First Mixed Alkaline Uranyl Molybdates: Synthesis and Crystal Structures of CsNa(3) (UO(2))(4)O(4)(Mo(2)O(8)) and Cs(2)Na(8) (UO(2))(8)O(8)(Mo(5)O(20))

Nazarchuk, E. V., Siidra, O. I., Krivovichev, S. V., Malcherek, T. and Depmeier, W. (2009) First Mixed Alkaline Uranyl Molybdates: Synthesis and Crystal Structures of CsNa(3) (UO(2))(4)O(4)(Mo(2)O(8)) and Cs(2)Na(8) (UO(2))(8)O(8)(Mo(5)O(20)) Zeitschrift Fur Anorganische Und Allgemeine Chemie, 635 (8). pp. 1231-1235. DOI 10.1002/zaac.200801162.

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Two new mixed alkaline uranyl molybdates CsNa(3)[(UO(2))(4)O(4)Mo(2)O(8)] (1) and Cs(2)Na(8)[(UO(2))(8)O(8)(Mo(5)O(20))] (2) have been obtained by high-temperature solid state reactions. Their crystal structures have been solved by direct methods: Compound 1: triclinic, P (1) over bar, a = 6.46(1), b = 6.90(1), c = 11.381(2) angstrom, alpha = 84.3(1), beta = 91.91(1), gamma = 80.23(1)degrees, V = 488.6(2) angstrom(3), R(1) = 0.06 for 2865 unique reflections with |F(o)| >= 4 sigma(F); Compound 2: orthorhombic, Ibam, a = 6.8460(2), b = 23.3855(7), c = 12.3373(3) angstrom, V = 1975.2(1) angstrom(3), R(1) = 0.049 for 2120 unique reflections with |F(o)| >= 4 sigma(F) The structure of 1 contains complex sheets of UrO(5) pentagonal bipyramids and molybdenum polyhedra. The sheets have [(UO(2))(2)O(2)(MoO(5))] composition. Natrium and cesium atoms are located in the interlayer space. Cesium items are situated between the molybdenum clusters, whereas natrium atoms are segregated between the uranyl complexes. The large Cs(+) ions are localized between the Mo(2)O(9) groups and force the molybdenum polyhedra to rotate relative to the [(UO(2))(2)O(2)(MoO(5))] sheets. Such rotation is impossible for U(6+) polyhedra due to their rigid edge-sharing complexes. The distance between the U(6+) polyhedra vertices of neighboring layers is 3.8 angstrom, that allows the Na(+) ion to be positioned between the uranyl groups. The crystal structure of 2 is based upon a framework consisting of [(UO(2))(2)O(2)(MoO(5))] sheets parallel to (010). The sheets are linked into a 3-D framework by sharing vertices with the Mo(2)O(4) tetrahedra, located between the sheets. Each MoO(4) tetrahedron shares two of its corners with two MoO(6) octahedra in the sheet above, and the other two with MoO(6) octahedra of the sheet below. Thus four MoO(6) octahedra and one MoO(4) tetrahedron form chains of composition Mo(5)O(18). The resulting framework has a system of channels occupied by the Cs(+) and Na(+) ions.

Document Type: Article
Keywords: Uranium Molybdenum Uranyl molybdates Crystal structures chemistry polyhedra iriginite fuel
Research affiliation: Kiel University
DOI etc.: 10.1002/zaac.200801162
ISSN: 0044-2313
Date Deposited: 22 Dec 2011 05:38
Last Modified: 08 Oct 2012 10:10

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