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

Abstract

Isomerically pure complexes of [As2W18Cd4(H2O)2O68]10− and [As2W18Zn2(CdOH2)2O68]10− were synthesized in high yield by self-assembly of and (18 : 2) solution with the stoichiometric ratio of Cd2+ and Zn2+ ions. The complexes were characterized by elemental analysis, IR, Raman, 113Cd NMR spectroscopy, and single crystal structure analysis. Single crystal structure analysis was carried out on (NH4)10[As2W18Cd4(H2O)2O68] · 23H2O which crystallized in the monoclinic system, space group C2/c with a = 23.512(3) Å, b = 12.480(2) Å, c = 30.583(4) Å, β = 95.597(3)°, Z = 4, and V = 8931(2) Å3. The structure consists of two B-AsW9 Keggin moieties linked via a rhomb-like Cd4O14 group leading to a C2h symmetry sandwich-type complex. Double- and single-line 113Cd NMR spectra of [As2W18Cd4(H2O)2O68]10− and [As2W18Zn2(CdOH2)2O68]10−, respectively, confirm C2h symmetry for both anions in solution. Replacement of Cd2+ with Zn2+ in [As2W18Zn4(H2O)2O68]10− takes place only under vigorous conditions.