Acta Crystallographica Section B

Structural Science

Volume 52, Part 4 (August 1996)

Cover illustration: Molecular structure and packing of 7-dispiro[2.0.2.1]heptane carboxylic acid. Courtesy of D. S. Yufit, P. R. Mallinson, K. W. Muir, S. I. Kozhushkov and A. De Meijere.

• research papers

research papers

Acta Cryst. (1996). B52, 569-575    [doi:10.1107/S0108768196000250]

A synchrotron X-ray study of the electron density in Y₂BaCuO₅

R. Hsu, E. N. Maslen and N. Ishizawa

Synopsis: The features in a synchrotron radiation image for Y₂BaCuO₅ are predominantly due to exchange depletion of the electron density between second nearest-neighbour cations.

Acta Cryst. (1996). B52, 576-579    [doi:10.1107/S0108768196003084]

Synchrotron X-ray electron density in the layered LaOCl structure

E. N. Maslen, V. A. Streltsov, N. R. Streltsova and N. Ishizawa

Synopsis: The deformation electron density in LaOCl measured with synchrotron X-radiation accumulates in the inter-layer region stabilizing the structure that contains layers of positively charged Cl atoms.

Acta Cryst. (1996). B52, 580-585    [doi:10.1107/S0108768196000481]

Structure of Ce₂Pt₆Ga₁₅: interplanar disorder from the Ce₂Ga₃ layers

G. H. Kwei, A. C. Lawson, A. C. Larson, B. Morosin, E. M. Larson and P. C. Canfield

Synopsis: The structure of the heavy fermion compound Ce₂Pt₆Ga₁₅ has been determined from neutron powder and X-ray/neutron single-crystal diffraction. The structure is unusual in that Ce layers have 1/3 of the Ce atoms replaced by groups of three Ga atoms. Weak diffuse scattering suggests that disorder arises from a lack of registration of successive Ce₂Ga₃ layers.

Acta Cryst. (1996). B52, 586-595    [doi:10.1107/S0108768196002686]

Ab initio Hartree-Fock study of the electronic charge density of the cubic boron nitride and its comparison with experiments

A. Lichanot, P. Azavant and U. Pietsch

Synopsis: The electronic charge density of cubic BN and structure factors are calculated at the ab initio Hartree-Fock level. It reveals the semi-covalent character of the BN bond and a charge transfer from B to N close to unity. Comparison with experiments leads to a satisfactory agreement.

Acta Cryst. (1996). B52, 596-604    [doi:10.1107/S0108768196003576]

A critical review of the experimental valence charge density of GaAs

U. Pietsch and N. K. Hansen

Synopsis: The valence charge and difference densities of GaAs were calculated without foregoing refinements of a charge density model using six different data sets published until now. Only four of these describe the covalent bond as well as the partial charge transfer between neighboring atoms in qualitative agreement with the theoretical prediction.

Acta Cryst. (1996). B52, 605-609    [doi:10.1107/S0108768196003400]

Kristallstruktur und zwillingsbildung der intermetallischen phase -Bi₂Rh

M. Ruck

Synopsis: A new triclinic structure type adopted by the high-temperature polymorph of an intermetallic phase was prepared.

Acta Cryst. (1996). B52, 610-615    [doi:10.1107/S0108768196003813]

Antiferroelectric modulations in Sb₂WO₆ and Sb₂MoO₆

C. D. Ling, R. L. Withers, A. D. Rae, S. Schmid and J. G. Thompson

Synopsis: The structure of Sb₂WO₆, previously reported in the space group P1, is re-refined in P-1 as a 2a x 2b x 2c superstructure, improving the residual R from 0.12 to 0.04. Synthesis of the isostructural phase Sb₂MoO₆ is also reported.

Acta Cryst. (1996). B52, 616-627    [doi:10.1107/S0108768196004132]

Sodalite, Na₄Si₃Al₃O₁₂Cl: structure and ionic mobility at high temperatures by neutron diffraction

R. K. McMullan, S. Ghose, N. Haga and V. Schomaker

Synopsis: Refinement of the high-temperature structures of sodalite (295-1200 K) based on single-crystal neutron diffraction and an anharmonic thermal vibration model for Na⁺, Cl^- and O indicate (i) the thermal expansion from an untwisting of the aluminosilicate framework due to increasing translational motions of Na⁺ coupled with librations of SiO₄/AlO₄ tetrahedra and (ii) Na⁺-Cl^- diffusion along <111> channels.

