Acta Crystallographica Section B

Structural Science

Volume 66, Part 6 (December 2010)

Cover illustration: The clusters shown on the cover image belong to the fundamental structural building units of cF(5928-x)-Al56.6Cu3.9Ta39.5, x = 20, one representative of a family of cluster-based tantalum copper aluminides with giant unit cells hosting up to more than 20 000 atoms. Their structures can be geometrically described as packings of clusters such as fullerenes, dodecahedra, pentagonal bifrusta, hexagonal bipyramids and Friauf polyhedra [Conrad et  al. (2009). Acta Cryst. B65, 318-325; see also Weber et  al. (2009). Acta Cryst. B65, 308-317].

• research papers

research papers

Acta Cryst. (2010). B66, 579-584  [ doi:10.1107/S0108768110039686 ] Determination of the crystal structure of magnesium perchlorate hydrates by X-ray powder diffraction and the charge-flipping method K. Robertson and D. Bish Synopsis: The crystal structures of the magnesium perchlorate tetrahydrate and dihydrate were determined using the charge-flipping method and powder diffraction data. The structural evolution of the Mg(ClO4)2·nH2O system during dehydration was examined. Online 10 November 2010

Acta Cryst. (2010). B66, 585-593  [ doi:10.1107/S0108768110035792 ] The modulated structure of the calcium aluminate Ca6(AlO2)12·Bi2O3 O. Pérez, S. Malo and M. Hervieu Synopsis: The structure of incommensurate bismuth calcium aluminate, Bi2Ca6Al12O27, has been solved using single-crystal X-ray diffraction data. The origin of the modulation is related to the ordering of Bi2O9Lp2 clusters within tunnels within the Ca6Al12O24 framework. Online 17 November 2010

Acta Cryst. (2010). B66, 594-602  [ doi:10.1107/S0108768110038620 ] Structure and electrical properties of the new pyrochlore-type protonic solid electrolyte K0.88Nb2O7.58H4.28 O. Smirnova, N. Kumada, T. Takei, Y. Yonesaki, M. Yashima and N. Kinomura Synopsis: Single-crystal, synchrotron powder X-ray diffraction and neutron powder diffraction studies of the novel pyrochlore-type compound with the structural formula K0.88(OH)0.54H1.66(H2O)1.04Nb2O6 are reported. Owing to the extended stability range and resistance to water solubility, the compound can be considered as a candidate for intermediate temperature solid-oxide fuel-cell applications. Online 10 November 2010

Acta Cryst. (2010). B66, 603-614  [ doi:10.1107/S0108768110040802 ] Crystal chemistry of transition metal diarsenates M2As2O7 (M = Mn, Co, Ni, Zn): variants of the thortveitite structure M. Weil and B. Stöger Synopsis: Mn2As2O7 and the high-temperature -M2As2O7 (M = Mn, Co, Ni) polymorphs crystallize in the thortveitite aristotype structure, whereas the low-temperature -M2As2O7 polymorphs and -Zn2As2O7 are hettotypes. Online 17 November 2010

Acta Cryst. (2010). B66, 615-621  [ doi:10.1107/S0108768110039327 ] Structure of N-(5-ethyl-[1,3,4]-thiadiazole-2-yl)toluenesulfonamide by combined X-ray powder diffraction, 13C solid-state NMR and molecular modelling A. Hangan, G. Borodi, X. Filip, C. Tripon, C. Morari, L. Oprean and C. Filip Synopsis: A multi-technique approach that combines X-ray powder diffraction (XRPD) with 13C solid-state NMR (SSNMR), and molecular modelling using the GIPAW gauge (gauge including projector augmented-wave) method is employed for structural determination on microcrystalline powders. This approach is shown to be very robust in simplifying the crystal structure search protocol, as well as in clearly identifying the non-covalent interactions (C-H) responsible for stabilizing the three-dimensional crystal structure of the title compound. Online 10 November 2010

Acta Cryst. (2010). B66, 622-638  [ doi:10.1107/S0108768110040024 ] Thermal motion of tert-butyl groups III. tert-Butyl substituents in aromatic hydrocarbons, the view from the bottom of the well J. Frey, S. I. Khan, C. B. Knobler, D. A. Lightner, E. F. Maverick, D. J. Phillips, Z. Rappoport and K. N. Trueblood Synopsis: Low-temperature crystal studies of five strained aromatic hydrocarbons yield anisotropic displacement parameters that vary widely in magnitude and precision. The rigidity of tert-butyl substituents is tested; thermal motion analysis indicates that crowded ortho tert-butyls do not `move' with respect to the aromatic core, while rigid-body models for meta and para tert-butyls suggest low rotation barriers (4-10 kJ mol-1), in some cases with additional motion of a tert-butyl methyl group. Online 10 November 2010

