[e-PMo12O36(OH)4{La(H2O)4}4]5+: The First e-PMo12O40 Keggin Ion and Its Association with the Two-Electron-Reduced α-PMo12O40 Isomer

Six Mo dimers arranged around a central PO4 tetrahedron form the core of the novel ε-Keggin polyoxocation [ε-PMo12O36(OH)4{La(H2O)4}4]5+ (see structure) capped with four {La(H2O)4}3+ units. A 31P NMR spectroscopy study shows that the ε-Keggin ion is unstable in aqueous solution, and leads to the formation of a polyanion/polycation salt, which is crystallographically characterized.