Preparation and characterization of an α-Keggin-type [SW12O40]2- complex

A divanadium-substituted derivative of 12-tungstosulfaten(VI), [S(V 2 W 1 0 )O 4 0 ] 4 - was prepared as the tetrabutylammonium (n-Bu 4 N + ) salt by heating a 50 mM (M = mol dm - 3 ) W(VI)-20 mM V(V)-0.5 M H 2 SO 4 -50% (v/v) CH 3 CN system at 70 C for 24 h. The [S(V 2 W 1 0 )O 4 0 ] 4 - anion was transformed spontaneously into a monovanadium-substituted derivative, [S(VW 1 1 )O 4 0 ] 3 - in a 70% (v/v) CH 3 CN-1.0 M HCl system at 70 C. On the other hand, [SW 1 2 O 4 0 ] 2 - was precipitated as the n-Bu 4 N + salt upon heating a 95% (v/v) CH 3 CN-0.5 M HCl system containing [S(V 2 W 1 0 )O 4 0 ] 4 - . The single-crystal X-ray structural analysis revealed that the structure consisted of an α-Keggin-type [SW 1 2 O 4 0 ] 2 - anion. The [SW 1 2 O 4 0 ] 2 - anion was characterized by IR and UV-vis spectroscopy, and voltammetry.