Acta Crystallographica Section B

Structural Science

Volume 62, Part 3 (June 2006)

Cover illustration: Room-temperature structure of the cation-deficient perovskite, Nd0.7Ti0.9Al0.1O3 [Zhang et al. (2006). Acta Cryst. B62, 60-67]. The superlattice peaks associated with out-of-phase octahedral tilting (shown) have intensities consistent with tilting around the x and y axes (sum of a- and c-), but tilting around the y axis (contribution b-) evidently does not occur. The tilt system in Glazer's notation is thus a-b0c-, and the space group and structure are found from the tree displayed. Two views of the structure are shown - the (Ti/Al)O6 are shown as octahedra, the Ti/Al atom being visible within them, and the darker and lighter spheres outside these octahedra represent fully and partly occupied layers of Nd, respectively. The octahedral tilting, around both x and y axes, is clearly seen.

• feature articles
• research papers

feature articles

Acta Cryst. (2006). B62, 341-383  [ doi:10.1107/S0108768106008640 ] On the mechanism of some first-order enantiotropic solid-state phase transitions: from Simon through Ubbelohde to Mnyukh F. H. Herbstein Synopsis: An integrated and comparative study of more than 20 enantiotropic solid-state phase transitions shows that these are all first-order and proceed by a `nucleation and growth' mechanism in accordance with the description set out especially by Yuri Mnyukh. Online 15 May 2006

research papers

Acta Cryst. (2006). B62, 384-396  [ doi:10.1107/S0108768106002448 ] Structure determination of A2M3+TaO6 and A2M3+NbO6 ordered perovskites: octahedral tilting and pseudosymmetry P. W. Barnes, M. W. Lufaso and P. M. Woodward Synopsis: The crystal structures of six A2M3+M5+O6 ordered perovskites as determined from X-ray and neutron powder diffraction data are reported here. These samples show a high degree of pseudosymmetry that complicates the interpretation of the powder diffraction data. Correct space-group assignments were made through the systematic analysis of the supercell reflections, splitting of the fundamental perovskite peaks and crystal chemical considerations. Online 15 May 2006

Acta Cryst. (2006). B62, 397-410  [ doi:10.1107/S010876810600262X ] Structure prediction of ordered and disordered multiple octahedral cation perovskites using SPuDS M. W. Lufaso, P. W. Barnes and P. M. Woodward Synopsis: The capabilities of the program SPuDS have been extended to predict crystal structures of A2MM'X6 ordered double perovskites. Its accuracy and potential applications are discussed. Online 15 May 2006

Acta Cryst. (2006). B62, 411-416  [ doi:10.1107/S0108768106009335 ] `Ionic' size differences from bond-valence parameters and from ionic radii E. Keller and V. Krämer Synopsis: Expectation values for size differences between pairs of `ions' (atoms in oxidation states 0) embedded into similar coordination environments are calculated from bond-valence parameter and ionic radii tables. Online 15 May 2006

Acta Cryst. (2006). B62, 417-423  [ doi:10.1107/S0108768106009359 ] Experimental versus expected halide-ion size differences; structural changes in three series of isotypic bismuth chalcogenide halides E. Keller and V. Krämer Synopsis: Experimentally determined, halide-ion size differences are compared with expected sizes in the three series of isotypic bismuth chalcogenide halide compounds KBi6O9X, BiOX and BiSX. Online 15 May 2006

Acta Cryst. (2006). B62, 424-430  [ doi:10.1107/S0108768106010664 ] Compressibility of the nitridosilicate SrYb[Si4N7] and the oxonitridoaluminosilicates MYb[Si4-xAlxOxN7-x] (x = 2; M = Sr, Ba) E. A. Juarez-Arellano, A. Friedrich, K. Knorr, A. Lieb, B. Winkler, M. Amboage, M. Hanfland and W. Schnick Synopsis: In situ high-pressure X-ray powder diffraction up to 42 GPa was performed in order to explore the compressibilities of the title compounds. The results show that the sialons MYb[Si4-xAlxOxN7-x] (x = 2; M = Sr, Ba) are more compressible than the nitridosilicate SrYb[Si4N7], while all phases are stable up to the highest pressures reached. Online 15 May 2006

Acta Cryst. (2006). B62, 431-439  [ doi:10.1107/S0108768106009384 ] Estimation of polyhedral compressibilities and structural evolution of GdFeO3-type perovskites at high pressures J. Zhao, N. L. Ross and R. J. Angel Synopsis: A new approach based on the bond-valence matching relation is developed to predict the detailed structural evolution of GeFeO3-type perovskites at high pressure from knowledge of the room-pressure structure and the high-pressure unit-cell parameters alone. Online 15 May 2006

Acta Cryst. (2006). B62, 440-446  [ doi:10.1107/S010876810600663X ] Na2Si3O7: an incommensurate structure with crenel-type modulation functions, refined from a twinned crystal H. Krüger, V. Kahlenberg and K. Friese Synopsis: A (3 + 1)-dimensional superspace model for the incommensurate structure of Na2Si3O7 is presented and refined from twinned X-ray diffraction data. Online 15 May 2006

Acta Cryst. (2006). B62, 447-456  [ doi:10.1107/S010876810600975X ] Structural complexity in minerals: twinning, polytypism and disorder in the crystal structure of polybasite, (Ag,Cu)16(Sb,As)2S11 M. Evain, L. Bindi and S. Menchetti Synopsis: The atomic structures of 222- and 221-polybasite have been solved and refined from X-ray diffraction data from twinned crystals at 100 and 120 K, respectively. A possible mechanism regulating the type of unit cell that is stabilized is proposed. Online 15 May 2006

