Acta Crystallographica Section B

Structural Science

Volume 53, Part 6 (December 1997)

Cover illustration: Contoured distribution of hydrogen bonds from N-H and O-H donors about the oxygen acceptors of the disulfate dianion. Data for the 232 hydrogen bonds (O...H > 2.62 Å) were computed from the Cambridge Structural Database and the required symmetry was applied to generate the final distribution. Courtesy of M. Verdonk and J. Cole

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

research papers

Acta Cryst. (1997). B53, 851-860    [doi:10.1107/S0108768197006186]

Re-Refinement of Composite Modulated Nb₂Zr_x-2O_2x+1 (x = 8) Using Synchrotron Radiation Data

S. Schmid, J. G. Thompson, R. L. Withers, V. Petrícek, N. Ishizawa and S. Kishimoto

Synopsis: The structure refinement of composite modulated Nb₂Zr_x-2O_2x+1 (x = 8) has been carried out in superspace group Amma(10)0s0. The equivalence of this present result to an earlier published refinement of the x = 12 member is established.

Acta Cryst. (1997). B53, 861-869    [doi:10.1107/S0108768197007787]

Structure Refinements of the Layered Intergrowth Phases Sb^IIISb^{V x}A_1-xTiO₆ (x0, A = Ta, Nb) Using Synchrotron X-ray Powder Diffraction Data

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

Synopsis: The structures of the layered intergrowth phases Sb^IIISb_x^VA_1-xTiO₆ (x0, A = Ta, Nb) have been refined by the Rietveld method, using synchrotron X-ray diffraction data. Starting models were proposed on the basis that the phases represented n = 1 in the series Sb_n^IIISb_x^VA_n-xTiO_4n+2, for which the n = 3 structures (x = 1.26, A = Ta and x = 0.89, A = Nb) had been previously solved by single crystal X-ray diffraction. The models were found to be essentially correct.

Acta Cryst. (1997). B53, 870-879    [doi:10.1107/S0108768197007817]

Electron Density Distribution in LiB₃O₅ at 293 K

C. Le Hénaff, N. K. Hansen, J. Protas and G. Marnier

Synopsis: The - bonding is analysed using the Hansen-Coppens multipole model and compared with Hartree-Fock calculations. The amount of transfer of electrons from the O atoms to the triangularly coordinated B atoms is specified.

Acta Cryst. (1997). B53, 880-884    [doi:10.1107/S0108768197008094]

Neutron Diffraction Study of the Ambient-Pressure, Rutile-Type and the High-Pressure, CaCl₂-Type Phases of Ruthenium Dioxide

J. Haines, J. M. Léger, O. Schulte and S. Hull

Synopsis: Compression of the RuO₆ octahedron is anisotropic. In the high-pressure phase the octahedra are rotated by 1.1° with respect to the ambient-pressure phase.

Acta Cryst. (1997). B53, 885-894    [doi:10.1107/S0108768197008240]

New Bond-Valence Sum Model

J. P. Naskar, S. Hati and D. Datta

Synopsis: A new model is proposed to accommodate zero and some negative oxidation states of a central atom in the bond-valence sum formalism.

Acta Cryst. (1997). B53, 895-903    [doi:10.1107/S0108768197008331]

Three New Polymorphic Forms of Molybdenum Pentachloride

J. Beck and F. Wolf

Synopsis: Three new polymorphic modifications of MoCl₅ have been obtained as single crystals by solvothermal syntheses using CCl₄ and SbCl₅ as solvents. All structures consist of double octahedral Mo₂Cl₁₀ molecules and are derived from the closest packings of Cl atoms with different stacking sequences.

Acta Cryst. (1997). B53, 904-915    [doi:10.1107/S0108768197008549]

Statistical Analysis of Noncovalent Interactions of Anion Groups in Crystal Structures. III. Metal Complexes of Thiocyanate and their Hydrogen-Donor Accepting Function

L. Tchertanov and C. Pascard

Synopsis: The bidentate function of the thiocyanate anion with respect to metals and/or hydrogen-donor groups was systematically studied using the Cambridge Structural Database.

