Acta Crystallographica Section B

Structural Science

Volume 61, Part 6 (December 2005)

Cover illustration: The arrangements of boxes shown represent the possible packing patterns of four molecules (each with dimensions L, M and S) in a unit cell, as described by the Box Model of crystal packing [Pidcock & Motherwell (2004). Cryst. Growth Des., 4, 611-620]. Application of this model to experimental P21/c structures revealed that the lower surface area packing patterns, for example 221L and 221M, are populated to a much greater extent than the higher surface area packing patterns of 114M and 114L. This finding indicates molecular shape is of primary importance in crystal packing [Pidcock & Motherwell (2004), Acta Cryst. B60, 539-546; Pidcock & Motherwell (2004), Acta Cryst. B60, 725-733].

• research papers

research papers

Acta Cryst. (2005). B61, 601-607  [ doi:10.1107/S0108768105033008 ] A reinterpretation of the phase transitions in Na2CO3 A. Arakcheeva and G. Chapuis Synopsis: The interactions between C atoms and Na ions can be directly associated with the phase transitions in sodium carbonate, Na2CO3. By lowering the temperature, the coordination number of the C atoms increases from 3 to 7 in the second coordination sphere. The behavior of the carbonate ion is influenced by the neighbouring Na ions. Online 14 November 2005

Acta Cryst. (2005). B61, 608-615  [ doi:10.1107/S0108768105031034 ] X-ray diffraction study for one-dimensional ionic conductors Kx(Ga1 - yAly)2 + xTi2 - xO7 (x 0.14, y 0.10, 0.23, 0.39) Y. Michiue and S. Yoshikado Synopsis: Probability density distributions of the K ion in the title compounds were examined by single-crystal X-ray diffraction. A Gram-Charlier expansion was used for the atomic displacement parameters. Online 14 November 2005

Acta Cryst. (2005). B61, 616-626  [ doi:10.1107/S0108768105028879 ] Tilt and acoustic instabilities in ABX4, A2BX4 and ABX3 perovskite structure types: their role in the incommensurate phases of the organic-inorganic perovskites I. P. Swainson Synopsis: An examination of tilts and their relationships to acoustic modes is made for simple perovskite structure types. The origin of the incommensurate phases in the organic-inorganic perovskites is shown to be due to the coupling of low-frequency buckling modes which are intrinsic to the inorganic layer with the onset of orientational ordering of the amine cations. Online 14 November 2005

Acta Cryst. (2005). B61, 627-634  [ doi:10.1107/S0108768105026698 ] Second-degree twinning and dynamic disorder in the crystal structure of deca-dodecasil 3R V. Langer, L. Smrcok, D. Tunega and G. Wirnsberger Synopsis: Twinning in the structure of deca-dodecasil 3R has been resolved and a new structure determination is presented. Ab initio molecular dynamics calculations show that disorder in deca-dodecasil 3R is dynamic rather than static in nature. Online 14 November 2005

Acta Cryst. (2005). B61, 635-655  [ doi:10.1107/S0108768105031125 ] Geometrical parameterization of the crystal chemistry of P63/m apatites: comparison with experimental data and ab initio results P. H. J. Mercier, Y. Le Page, P. S. Whitfield, L. D. Mitchell, I. J. Davidson and T. J. White Synopsis: A geometrical crystal-chemical model of P63/m apatite based on a specific set of bond-length and bond-angle parameters is derived. The model is used to compare the experimental results of apatite materials studied by single-crystal and Rietveld analysis with computed results of ab initio simulations, which are also used to predict the structures of hypothetical compounds which have not yet been studied. Online 14 November 2005

Acta Cryst. (2005). B61, 656-662  [ doi:10.1107/S0108768105026480 ] Incommensurately modulated ordering of tetrahedral chains in Ca2Fe2O5 at elevated temperatures H. Krüger and V. Kahlenberg Synopsis: Single-crystal XRD experiments at 1100 K show that the compound Ca2Fe2O5 forms an incommensurately modulated structure. The modulation can be explained with aperiodic alternation of enantiomorphic tetrahedral chains. Online 14 November 2005

