Abstract The isomerically pure title complexes are formed by the reaction of a neutralized (pH 7–7.5) solution of WO4 2 and HAsO4 2 with an UO2 2þ solution in a stoichiometric ratio. Sodium salt [Na2As2W18U2O72]12, ammonium and potassium salts [MAs2W18U2O72]13 ðM ¼ NH4þ;KþÞ are synthesized and characterized by elemental analysis, IR, Raman, As and W NMR spectroscopies and single crystal structure analysis. Single-line 75As, five-line 183W NMR and Raman spectra show that the sodium salt (1) contains an anion of Ci symmetry. The ammonium (2) and potassium (3) salts contain anions in which the two UO2 2þ and one ammonium or potassium cation are unsymmetrically sandwiched between two A-AsW9O34 9groups. Each uranium atom adopts a pentagonal-bipyramidal coordination, achieved by three equatorial bonds to one AsW9O34 9 and two bonds to the other. The anions are converted to H6As2W18O62 in strongly acidic medium.  2006 Elsevier Ltd. All rights reserved.

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