Synthesis and characterization of Cs(5)P[Mo(4)O(14)(OH)](2).2H(2)O: a new molybdophosphate cluster with face-sharing MoO(6) octahedra.

Within the ever-growing field of (hetero)polyoxometalates, the molybdophosphate system occupies a special place as being one of the most extensively studied and quite well understood systems. Its speciation in aqueous solution as a function of pH and phosphate concentration has been established precisely by various methods such as potentiometric, NMR, Raman, and cyclic voltammetry measurements.1 The predominant species in such solutions include [HxP2Mo5O23]; the well-known Keggin ion [PMo12O40] and its lacunary derivatives [HxPMo9O34], [HxPMo10O37], and [HxPMo11O39]; and the WellsDawson ion [P2Mo18O62], all built of MoO6 octahedra sharing corners and/or edges and connected by PO4 tetrahedra.1 Reported here is a new molybdophosphate, Cs5P[Mo4O14(OH)]2‚2H2O (1), with two {Mo4O14(OH)} fragments connected by a phosphate group. The {Mo4O14(OH)} fragment, identified for the first time in a molybdophosphate species, contains MoO6 octahedra sharing edges and, quite unusual for (hetero)polyoxomolybdates, faces.