198008945 ]

Structures of 2,6-disubstituted naphthalenes

J. A. Kaduk and J. T. Golab

Synopsis: The crystal structures of 2,6-naphthalenedicarboxylic acid and dimethyl 2,6-naphthalenedicarboxylate have been solved an initio, and refined (along with that of their precursor, 2,6-dimethylnaphthalene) using powder diffraction data.

Online February 1999

 

Acta Cryst. (1999). B55, 95-103  [ doi:10.1107/S0108768198009252 ]

Three conformational polymorphs and order-disorder phase transition in a calix[4]arene bis(crown)

P. Thuéry, M. Nierlich, R. Calemczuk, M. Saadioui, Z. Asfari and J. Vicens

Synopsis: Three polymorphic modifications of a calix[4]arene bis(crown) including an azobenzene unit have been structurally characterized. The phase transition between two of them was investigated by X-ray diffraction and adiabatic calorimetry.

Online February 1999

 

Acta Cryst. (1999). B55, 104-113  [ doi:10.1107/S0108768198010192 ]

Symmetry, pseudosymmetry and packing disorder in the alcohol solvates of L-leucyl-L-valine

C. H. Görbitz and E. Torgersen

Synopsis: L-Leu-L-Val forms non-isomorphous 1:1 solvates with methanol, ethanol (LVE) and 2-propanol (LV2P). LVE has four peptide molecules in the asymmetric unit, with intricate pseudosymmetry. LV2P retains the same hydrogen-bonding pattern as LVE with only half the unit-cell volume. This is owing to packing disorder resulting from four alternative peptide conformations.

Online February 1999

 

Acta Cryst. (1999). B55, 114-122  [ doi:10.1107/S0108768198009392 ]

Structure of mono-acid even-numbered -triacylglycerols

A. van Langevelde, K. van Malssen, F. Hollander, R. Peschar and H. Schenk

Synopsis: The crystal structure of tripalmitin (PPP), a C_nC_nC_n-type (n = even) triacylglycerol (TAG), was determined and used to build an overlap model for this type of TAG. From the model the crystal structures of the unknown members of this series are predicted.

Online February 1999

 

Acta Cryst. (1999). B55, 123-130  [ doi:10.1107/S0108768198009872 ]

3,4:9,10-Perylenetetracarboxylic dianhydride (PTCDA) by electron crystallography

T. Ogawa, K. Kuwamoto, S. Isoda, T. Kobayashi and N. Karl

Synopsis: The crystal structures of the and modifications of PTCDA were analyzed as projected structures on the (102) planes by electron crystallography using an imaging plate.

Online February 1999

 

Acta Cryst. (1999). B55, 131  [ doi:10.1107/S010876819801427X ]

Theoretical prediction of bond-valence networks. II. Comparison of the graph-matrix and resonance-bond approaches. Erratum

J. S. Rutherford

Synopsis: The correct version of Fig. 2 in the paper by Rutherford [Acta Cryst. (1998), B54, 204-210] is given.

Online February 1999

 

Acta Cryst. (1999). B55, 132-138  [ doi:10.1107/S0108768198015420 ]

Notes for Authors 1999

Online February 1999