Acta Crystallographica Section BActa Crystallographica Section B: Structural Science publishes papers in which structure is the primary focus of the work reported. The central themes of Structural Science are the acquisition of structural knowledge from novel experimental observations or from existing data, the correlation of structural knowledge with physico-chemical and other properties, and the application of this knowledge to solve problems in the structural domain. Structural Science has broad chemical coverage,...Synthesis and structural characteristics of lithocholate triads: steroid-type channels occupied by spacer fragments- May 15, 2008 Reported in this paper are the syntheses and X-ray investigations of C2 symmetrical molecular ABA triads consisting of two steroid units (lithocholic acid or its methyl ester) joined together by linkers derived from bifunctional molecules such as terephthalic acid or N,N-dicarboxypiperazine. Unlike their monomeric analogues, some of these compounds form inclusion complexes. All steroidal triads form crystals that are highly pseudo-centrosymmetric, in which the constituting molecules are held...http://scripts.iucr.org/cgi-bin/paper?bk5073 Five-coordinate copper(II) complexes: crystal structures, spectroscopic properties and new extended structural pathways of Cu(chelate)2XY, where chela- May 15, 2008 The crystal structures of four distortion isomers of the Cu(chelate)2X+ cation, where chelate = 2,2-bipyridine (bipy), 1,10-phenanthroline (phen) and di-2-pyridylamine (dpyam), X = a pseudohalide ligand (NCO, NCS, N3 and C2N3), have been compared by scatterplot analysis with 25 Cu(chelate)2XY complexes of known crystal structure. The four new complexes Cu(phen)2NCOBr (1), Cu(phen)2N3BPh4H2O (2), Cu(dpyam)2(N3)NO3H2O (3) and Cu(dpyam)2(N3)ClO4 (4) involve a near regular square-based pyramidal...http://scripts.iucr.org/cgi-bin/paper?bp5008 Dipolar Ctriple-bondN...Ctriple-bondN interactions in organic crystal structures: database analysis and calculation of interaction energies- May 15, 2008 The Cambridge Structural Database (CSD) has been used to study nonbonded interactions between dipolar cyano groups. The analysis shows that Ctriple-bondN...Ctriple-bondN interactions form in an analogous manner to those involving carbonyl groups, and with the same interaction motifs: a dominant antiparallel dimer (57.5%) together with smaller populations of perpendicular (19.4%) and sheared parallel (23.0%) motifs. Ab initio calculations using intermolecular perturbation theory (IMPT) show an...http://scripts.iucr.org/cgi-bin/paper?ws5064 Solid-state structures of the covalent hydrides germane and stannane- May 15, 2008 The low-temperature crystal structures of perdeuterogermane (m.p. 108K) and perdeuterostannane (m.p. 123K) are reported. The structures have been characterized from low-temperature (5K) high-resolution neutron powder diffraction experiments following sample preparation using in situ gas-condensation techniques. GeD4 crystallizes in an orthorhombic structure, space group P212121, with one molecule in the asymmetric unit, and with an average GeD bond length of 1.517(3). The SnD4 structure is...http://scripts.iucr.org/cgi-bin/paper?ws5063 Monitoring structural transformations in crystals. 12. Course of an intramolecular 4+4 photocycloaddition in a crystalFor Part 11 see Turowska-Tyrk, B- May 15, 2008 Variations in crystal and molecular structures, brought about by the intramolecular 4+4 photocycloaddition of bi(anthracene-9,10-dimethylene), were monitored using X-ray diffraction. The cell volume increased by 0.8% until the reaction was ca 40% complete, and afterwards decreased by 1.6% during the remainder of the photoreaction. The changes of the a and b lattice parameters were correlated with the changes of the molecular shape and packing. The distance between the directly reacting C atoms..http://scripts.iucr.org/cgi-bin/paper?bk5072 Orientational disorder in crystals of (NH4)3MoO3F3 and (NH4)3WO3F3- May 15, 2008 Triammonium trioxotrifluoromolybdate (NH4)3MoO3F3 (I) and trioxotrifluorotungstate (NH4)3WO3F3 (II) were synthesized in a single-crystal form and their structures were refined by X-ray diffraction. These two isostructural compounds belong to the elpasolite-type structure (cubic system, space group Fm3m, Z = 4). O and F atoms are randomly distributed in two independent positions 24(e) and 96(j) of the cubic unit cell, and the central atoms and the ammonium cation containing N2 are shifted from...http://scripts.iucr.org/cgi-bin/paper?bp5011 Conformational variability of molecules in different crystal environments: a database study- May 15, 2008 A methodology is described for analysing the Cambridge Structural Database (CSD) in terms of molecular conformations. Molecular species that have more than a single occurrence across the complete CSD are identified, either as the sole crystal component or co-crystallized with other components. Cluster analysis, based on a root-mean-square fit of coordinates and chemical connectivity, is performed to identify conformational variance for each molecule. Results are analysed in terms of the number..http://scripts.iucr.org/cgi-bin/paper?bs5057 A bond-valence investigation of two series of isostructural lanthanide compounds- May 15, 2008 Since the days of Pauling it has been tacitly assumed that the valence, which is distributed between the bonds to neighbouring atoms, is the stoichiometric valence, stoichV, which has integer values. It is shown here that this is not true. Instead, bond-valence sums (BVS) calculated for lanthanide (Ln) atoms of a series of garnet-type compounds Ln_3rm IIITe_2rm VILi_3rm IO_12 deviate significantly from stoichV. Values of (BVS)Ln of this series, plotted versus the element number ZLn, show the...http://scripts.iucr.org/cgi-bin/paper?sn0041 Disorder and pseudo-symmetry in octakis(trivinylsilyl)octasilicate- May 15, 2008 Octakis(trivinylsilyl)octasilicate was prepared by capping octaspherosilicate cubes, Si8O208, with trivinylsilyl groups in methanol solution. Crystals grown from CCl4 crystallize in the tetragonal space group I41. Systematic absences are consistent with the space group I41amd, although the Rint values clearly indicate 4m rather than 4mmm Laue symmetry. Structure solution and refinement show that the pseudo a-glide results from the approximate mbar 3m symmetry of the core (Si8O12)O_88- unit. The.http://scripts.iucr.org/cgi-bin/paper?ws5065 Structure and electron density of oxysulfide Sm2Ti2S2O4.9, a visible-light-responsive photocatalyst- May 15, 2008 We report the crystal structure and electron density of samarium titanium oxysulfide, Sm2Ti2S2O4.9, photocatalyst obtained through the Rietveld analysis, maximum-entropy method (MEM) and MEM-based pattern fitting of the high-resolution synchrotron powder diffraction data taken at 298.7K. The Sm2Ti2S2O4.9 has a tetragonal structure with the space group I4mmm. Refined occupancy factors at the equatorial' O1 and apical' O2 sites were 0.994(3) and 0.944(12), respectively, which strongly suggest...http://scripts.iucr.org/cgi-bin/paper?og5028 |