Dimensional reduction in alkali metal uranyl molybdates: Synthesis and structure of Cs-2 (UO2)O(MoO4)

Alekseev, E. V., Krivovichev, S. V., Armbruster, T., Depmeier, W., Suleimanov, E. V., Chuprunov, E. V. and Golubev, A. V. (2007) Dimensional reduction in alkali metal uranyl molybdates: Synthesis and structure of Cs-2 (UO2)O(MoO4) Zeitschrift Fur Anorganische Und Allgemeine Chemie, 633 (11-12). pp. 1979-1984. DOI 10.1002/zaac.200700270.

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Abstract

A new uranyl molybdate, Cs-2[(UO2)O(MoO4)] (1), has been prepared by high-temperature solid-state reactions. The structure has been solved by direct methods and refined to R-1 = 0.0284 for vertical bar F-0 vertical bar >= 4 sigma(F) The compound 1 is orthorhombic, Pca2(1), a = 12.018(2), b = 12.438(2), c = 17.917(3) angstrom, V = 2678.2(7) angstrom(3), Z = 12. The structure of 1 is based upon one-dimensional chains consisting of corner-sharing UO6 and MoO4 polyhedra. The UO6 square bipyramids share cis equatorial vertices to form zigzag chains that are further stabilized by bidendate MoO4 tetrahedra. The chains have composition [(UO2)O(MoO4)](2-) and are oriented parallel to the c axis. In the structure, adjacent chains form pseudo-2D-layers parallel to (010). The Cs+ cations are in between the pseudolayers. The composition -structure relationships in alkali metal uranyl molybdates can be rationalized from the viewpoint of dimensional reduction using the following assumptions: (1) representation of the A(x)U(n)Mo(m)O(y) formula (n <= m) as a sum of UMoO6 (= UO2MoO4), A(2)O, and A(2)MoO(4) (A = alkali metal): A(x)U(n)Mo(m)O(y) = kA(2)O + nUMoO(6) + (m-n)A(2)MoO(4), where x = 2(k + m - n) and y = k + 2n + 4m; (2) analysis of the dimensionality of uranyl molybdate structural units and its changes upon incorporation of ionic reagents A(2)O and A(2)MoO(4) into a parent framework Of UO2MoO4 that consists of 3-D array of U and Mo based polyhedra. The relationships between different compositions and structures may be visualized using the UO2MoO4-A(2)O-A(2)MoO(4) compositional diagram. The observed trends of decreasing dimensionality of the uranyl molybdate units allow to specify on this diagram fields of dimensionality.

Document Type: Article
Keywords: uranyl molybdates crystal structures dimensional reduction bond-valence parameters crystal-chemistry se clusters lattice q=s recombination uranium access sheets
Research affiliation: Kiel University > Faculty of Mathematics and Natural Sciences > Institute of Geosciences
DOI etc.: 10.1002/zaac.200700270
ISSN: 0044-2313
Date Deposited: 12 Jan 2012 05:41
Last Modified: 09 Oct 2012 03:56
URI: http://eprints.uni-kiel.de/id/eprint/15557

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