A bicapped, highly reduced vanadylpolymolybdophosphate Keggin complex [(C2H5)(3)NH](5)[(PMo6Mo6O40)-Mo-V-O-VI-((VO)-O-IV)(2)], (TEA) 1, has been prepared hydrothermally and characterized by single-crystal X-ray diffraction, LR, UV/visible, cyclic voltammetry, elemental analysis, redox titration, and V-51 and P-31 NMR on its degradation products. The kinetics of decomposition of 1 in aqueous solution under both aerobic and anaerobic conditions is complex.