Synthesis, Structure, and Characterization of an α-Dawson-type [S2W18O62]4− Complex

A yellow sulfatotungstate complex was formed by heating a 50 mM W(VI)–2 M H2SO4–40% (v/v) CH3CN system at 70 °C for 14 days, being isolated as the tetrapropylammonium (n-Pr4N+) salt. An X-ray structural analysis (ortho-rhombic, Pca21 (No. 29) a = 27.181(1), b = 14.1428(6), c = 27.7292(9) A, and Z = 4) revealed that the structure consists of an α-Dawson-type [S2W18O62]4− anion. The α-[S2W18O62]4− complex underwent a four-step reversible one-electron reduction in CH3CN, and the presence of acid caused the one-electron waves to be converted into three two-electron waves. The formation conditions were elucidated by a combined Raman and voltammetric study.