Syntheses and structures determination of new polytungstoarsenates [Na2As2W18U2O72]12- and [MAs2W18U2O72]13- (M = NH4+ and K+)

The isomerically pure title complexes are formed by the reaction of a neutralized (pH 7-7.5) solution of WO42- and HAsO42- with an UO22+ solution in a stoichiometric ratio. Sodium salt [Na2As2W18U2O72](12-), ammonium and potassium salts [Na2W18U2O72] (M NH4+, K+) are synthesized and characterized by elemental analysis. IR. Raman, As and W NMR spectroscopies and single crystal structure analysis. Single-line As-75, five-line W-183 NMR and Raman spectra show that the sodium salt (1) contains an anion of C-i symmetry. The ammonium (2) and potassium (3) salts contain anions it) which the two UO22+ and one ammonium or potassium cation are unsymmetrically sandwiched between two A-AsW9O34 (9-) groups. Each uranium atom adopts a pentagonal-bipyramidal coordination, achieved by three equatorial bonds to one AsW9O349- and two bonds to the other. The anions are converted to H6As2W18O62 in strongly acidic medium. (c) 2006 Elsevier Ltd. All rights reserved.