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Selected Abstracts

Racemic calcium tartrate tetrahydrate [form (II)] in rat urinary stones

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2009
A. Le Bail
The title compound, [Ca(C4H4O6)]·4H2O, calcium tartrate tetrahydrate, is a new triclinic centrosymmetric form identified in rat kidney calculus. The crystal structure was determined from powder and single-crystal X-ray diffraction. The four water molecules belong to one square face of the Ca-atom coordination (a square antiprism), the four O atoms of the second square face coming from two tartrate anions, building infinite chains alternating Ca atom polyhedra and tartrate anions along a, with the chains cross-linked by a network of hydrogen bonds. [source]

Tetrastrontium dimanganese copper nonaoxide, Sr4Mn2CuO9

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2002
Ahmed El Abed
Single crystals of Sr4Mn2.09Cu0.91O9 have been grown by flux synthesis and the structure, closely related to the hexagonal perovskite 2H, was solved from single-crystal X-ray data in space group P321. The structure of Sr4Mn2CuO9 is composed of chains of face-sharing polyhedra with a sequence of two octahedra and one trigonal prism. The octahedra are filled by Mn atoms and the Cu atoms are randomly distributed at the centres of the square faces of the trigonal prism. A stacking fault is observed within one of the two chains, which can be attributed to a shifting of the chain along the c axis. [source]

The Valence Problem of Pd4Br4Te3

CHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2007
Manuel Janetzky
Abstract Pd4Br4Te3 was prepared from Pd, Te, and PdBr2 at 700,K. Its structure was determined by single-crystal X-ray diffraction to be triclinic, P, Pearson symbol aP22; a=842.5(2), b=845.0(3), c=864.8(3),pm; ,=82.55(3), ,=73.36(2), ,=88.80(2)°; Z=2. The Br and Te atoms are arranged according to the motif of cubic closest-packed spheres in which every 15th position is vacant; the Pd atoms occupy 8/15 of the octahedral voids. The symmetry relations with the packing of spheres are derived. Prominent structural units are hollow cuboctahedral [(PdBrTe)6] units, the Pd atoms are positioned near the centers of the square faces of the Br6Te6 cuboctahedra; the cuboctahedra and double-octahedral Pd2Br4Te6 units are connected to strands by sharing triangular Te3 faces. The strands are condensed by common Br atoms into layered assemblies. Conspicuously close TeTe contacts in the Te3 triangles indicate attractive TeTe interactions. The valence puzzle is resolved by the formula Pd(+II)4Br(,I)4Te(,4/3)3. Positive TeTe Mulliken orbital populations and the PdK, BrK, and TeLIII XANES spectra of Pd4Br4Te3 referenced to the spectra of PdBr2, K2PdBr6, PdTe, and PdTe2 are in accord with attractive TeTe interactions. The measured semiconducting and diamagnetic properties are compatible with the derived picture of chemical bonding in Pd4Br4Te3. Pd4Br4Te3 wurde aus Pd, Te und PdBr2 bei 700,K hergestellt. Nach der Strukturanalyse mittels Einkristall-Röntgenbeugung kristallisiert es triklin, P, Pearson-Symbol aP22; a=842,5(2), b=845,0(3), c=864,8(3),pm; ,=82,55(3), ,=73,36(2), ,=88,80(2)°; Z=2. Die Br- und Te-Atome sind nach dem Muster einer kubisch-dichtesten Kugelpackung angeordnet, in der jede 15-te Position unbesetzt ist; die Pd-Atome besetzen 8/15 der Oktaderlücken. Die Symmetriebeziehungen zur Kugelpackung werden hergeleitet. Im Zentrum unbesetzte, kuboktaedrische [(PdBrTe)6]-Baugruppen sind mit Pd2Br4Te6 -Doppeloktaedern über gemeinsame dreieckige Te3 -Flächen zu Strängen verknüpft, die ihrerseits über gemeinsame Br-Atome zu Schichten angeordnet sind. Auffällig kurze TeTe-Kontakte in den Te3 -Dreiecken deuten auf attraktive TeTe-Wechselwirkungen hin. Die zunächst rätselhafte Valenzsituation wird durch die Formulierung Pd(+II)4Br(,I)4Te(,4/3)3 gedeutet. Positive TeTe-Mulliken-Orbital-Populationen und die PdK -, BrK - und TeLIII -XANES-Spektren von Pd4Br4Te3 im Vergleich zu den Spektren von PdBr2, K2PdBr6, PdTe und PdTe2 bestätigen die attraktiven TeTe-Wechselwirkungen. Die gemessenen halbleitenden und diamagnetischen Eigenschaften von Pd4Br4Te3 passen zu dem abgeleiteten Bindungsmodell. [source]