Synthesis and structure of sandwich-type polytungstoarsenates of [As2W18Cd4(H2O)2O68]10- and [As2W18Zn2(CdOH2)2O68]10-

Isomerically pure complexes of [As2W18Cd4(H2O)(2)O-68](10-) and [As2W18Zn2(CdOH2)(2)O-68](10-) were synthesized in high yield by self-assembly of WO42- and HAsO42- (18 : 2) solution with the stoichiometric ratio of Cd2+ and Zn2+ ions. The complexes were characterized by elemental analysis, IR, Raman, Cd-113 NMR spectroscopy, and single crystal structure analysis. Single crystal structure analysis was carried out on (NH4)(10)[As2W18Cd4(H2O)(2)O-68] center dot 23H(2)O which crystallized in the monoclinic system, space group C2/c with a = 23.512(3) angstrom, b = 12.480(2) angstrom, c = 30.583(4) angstrom, beta = 95.597(3)degrees, Z = 4, and V = 8931(2) angstrom 3. The structure consists of two B-AsW9O349- Keggin moieties linked via a rhomb-like Cd4O14 group leading to a C-2h symmetry sandwich-type complex. Double-and single-line Cd-113 NMR spectra of [As2W18Cd4(H2O)(2)O-68](10-) and [As2W18Zn2(CdOH2)(2)O-68](10-), respectively, confirm C-2h symmetry for both anions in solution. Replacement of Cd2+ with Zn2+ in [As2W18Zn4(H2O)(2)O-68](10-) takes place only under vigorous conditions.