Acta Cryst. (2005). B61, 663-668  [ doi:10.1107/S010876810503212X ] Structures of Na9[SO4]4X·2H2O2, where X = Cl or Br, in which the halide anions orchestrate extended orientation sequences of H2O2 solvate molecules R. G. Pritchard, Z. Begum, Y. F. Lau and J. Austin Synopsis: Both Na9[SO4]4Cl·2H2O2 and its newly discovered bromide analogue are extremely stable and can be used as sources of anhydrous H2O2 or, in the presence of H+, dihalogen. Despite being composed of small, inorganic molecules and ions, long H2O2 orientation sequences require the chloride unit-cell dimensions to be exceptionally large. The extended patterns of H2O2 orientations can be linked to displacements of the eight sodium cations that coordinate each halide anion. Online 14 November 2005

Acta Cryst. (2005). B61, 669-674  [ doi:10.1107/S0108768105028387 ] Structural characterization of Cd3(O3PC2H4CO2)2·2H2O from in-house X-ray powder data and NMR N. Bestaoui, X. Ouyang, F. Fredoueil, B. Bujoli and A. Clearfield Synopsis: The crystal structure of Cd3(O3PC2H4CO2)2·2H2O has been determined from in-house powder data. This compound crystallizes in the monoclinic system and shows a layered-type structure in which the layers are connected by the ligand into a three-dimensional array. Online 14 November 2005

Acta Cryst. (2005). B61, 675-688  [ doi:10.1107/S0108768105026662 ] Three modulation patterns in four related [M(H2O)2(15-crown-5)](NO3)2 structures X. Hao, S. Parkin and C. P. Brock Synopsis: The modulated structures of [M(H2O)2(15-crown-5)](NO3)2, M = Cu, Zn, Mg and Co, have been redetermined at 294 and 90 K. Significant problems in the original determinations have been fixed, the relationships between the structures have been identified and a reason for the modulations has been proposed. Online 14 November 2005

Acta Cryst. (2005). B61, 689-699  [ doi:10.1107/S0108768105031356 ] The unusual phases of anhydrous and hydrated pinacol X. Hao, S. Parkin and C. P. Brock Synopsis: The structure of highly twinned pinacol monohydrate has been determined, and the structures of anhydrous pinacol and its two other known hydrates have been reinvestigated. Online 14 November 2005

Acta Cryst. (2005). B61, 700-709  [ doi:10.1107/S0108768105026686 ] Isostructural phase transition in m-carboxyphenylammonium monohydrogenphosphite E.-E. Bendeif, S. Dahaoui, M. François, N. Benali-Cherif and C. Lecomte Synopsis: The isostructural phase transition of the title compound and its 3.6 K hysteresis (Tc = 246 K on cooling and 249.6 K on heating) have been characterized by X-ray diffraction and differential scanning calorimetry. Online 14 November 2005

Acta Cryst. (2005). B61, 710-716  [ doi:10.1107/S0108768105025991 ] Structure and intermolecular interactions of glipizide from laboratory X-ray powder diffraction J. C. Burley Synopsis: The crystal structure of the major diabetes treatment glipizide (glucotrol) has been determined. Intermolecular forces have been quantitatively evaluated from analysis of the thermal expansion of the lattice. Online 14 November 2005

Acta Cryst. (2005). B61, 717-723  [ doi:10.1107/S0108768105026327 ] Pressure-induced polymorphism in cyclopropylamine P. Lozano-Casal, D. R. Allan and S. Parsons Synopsis: The crystal structure of cyclopropylamine has been determined at 1.2 GPa using high-pressure single-crystal X-ray diffraction techniques. The structure of this previously unobserved phase is orthorhombic. Online 14 November 2005

Acta Cryst. (2005). B61, 724-730  [ doi:10.1107/S0108768105030077 ] Variable-temperature neutron diffraction studies of the short, strong hydrogen bonds in the crystal structure of pyridine-3,5-dicarboxylic acid J. A. Cowan, J. A. K. Howard, G. J. McIntyre, S.M.-F. Lo and I. D. Williams Synopsis: Temperature-dependent proton migration has been observed in pyridine-3,5-dicarboxylic acid and also in pyridine-3,5-dicarboxylic acid in which the carboxylic acid protons have been replaced by deuterons. Online 14 November 2005

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