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Single-crystal Data (single-crystal + data)
Selected AbstractsSynthesis, Crystal Structure, and Catalytic Properties of Novel Dioxidomolybdenum(VI) Complexes with Tridentate Schiff Base Ligands in the Biomimetic and Highly Selective Oxygenation of Alkenes and SulfidesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2010Abdolreza Rezaeifard Abstract Four novel dioxidomolybdenum(VI) complexes [MoO2(Lx)(CH3OH)] have been synthesized, using 2[(E)-(2-hydroxy-2-phenylethylimino)methyl]phenol derivatives as tridentate ONO donor Schiff base ligands (H2Lx) and MoO2(acac)2. A monoclinic space group was determined by X-ray crystallography from single-crystal data of a sample of these new complexes. The epoxidation of alkenes by using tert -butyl hydroperoxide and oxidation of sulfides to sulfoxides by urea hydrogen peroxide were efficiently enhanced with excellent selectivity under the catalytic influence these new MoVI complexes. The high efficiency and relative stability of the catalysts have been observed by turnover numbers and UV/Vis investigations. The electron-poor and bulky ligands promoted the effectiveness of the catalysts. [source] The revenge of the Patterson methods.JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2007In the present paper, the third and last of a series (the first two papers were dedicated to the crystal structure solution of proteins), the Patterson superposition method, based on the use of the symmetry minimum function, has been applied to powder diffraction patterns. The method has been modified to take into account the special challenges of this kind of data and to optimize the performance of the approach. The new algorithms have been implemented in a computer program and applied also to single-crystal data of small and medium-size crystal structures. The experimental results have been compared with those obtained via direct methods, so enabling the role and the perspectives of these two approaches in the global phasing problem to be established, no matter what the experimental technique (powder or single-crystal diffraction) or the size of the structures (small, medium or macro-molecules). [source] Symmetrization of diffraction peak profiles measured with a high-resolution synchrotron X-ray powder diffractometerJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2006H. Hibino The asymmetry of diffraction peak profiles observed with a high-resolution synchrotron powder X-ray diffractometer has been successfully removed by a double deconvolution method. In the first step, the asymmetry caused by the axial divergence aberration of the diffractometer is removed by a whole-pattern deconvolution method based on an a priori theoretical model for the aberration. In the second step, the residual asymmetry, the origin of which can be ascribed to the aberrations of the beamline optics, is also removed by a whole-pattern deconvolution method, based on an empirical model derived from the analysis of experimental diffraction peak profiles of a standard Si powder (NIST SRM640b). The beamline aberration has been modelled by the convolution of a pseudo-Voigt or Voigt function with an exponential distribution function. It has been found that the angular dependence of the asymmetry parameter in the exponential function is almost proportional to tan,, which supports the idea that the residual asymmetry should be ascribed mainly to the intrinsic asymmetry in the spectroscopic distribution of the source X-ray supplied by the beamline optics of the synchrotron facility. Recently developed procedures of whole-pattern deconvolution have been improved to treat the singularity of the instrumental function in the measured angular range. Formulae for the whole-pattern deconvolution based on the Williamson,Hall-type dependence of the width parameter of the instrumental function have also been developed. The method was applied to the diffraction intensity data of a standard ZnO powder sample (NIST SRM674) measured with a high-resolution powder diffractometer on beamline BL4B2 at the Photon Factory. The structure parameters of ZnO were refined from the integrated peak intensities, which were extracted by an individual profile fitting method applying symmetric profile models. The refined structure parameters coincide fairly well with those obtained from single-crystal data. [source] Two new silicate structures based on a rhodesite-type heteropolyhedral microporous frameworkACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2010Marcella Cadoni Two new members of the