Acta Cryst. (1997). B53, 916-922    [doi:10.1107/S0108768197010422]

Multi-Solution Genetic Algorithm Approach to Surface Structure Determination Using Direct Methods

E. Landree, C. Collazo-Davila and L. D. Marks

Synopsis: Models of two-dimensional centrosymmetric and non- centrosymmetric structures have been generated and used to test genetic algorithms for direct phasing of surface diffraction data.

Acta Cryst. (1997). B53, 923-927    [doi:10.1107/S0108768197005429]

Structure and Motion of Tetrakis(trichlorophosphazeno)phosphonium Hexachlorophosphate, [P(NPCl₃)₄]⁺PCl₆^-, at 93 K

F. Belaj

Synopsis: The crystal structure of [P(NPCl₃)₄]⁺PCl₆^-, determined at 93 K, and the thermal motion of the highly flexible cation, analysed in terms of the rigid-body model with allowances for intramolecular torsions, are reported.

Acta Cryst. (1997). B53, 928-938    [doi:10.1107/S0108768197005132]

Rigid-Body Disorder Models for the High-Temperature Phase of Ferrocene

C. P. Brock and Y. Fu

Synopsis: The 164 K phase transition of ferrocene is not a simple order-disorder transition.

Acta Cryst. (1997). B53, 939-944    [doi:10.1107/S0108768197007830]

Phase Transitions in Tris(3,5-dimethylpyrazol-1-yl)methane. The Structure of the High-Temperature Phase from X-ray Powder Diffraction

L. E. Ochando, J. Rius, D. Louër, R. M. Claramunt, C. Lopez, J. Elguero and J. M. Amigó

Synopsis: The effectiveness of the Patterson search method has been demonstrated by determining the crystal structure of the high-temperature phase of C₁₆H₂₂N₆ from laboratory X-ray powder diffraction data. Phase transitions between two isomers of the title compound have been investigated.

Acta Cryst. (1997). B53, 945-952    [doi:10.1107/S0108768197008033]

Crystallographic and Molecular Mechanics Study of Imidooxy Anticonvulsants

M. Ciechanowicz-Rutkowska, H. F. Lieberman, M. B. Hursthouse and K. R. Scott

Synopsis: The results of conformational analysis of seven imidooxy derivatives and the molecular structures found in the crystal for five of them are reported and examined in relation to their activity as anticonvulsants.

Acta Cryst. (1997). B53, 953-960    [doi:10.1107/S0108768197008343]

Structures of the Phosphazenes [ClC(NPCl₃)₂]⁺PCl₆^- and [CH₃C(NPCl₃)₂]⁺SbCl₆^- at 90 K

F. Belaj

Synopsis: The first crystal structures of compounds in which two NPCl₃ groups are bonded to a single C atom are reported. The cations show the same cis-trans conformations of the backbone; the extremely flexible C-N-P angles can be attributed to intramolecular contacts.

Acta Cryst. (1997). B53, 961-967    [doi:10.1107/S0108768197008562]

Diethyl 2-Benzimidazol-1-ylsuccinate-Picric Acid (1/1) - An Inclusion Molecular Complex

P. Zaderenko, M. S. Gil, P. López, P. Ballesteros, I. Fonseca and A. Albert

Synopsis: The crystal structure of diethyl 2-benzimidazol-1-ylsuccinate-picric acid (1/1) has been determined by X-ray diffraction analysis. The benzimidazole moiety of the molecules forms channels along the a axis in which the picric acid molecules are located, forming an inclusion molecular complex.

Acta Cryst. (1997). B53, 968-975    [doi:10.1107/S0108768197008665]

Recognizing the (False Symmetry) Triclinic (aP) to (True Symmetry) Centred Monoclinic (mC) Pathology

F. H. Herbstein

Synopsis: Examination of the published data for about fifty crystals where the originally reported triclinic unit cell has been corrected to centred monoclinic re-affirms the importance of calculating the Niggli matrix (metric tensor) as early as possible in a crystal structure analysis.

Acta Cryst. (1997). B53, 976-983    [doi:10.1107/S0108768197009142]

Structure and Serotonin 5-HT_2C Receptor Activity of ortho- and meta-Substituted Phenylpiperazines

M. L. Verdonk, J. W. Voogd, J. A. Kanters, J. Kroon, R. den Besten, L. Brandsma, D. Leysen and J. Kelder

Synopsis: X-ray diffraction and molecular mechanics calculations are used to determine the 5-HT_2C receptor activating conformation of phenylpiperazines. The conclusions are supported by preliminary biological studies on two novel 5-HT_2C ligands.