Acta Cryst. (2006). B62, 457-466  [ doi:10.1107/S0108768106011207 ] A comparative crystallochemical analysis of binary compounds and simple anhydrous salts containing pyramidal anions LO3 (L = S, Se, Te, Cl, Br, I) V. A. Blatov and M. V. Peskov Synopsis: A comparative analysis of simple anhydrous salts My(LO3)z (L = S, Se, Te, Cl, Br, I) showed their relationships to six types of binary compounds (NaCl, NiAs, PoCl2, Tl2S2, ZnTe, rutile). It has been established that in 36 out of the 61 salts at least one ion array has the topology of close packing or the body-centred cubic lattice. Online 15 May 2006

Acta Cryst. (2006). B62, 467-473  [ doi:10.1107/S0108768106009517 ] Crystal structures of the trifluoromethyl sulfonates M(SO3CF3)2 (M = Mg, Ca, Ba, Zn, Cu) from synchrotron X-ray powder diffraction data R. Dinnebier, N. Sofina, L. Hildebrandt and M. Jansen Synopsis: The crystal structures of M(SO3CF3)2 (M = Mg, Ca, Ba, Zn, Cu) were determined using high-resolution X-ray powder diffraction data. Online 15 May 2006

Acta Cryst. (2006). B62, 474-479  [ doi:10.1107/S0108768106004629 ] Cis/trans isomers of PtX2L2 (X = halogen, L = neutral ligand); the crystal structure of trans-dichlorobis(dimethyl sulfide)platinum(II) and the pressure dependence of its unit-cell dimensions C. Hansson, S. Carlson, D. Giveen, M. Johansson, S. Yong and Å. Oskarsson Synopsis: The crystal structure of trans-PtCl2(dms)2 (dms is dimethyl sulfide) has been determined from single-crystal diffraction data and the pressure dependence of its unit-cell dimensions has been studied with diamond-anvil cells up to 8.0 GPa using powder diffraction. trans-PtCl2(dms)2 adopts the molecular point group Ci, which is the most frequently occurring point group for trans-PtX2L2 complexes (78%) as observed in the Cambridge Structural Database (CSD), followed by C1 (16%). No preference for either trans- or cis-PtX2L2 is found in the CSD. Online 15 May 2006

Acta Cryst. (2006). B62, 480-487  [ doi:10.1107/S0108768105040590 ] X-ray crystallographic structures of enamine and amine Schiff bases of pyridoxal and its 1:1 hydrogen-bonded complexes with benzoic acid derivatives: evidence for coupled inter- and intramolecular proton transfer S. Sharif, D. R. Powell, D. Schagen, T. Steiner, M. D. Toney, E. Fogle and H.-H. Limbach Synopsis: Schiff base structures containing pyridoxal (PL) and their 1:1 acid-base adducts are reported and serve as models for the coenzyme pyridoxal-5'-phosphate (PLP) in the dependent enzymes. They allow the study of the intramolecular OHN hydrogen bond of PL/PLP Schiff bases and the H-acceptor properties of their pyridine rings. Online 15 May 2006

Acta Cryst. (2006). B62, 488-497  [ doi:10.1107/S0108768106000620 ] S,S-1,2-Dicyclohexylethane-1,2-diol and its racemic compound: a striking exception to Wallach's rule B. O. Patrick and C. P. Brock Synopsis: Analyses of the crystal structures of enantiopure S,S-1,2-dicyclohexylethane-1,2-diol and its racemic compound suggest a reason why crystals of any enantiopure material might be expected to be less dense than crystals of the corresponding racemic compound and to be more likely to have Z' > 1. Online 15 May 2006

Acta Cryst. (2006). B62, 498-505  [ doi:10.1107/S0108768106012018 ] 17 salts of ephedrine: crystal structures and packing analysis E. A. Collier, R. J. Davey, S. N. Black and R. J. Roberts Synopsis: The structures of anhydrous ephedrine and ephedrine hemihydrate together with 17 salts of the base are reported. It is evident that the observed packings are in most cases related to those of the neutral molecule, incorporating both bilayer and conformational elements. Online 15 May 2006

Acta Cryst. (2006). B62, 506-512  [ doi:10.1107/S010876810600930X ] The incommensurately modulated structure of a tricyclic natural-product-like compound of empirical formula C22H20O3 N. Guiblin, C. A. Fuhrer, R. Häner, H. Stoeckli-Evans, K. Schenk and G. Chapuis Synopsis: The single-crystal incommensurately modulated structure of 3,4-diphenyl-2a,5a,6,7,8,8a,8b-heptahydrofuro[4,3,2-de]chromen-2-one, C22H20O3, is presented. Online 15 May 2006

Acta Cryst. (2006). B62, 513-520  [ doi:10.1107/S0108768106008329 ] Chemical bonding in pentaerythritol at very low temperature or at high pressure: an experimental and theoretical study E. A. Zhurova, V. G. Tsirelson, V. V. Zhurov, A. I. Stash and A. A. Pinkerton Synopsis: Atomic interactions in the pentaerythritol crystal based on the experimental electron density at 15 K, and theoretical calculations based on the experimental molecular geometries obtained at room and low (15 K) temperatures, as well as at high pressure (1.15 GPa) have been analyzed and compared. Online 15 May 2006

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