mero-plesiotype rhodesite series [Sr2Na2(Si8O19)·4H2O, abbreviated as TR09; SrNa4(Si8O19)·4H2O, TR10] have been hydrothermally synthesized in Teflon-lined autoclaves at 503,K and structurally characterized using X-ray diffraction single-crystal data. The crystal structures were solved by direct methods and refined to R = 0.021 [TR09; 3317 reflections with Io > 2,(Io)] and R = 0.033 [TR10; 5007 reflections with Io > 2,(Io)]. Both structures are based on a rhodesite-type microporous heteropolyhedral framework, where two types of channels are within the double silicate layer that alternates with an `octahedral' O sheet. The large Sr2+ cation constrains to the roughly ellipsoidal shape of the channels. The H2O molecules are located both in the O sheets and in the channels, where they are loosely hydrogen bonded. The crystal-chemical features that allow flexibility to the rhodesite-type microporous heteropolyhedral framework and make it interesting for possible technological applications are discussed. [source] New RE microporous heteropolyhedral silicates containing 41516182 tetrahedral sheetsACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2010Marcella Cadoni Four heteropolyhedral microporous silicates, A3RESi6O15·2.25H2O, crystallizing in the Cmm2 space group and based on 41516182 tetrahedral sheets [A3 = Na2.74K0.26, RE = Ce, abbreviated as TR05; TR06: A3 = Na2.72K0.28, RE = La; TR07: A3 = Na3, RE = La; TR08: A3 = Na2.74(H3O)0.26, RE = La0.68Eu0.32] have been hydrothermally synthesized in Teflon-lined autoclaves at 503,K and structurally characterized using X-ray diffraction single-crystal data. Except for TR05, diffraction data have been collected on {001} twins by merohedry. The four structures are isotypic and based on strongly corrugated 41516182 silicate sheets interconnected along [010] by seven-coordinated RE polyhedra to form a microporous heteropolyhedral framework. The framework is crossed by three systems of ellipsoidal channels that host H2O molecules and alkaline ions. The channels run either parallel or perpendicular to the silicate sheets; the largest effective channel width is 4.7,×,2,Å. In TR08 some (H3O)+ replaces alkalis. Although the H atoms have not been localized, the configuration of the hydrogen bonding has been deduced from bond lengths and angles. [source] Structure of caesium disulfate at 120 and 273,KACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2009Kenny Ståhl The crystal structures of Cs2S2O7 at 120 and 273,K have been determined from X-ray single-crystal data. Caesium disulfate represents a new structure type with a uniquely high number of independent formula units at 120,K: In one part caesium ions form a tube surrounding the disulfate ions, [Cs8(S2O7)6+]n; in the other part a disulfate double-sheet sandwiches a zigzagging caesium ion chain, [Cs2(S2O7)6,]n. Caesium disulfate shows an isostructural order,disorder transition between 230 and 250,K, where two disulfate groups become partially disordered above 250,K. The Cs+ -ion arrangement shows a remarkable similarity to the high-pressure RbIV metal structure. [source] Structure determination of seven phases and solvates of Pigment Yellow 183 and Pigment Yellow 191 from X-ray powder and single-crystal dataACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2009Svetlana N. Ivashevskaya The crystal structures of two industrially produced laked yellow pigments, Pigment Yellow 183 [P.Y. 183, Ca(C16H10Cl2N4O7S2), , phase] and Pigment Yellow 191 [P.Y. 191, Ca(C17H13ClN4O7S2), , and , phases], were determined from laboratory X-ray powder diffraction data. The coordinates of the molecular fragments of the crystal structures were found by means of real-space methods (simulated annealing) with the program DASH. The coordinates of the calcium ions and the water molecules were determined by combining real-space methods (DASH and MRIA) and repeated Rietveld refinements (TOPAS) of the partially finished crystal structures. TOPAS was also used for the final Rietveld refinements. The crystal structure of ,-P.Y. 183 was determined from single-crystal data. The , phases of the two pigments are isostructural, whereas the , phases are not. All four phases exhibit a double-layer structure, built from nonpolar layers containing the C/N backbone and polar layers containing the calcium ions, sulfonate groups and water molecules. Furthermore, the crystal structures of an N,N -dimethylformamide solvate of P.Y. 183, and of P.Y. 191 solvates with N,N -dimethylformamide and N,N -dimethylacetamide were determined by single-crystal X-ray analysis. [source] Rietveld