Acta Cryst. (1996). B52, 628-642    [doi:10.1107/S0108768196004673]

Static disorder in the incommensurate structure of the high T_c superconductor Bi₂Sr₂CaCu₂O₈₊

D. Grebille, H. Leligny, A. Ruyter, Ph. Labbé and B. Raveau

Synopsis: The incommensurate modulated structure of the high T_c superconductor Bi₂Sr₂CaCu₂O₈₊ has been explained on the basis of a disorder of the Bi atom.

Acta Cryst. (1996). B52, 643-650    [doi:10.1107/S0108768195016089]

Structure of the polytypic -form of P₃N₃(OCH₂CF₂CF₂CH₂O)F₄

Z. Wang, R. D. Willett, A. J. Elias, R. L. Kirchmeier and J. M. Shreeve

Synopsis: The structure of the polytypic form of the title compound can be described in terms of a layer structure which contains an ABAABA repeat pattern of layers. The A and B layers have pseudoslab symmetries pc2a and p2₁/c11, respectively.

Acta Cryst. (1996). B52, 651-661    [doi:10.1107/S0108768195016302]

Structural studies on monofluorinated derivatives of the phytohormone indole-3-acetic acid (auxin)

A. Antolic, B. Kojic-Prodic, S. Tomic, B. Nigovic, V. Magnus and J. D. Cohen

Synopsis: s part of the molecular recognition studies on auxins, a series of indole-3-acetic acids fluorinated at the phenyl ring positions 4, 5, 6 and 7 has been examined. Structural studies based on X-ray structure analysis, computational chemistry methods and some physico-chemical properties are presented and correlated with bioassays performed on the Avena and Pisum sativum.

Acta Cryst. (1996). B52, 662-667    [doi:10.1107/S010876819600047X]

Experimental and theoretical morphologies of diuron, N'-(3,4-dichlorophenyl)-N,N-dimethylurea

G. Pfefer and R. Boistelle

Synopsis: The experimental morphology of diuron crystals, a weed killer, is compared with the theoretical morphology determined using both a geometrical observation law and molecular mechanics calculations.

Acta Cryst. (1996). B52, 668-676    [doi:10.1107/S010876819600105X]

Experimental charge density study of 7-dispiro[2.0.2.1]heptane carboxylic acid

D. S. Yufit, P. R. Mallinson, K. W. Muir, S. I. Kozhushkov and A. De Meijere

Synopsis: The effect of substitution on the bonding in the polyspirocyclopropane frame and chemical behaviour of the title compound is discussed in terms of the topological analysis of experimental multipole charge density distributions.

Acta Cryst. (1996). B52, 677-684    [doi:10.1107/S0108768196003035]

Statistical analysis of noncovalent interactions of anion groups in crystal structures. I. Hydrogen bonding of sulfate anions

L. Chertanova and C. Pascard

Synopsis: The high capacity of the sulfate dianion to form multiple hydrogen bonds has been analyzed, using the Cambridge Structural Database.

Acta Cryst. (1996). B52, 685-690    [doi:10.1107/S0108768196003011]

Statistical analysis of noncovalent interactions of anion groups in crystal structures. II. Hydrogen bonding of thiocyanate anions

L. Tchertanov and C. Pascard

Synopsis: The first systematic analysis of the hydrogen-bonding properties of the (SCN)^- anion was performed. The bidentate acceptor function of thiocyanate was observed.

Acta Cryst. (1996). B52, 691-696    [doi:10.1107/S0108768196003023]

Neutron diffraction of a complex of 1,8-bis(dimethylamino)naphthalene with 1,2-dichloromaleic acid

K. Wozniak, C. C. Wilson, K. S. Knight, W. Jones and E. Grech

Synopsis: Neutron single-crystal data of a complex of 1,8-bis(dimethylamino)naphthalene with 1,2-dichloromaleic acid were collected at 100 K at ISIS and have been compared with single crystal data from X-ray diffraction.