Acta Cryst. (1997). B53, 984-995    [doi:10.1107/S010876819700918X]

Packing Modes in Nitrobenzene Derivatives. I. The Single Stacks

I. André, C. Foces-Foces, F. H. Cano and M. Martinez-Ripoll

Synopsis: Crystal packing modes of nitrobenzene derivatives are pre- sented. The different types of `single stack' modes are described in terms of geometrical parameters.

Acta Cryst. (1997). B53, 996-1005    [doi:10.1107/S0108768197010835]

Packing Modes in Nitrobenzene Derivatives. II. The `Pseudo-Herringbone' Mode

I. André, C. Foces-Foces, F. H. Cano and M. Martinez-Ripoll

Synopsis: The `pseudo-herringbone' mode of packing for nitrobenzene derivatives is analysed. The mode is divided into four motifs, according to geometrical parameters.

Acta Cryst. (1997). B53, 1006-1016    [doi:10.1107/S0108768197010227]

HalogenO(Nitro) Supramolecular Synthon in Crystal Engineering: A Combined Crystallographic Database and Ab Initio Molecular Orbital Study

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

Synopsis: Analysis of crystallographic data indicates that C-XO(nitro) interactions increase in strength in the order Cl > Br > I, and that the frequency of formation of `bifurcated' motifs, involving X approach between the nitro-O atoms, increases in the same order. Intermolecular pertubation theory calculations on ClO and BrO interactions agree with these geometrical observations and yield a ClO interaction energy of ca -6 kJ mol^-1 at the 6-31G^* basis set level.

Acta Cryst. (1997). B53, 1017-1024    [doi:10.1107/S0108768197010239]

Hydrogen-Bond Acceptor Properties of Nitro-O Atoms: A Combined Crystallographic Database and Ab Initio Molecular Orbital Study

F. H. Allen, C. A. Baalham, J. P. M. Lommerse, P. R. Raithby and E. Sparr

Synopsis: Analysis of crystallographic data shows that nitro-OH-N,O hydrogen bonds are significantly longer (weaker) than their counterparts that involve >C=O acceptors and prefer to form asymmetric motifs with respect to the nitro-O atoms. Intermolecular perturbation theory calculations agree with these experimental observations and indicate a hydrogen-bond energy of -15 kJ mol^-1 at the 6-31G^** basis set level.

short communications

Acta Cryst. (1997). B53, 1025    [doi:10.1107/S0108768197099588]

Disorder in cyclodextrin clathrates: X-ray diffuse scattering analysis of -cyclodextrin cyclopentanone hydrate. Erratum

G. Le Bas and J. Doucet

Synopsis: Correction to Acta Cryst. (1997). B53, 673-679.

Acta Cryst. (1997). B53, 1026    [doi:10.1107/S0108768197099576]

Structures and magnetic properties of dimeric copper(II) benzoylformates. Erratum

A. Harada, M. Tsuchimoto, S. Ohba, K. Iwasawa and T. Tokii

Synopsis: Correction to Acta Cryst. (1997). B53, 654-661.

books received

Acta Cryst. (1997). B53, 1027    [doi:10.1107/S0108768196099375]

Organic molecular crystals: interaction, localization and transport phenimena by E. A. Silinsh and V. Cápek

Acta Cryst. (1997). B53, 1027    [doi:10.1107/S0108768196099363]

Physics and chemistry at oxide surfaces by C. Noguera

Acta Cryst. (1997). B53, 1027    [doi:10.1107/S0108768196099351]

Synchrotron radiation techniques in industrial, chemical and materials science edited by K. L. D'Amico, L. J. Terminello and D. K. Shuh

international union of crystallography

Acta Cryst. (1997). B53, 1028-1029    [doi:10.1107/S010876819609934X]

Prices of IUCr Journals

Acta Cryst. (1997). B53, 1031-1037

Subject index to volume B53 (1997)

Acta Cryst. (1997). B53, 1038-1039

Formula index to volume B53 (1997)

Acta Cryst. (1997). B53, 1040-1045

Author index to volume B53 (1997)

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