refinement of a wrong crystal structureACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2007Christian Buchsbaum Rietveld refinements are generally used to confirm crystal structures solved from powder diffraction data. If the Rietveld refinement converges with low R values and with a smooth difference curve, and the structure looks chemically sensible, the resulting structure is generally considered to be close to the correct crystal structure. Here we present a counter example: The Rietveld refinement of the X-ray powder pattern of ,-quinacridone with the crystal structure of ,-quinacridone gives quite a smooth difference curve; the resulting crystal structure looks reasonable in terms of molecular conformation, molecular packing and intermolecular hydrogen bonds. However, neither the lattice parameters, the molecular packing nor the conformation of the molecules show any similarity with the actual structure, which was determined from single-crystal data. This example shows that a successful Rietveld refinement is not always final proof of the correctness of a crystal structure; in special cases the resulting crystal structure may still be wrong. [source] The high-pressure form of cadmium vanadate, CdV2O6ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2007Alexei A. Belik The crystal structure of a new high-pressure modification of cadmium divanadium hexaoxide, CdV2O6, was refined from X-ray single-crystal data. It contains zigzag chains of edge-sharing VO6 octahedra. Octahedra in adjacent chains share corners and form corrugated layers. Octahedrally coordinated Cd atoms, which lie on twofold axes, are situated between the layers. The columbite-like structure results in a strong distortion of the CdO6 octahedra which may be stabilized only at high pressure. [source] Sodium magnesium bis(vanadate) pyrovanadate: Na6Mg2(VO4)2(V2O7)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2004Alexander Mitiaev The crystal structure of the new complex vanadium oxide Na6Mg2(VO4)2(V2O7) was solved from X-ray single-crystal data. The structure contains VO4 tetrahedra and MgO6 octahedra, linked by corners and forming a complex three-dimensional framework. A half of the VO4 tetrahedra are connected only to MgO6 octahedra, whereas the others are corner-sharing, forming V2O7 pyrovanadate groups with statistically random orientations. One unique Mg atom is located at an inversion centre, while the other Mg atom, one unique V atom and five unique O atoms lie on mirror planes. [source] Compressed Octahedral Coordination in Chain Compounds Containing Divalent Copper: Structure and Magnetic Properties of CuFAsF6 and CsCuAlF6CHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2004Zoran Mazej Dr. Abstract Crystal structures and magnetic investigations of CuFAsF6 and CsCuAlF6 are reported. Together with KCuAlF6, these appear to be the only examples of Jahn,Teller pure CuII compounds containing only one type of ligand that exhibits a compressed octahedral coordination geometry. The Rietveld method has been used for refining the CsCuAlF6 structure based on neutron powder diffraction data at 4 K. The compound crystallizes in space group Pnma (no. 62) with a=7.055(1), b=7.112(1), c=10.153(1) Å and Z=4 at 4 K. The structure is built from infinite [CuF5]n3n, chains of [CuF6]4, octahedra running along the [1,0,0] direction and (AlF6)3, octahedra connected by corners in the trans position, thus giving rise to chains oriented along the [0,1,0] direction. Single crystals of CuFAsF6 were prepared under solvothermal conditions in AsF5 above its critical temperature. The structure was determined from single-crystal data. CuFAsF6 crystallises in the orthorhombic space group Imma (No. 74) with a=10.732(5), b=6.941(3), c=6.814(3) Å and Z=4 at 200 K. The structure can also be described in terms of one-dimensional infinite [CuF5]n3n, chains of tilted [CuF6]4, octahedra linked by trans -vertices running along the b axis. The [CuF5]n3n, chains are connected through [AsF6], units sharing joint vertices. The compressed octahedral coordination of CuII atoms in CuFAsF6 and CsCuAlF6 compounds at room temperature is confirmed by Cu K-edge EXAFS (extended x-ray absorption fine structure) analysis. For both compounds strong antiferromagnetic interactions within the [CuF5]n3n, chains were observed (,p=,290±10 K and ,p=,390±10 K for CuFAsF6 and CsCuAlF6, respectively). The peculiar magnetic behaviour of chain compounds containing divalent copper at low temperature could be related to uncompensated magnetic moments in the one-dimensional network. [source] | ||||||||||