Acta Cryst. (2010). B66, 639-646  [ doi:10.1107/S0108768110036608 ] Direct observation of arylnitrene formation in the photoreaction of arylazide crystals T. Takayama, T. Mitsumori, M. Kawano, A. Sekine, H. Uekusa, Y. Ohashi and T. Sugawara Synopsis: Seven kinds of arylazide crystals were investigated but only one, 2-azidobiphenyl, formed an observable nitrene on exposure to UV light at 80 K. The structure of a single crystal containing both starting material and unstable 2-biphenylnitrene was analyzed using X-rays. Online 10 November 2010

Acta Cryst. (2010). B66, 647-661  [ doi:10.1107/S010876811003661X ] Direct observation of various reaction pathways of arylnitrenes in different crystal environments caused by acid-base complex formation T. Mitsumori, A. Sekine, H. Uekusa and Y. Ohashi Synopsis: Various reaction pathways of arylnitrenes produced by photo-irradiation in complex crystals composed of 2-, 3- or 4-azidobenzoic acid and a diaryl- or dicyclohexylamine were directly observed by X-ray crystal structure analysis. Online 10 November 2010

Acta Cryst. (2010). B66, 662-677  [ doi:10.1107/S0108768110040243 ] Structures of cyclic dipeptides: an X-ray and computational study of cis- and trans-cyclo(Pip-Phe), cyclo(Pro-Phe) and their N-methyl derivatives M. Budesinsky, I. Cisarova, J. Podlaha, F. Borremans, J. C. Martins, M. Waroquier and E. Pauwels Synopsis: The crystal structures of a set of eight closely related cyclodipeptides are determined. By comparing with density functional theory gas-phase and periodic calculations, the intra- and intermolecular interactions governing these crystals are investigated. Online 17 November 2010

Acta Cryst. (2010). B66, 678-686  [ doi:10.1107/S0108768110040760 ] Solid solution of two diastereomers of [3a(R,S),7a(R,S)]-3-[(1'R)-1-phenylethyl]perhydro-1,3-benzothiazol-2-iminium chloride A. Plutecka, U. Rychlewska, N. Prusinowska and J. Gawronski Synopsis: The solid solution of two diastereomers of [3a(R,S),7a(R,S)]-3-[(1'R)-1-phenylethyl]perhydro-1,3-benzothiazol-2-iminium chloride has been studied by single-crystal X-ray diffraction, while density functional theory (DFT) calculations helped to establish the charge distribution within the thiazolidin-2-imine part of the molecular cation. The similarity of the molecular shapes and the formation of strong hydrogen bonds, unaffected by changes of chirality, explain the impossibility of resolving the diastereomers by crystallization. Online 10 November 2010

Acta Cryst. (2010). B66, 687-695  [ doi:10.1107/S0108768110040875 ] Electron density studies on hydrogen bonding in two chromone derivatives M. Malecka, L. Checinska, A. Rybarczyk-Pirek, W. Morgenroth and C. Paulmann Synopsis: The experimental electron densities of two chromone derivatives have been determined from X-ray synchrotron diffraction data at low temperature (100 K). The presence of intramolecular resonance-assisted hydrogen bonds and -electron delocalization within the hydrogen-bonded ring were confirmed by geometrical and topological parameters. Online 17 November 2010

Acta Cryst. (2010). B66, 696-707  [ doi:10.1107/S0108768110037055 ] Diffuse scattering study of aspirin forms (I) and (II) E. J. Chan, T. R. Welberry, A. P. Heerdegen and D. J. Goossens Synopsis: Full three-dimensional diffuse scattering data have been recorded for both polymorphic forms [(I) and (II)] of aspirin and these data have been analysed using Monte Carlo computer modelling. The observed scattering in form (I) is well reproduced by a simple harmonic model of thermally induced displacements. The data for form (II) show, in addition to thermal diffuse scattering (TDS) similar to that in form (I), diffuse streaks originating from stacking fault-like defects as well as other effects that can be attributed to strain induced by these defects. Online 10 November 2010

Copyright © International Union of Crystallography
IUCr Webmaster