Synthesis, Stability, and Crystal Structure of the (NMe2H2)9[(AsW9O33)2(NbO)3(H2O)]·44H2O Complex

Abstract

Citrate complexes of niobium(V) formed in the interaction of [Nb6O19]8− hexaniobate with citric acid are used for transferring the {NbO}3+ niobium group to the pseudo-trilacunary [α-B-AsIIIW9O33]9− anion with the formation of sandwich-type [(AsW9O33)2(NbO)3(H2O)]9− complexes. Slow evaporation of the reaction mixture in the presence of dimethylammonium chloride yields crystalline product (NMe2H2)9[(AsW9O33)2(NbO)3(H2O)]·44H2O (1) whose structure is determined by single crystal XRD. When the (NBu4)+ salt (obtained by the exchange reaction between 1 and tetrabutylammonium bromide) of [(AsW9O33)2(NbO)3(H2O)]9− is dissolved in DMF, As3+ is oxidized to As5+ with the formation of a mixture of the Keggin-type [AsW11NbO40]4− and [AsW10Nb2O40]5− anions. In an aqueous solution 1 is oxidized by hydrogen peroxide with the formation of a mixture of Keggin anions with different numbers of niobium atoms in the structure.