Synthesis, structure, and characterization of a new sandwich-type arsenotungstocerate, [As2W18CeO71(H2O)3]12-

The rational synthesis of the new sandwich-type arsenotungstocerate [As2W18Ce3O71(H2O)(3)](12-) is reported for the first time by reaction of the trivacant lacunary species A-alpha-[AsW9O34](9-) with appropriate Ce-IV. The single crystal structure analysis was carried out on K-7(H3O)(5)[AsW18Ce3O71(H2O)(3)].9H(2)O; H39As2Ce3K7O88W18; (2) which crystallizes in triclinic system, space group P1 with a = 11.615(5) Angstrom, b = 17.638(7) Angstrom, c = 19.448(8) Angstrom, alpha = 73.643(7)degrees, beta = 88.799(7)degrees, gamma = 88.078(7)degrees and Z = 2. The anion consists on two lacunary A-alpha-[AsW9O34](9-) Keggin moieties linked via a (H2OCeO)(3) belt leading to a sandwich-type structure. Each cerium atom adopts tri-capped trigonal-prismatic coordination achieved by two terminal oxygen of an edge shared paired of WO6 octahedra to each A-alpha-AsW9O349- moiety and two oxygen from the belt and the cap by one mu(3) - O (As, W-2) to each A-alpha-AsW9O349- moiety and one external water ligand. The Ce - O bond lengths average in CeO6 group, Ce - O(As, W-2) and Ce - O(nW) are 2.300(9), 2.887(3) and 2.682(5) Angstrom, respectively. The acid/base titration curve reveals that the anion has two different titrable protons. (C) 2003 Elsevier B.V. All rights reserved.