Synthesis and characterization of [Mo7O16(O3PCH2PO3)3]:8- -: A mixed-valent polyoxomolybdenum diphosphonate anion with octahedrally and tetrahedrally coordinated molybdenum

Two new compounds containing the title diphosphono-polyoxometalate anion and diprotonated ethylenediamine (enH(2)) or piperazine (ppzH(2)) countercations have been hydrothermally synthesized and structurally characterized ((enH(2))(4)[Mo7O16(O3PCH2PO3)(3)].7H(2)O, triclinic, P (1) over bar, Z = 2, a = 10.3455(7) Angstrom, b = 13.136(1) Angstrom, and c = 20.216(3) Angstrom, alpha = 93.247(6)degrees, beta = 96.434(6)degrees, and gamma = 111.900(6)degrees; (ppzH(2))(4)[Mo7O16(O3PCH2PO3)(3)](.)8H(2)O, triclinic, P (1) over bar, Z = 2, a = 13.255(2) Angstrom, b = 13.638(2) Angstrom, and c = 16.874(4) Angstrom, alpha = 93.20(2)degrees, beta = 101.27(2)degrees, and gamma = 105.87(1)degrees). The anion is a ring of three pairs of edge-sharing octahedra of (MoO6)-O-V (with Mo-V-Mo-V bonds) that share corners with each other. The cliphosphonate groups connect the pairs at the periphery. The ring is capped by a tetrahedron of (MoO4)-O-VI. According to magnetic measurements, the compounds are diamagnetic.