A new class of 30-tungsto polyoxometalates: Preparation, structure, and electrochemical properties of bispyrophosphatotriacontatungstate [(P2O7)2W30O90]8−

The tetrapropylammonium (Pr4N+) salt of [(P2O7)2W30O90]8− was prepared from a 200 mM WVI–10 mM P2O74−–0.5 M HCl–20% (v/v) CH3CN system. The X-ray structural analysis revealed that the [(P2O7)2W30O90]8− anion possessed the same framework as [(P2O7)2Mo30O90]8− isolated by Kortz. The present [(P2O7)2W30O90]8− anion exhibited consecutive one-electron redox waves in neutral CH3CN media, and the one-electron waves were merged into two-electron waves by the presence of H+. These voltammetric properties are entirely different from those of [(P2O7)2Mo30O90]8− that undergoes a two-electron reduction without the aid of H+. The difference in the voltammetric properties can be ascribed to the large pseudo Jahn–Teller (PJT) distortions of MoO6 octahedra in the [(P2O7)2Mo30O90]8− structure.