Acta Cryst. (1996). B52, 697-706    [doi:10.1107/S0108768196003187]

Structural, kinetic and thermodynamic aspects of the conformational dimorphism of diethyl 3,6-dibromo-2,5-dihydroxyterephthalate

C. Näther, N. Nagel, H. Bock, W. Seitz and Z. Havlas

Synopsis: The crystal structures of diethyl 3,6-dibromo-2,5-dihydroxyterephthalate have been determined and the structural, kinetic and thermodynamic aspects of the conformational dimorphism in the title compound investigated.

Acta Cryst. (1996). B52, 707-712    [doi:10.1107/S0108768196003461]

Simple averaging procedure for aromatic ring system: mean molecular fragment of tryptophan metabolites

A. Wakahara and T. Ishida

Synopsis: A simple averaging procedure for bond lengths and angles applicable to an aromatic ring system was applied to the crystal structures of tryptophan metabolites, and mean values for the indole ring were proposed.

Acta Cryst. (1996). B52, 713-719    [doi:10.1107/S0108768196000201]

Planarity of nitro-substituted phenothiazines

C. P. Brock, P. J. DeLaLuz, M. Golinski, M. A. Lloyd, T. C. Vanaman and D. S. Watt

Synopsis: The structures of three 2- and 3-nitrophenothiazine derivatives, which are all bright red, have been determined. One of them forms stacks in which donor and acceptor regions of the almost planar ring system alternate.

Acta Cryst. (1996). B52, 720-727    [doi:10.1107/S0108768196003977]

A database study of the bonding and conformation of bis-sulfonylamide/-imide moieties

P. Bombicz, M. Czugler, A. Kálmán and I. Kapovits

Synopsis: Analysis of 44 structures containing R-SO₂-NQ-SO₂-R^' (Q = e^-, H, alkyl, aryl, O or S; R, R^' = Me, Et or Ph) units retrieved from the Cambridge Structural Database reveals marked differences between the archetypes of the S-N bonds (i.e. nitrogen charged or neutral) in the range 1.57-1.76 Å. The S^VI-X bonds of the type S^VI[O,O^',N,C] tetrahedra are characterized and correlated with the bond angles and torsion angles formed around the S atoms. It is shown that the interdependence of the S-X bonds and their interbond angles is principally governed by the environment of the N atoms.

Acta Cryst. (1996). B52, 728-733    [doi:10.1107/S0108768196004569]

Structures of three inclusion compounds of cholanamide with either (S)-enantiomer, (R)-enantiomer or an optically resolved mixture of butan-2-ol

P. Briozzo, T. Kondo, K. Sada, M. Miyata and K. Miki

Synopsis: Crystal structures of three inclusion compounds of cholanamide obtained from the solutions of (S)-butan-2-ol, (R)-butan-2-ol and racemic butan-2-ol have been determined. The host cholanamide molecules form the same layered arrangements providing channel spaces for the guest butan-2-ol molecules, where the pure (S)-and (R)-enantiomers of butan-2-ol and the (S)-enriched mixture of enantiomers are accommodated, respectively.

Acta Cryst. (1996). B52, 734-745    [doi:10.1107/S0108768196005319]

The hydrogen-bond C-H donor and -acceptor characteristics of three-membered rings

F. H. Allen, J. P. M. Lommerse, V. J. Hoy, J. A. K. Howard and G. R. Desiraju

Synopsis: Three-membered ring C-H donors are shown to form hydrogen bonds to oxygen acceptors that are of similar strength to Csp²-HO bonds. The existence of O,N-H(ring) bonding, predicted from spectroscopic results, is confirmed by analysis of the available crystallographic data.

Acta Cryst. (1996). B52, 746-752    [doi:10.1107/S0108768196005204]

Tautomerism in 3{5}-(dimethoxyphenyl)pyrazoles

M. A. Halcrow, H. R. Powell and M. J. Duer

Synopsis: The single crystal structure of 3{5}-(2^',5^'-dimethoxyphenyl)pyrazole contains purely the 5-substituted tautomer, while 3{5}-(3^',4^'-dimethoxyphenyl)pyrazole crystallizes as a prototropically disordered hemihydrate. These observations are supported by solid-state and solution NMR measurements.

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