Fluorine Tagging of Polyoxometalates: The Cyclic [{MoV2O4(H2O)}4{O3PC(CF3)(O)PO3}4]12-

We have discovered a simple and efficient strategy to incorporate fluorine into polyoxometalates by reaction of the fluorinated diphosphonate H2O3PC(CF3)(OH)PO3H2 with [(Mo2O4)-O-V(H2O)(6)](2+) in aqueous medium (pH = 6.4) resulting in [{(Mo2O4)-O-V(H2O)}(4) {O3PC(CF3)(O)PO3}(4)](12-) (1), which was structurally characterized in solution by multinuclear NMR spectroscopy and in the solid state by single-crystal X-ray diffraction, infrared, thermogravimetric and elemental analyses. Polyanion 1 crystallizes as the mixed sodium/guanidinium salt Na-6.5[(H2N)(3)C](5.5)[{(Mo2O4)-O-V(H2O)}(4){O3PC(CF3)(O)-PO3}(4)]center dot 8H(2)O (la) in the monoclinic system, space group C2/c with the unit-cell parameters a = 34.0685(95) angstrom, b = 8.0874(19) angstrom, c = 34.4101(10) angstrom, beta = 100.20(2)degrees, V = 9331.02(4) angstrom(3) and Z = 2. The novel polyanion 1 has a cyclic, saddle-like structure with four {Mo2O4(H2O)} units linked by four fully deprotonated diphosphonate moieties. In addition, the (CF3)C-OH moiety is deprotonated, due to the electronic effects of the neighboring CF3 group, leading to the formation of an Mo-O(C) bond. Solution P-31 and F-19 NMR studies of 1 indicate magnetic inequivalence of the two phosphorus atoms in each diphosphonate moiety. The solid-state packing of the title polyanions in la by loosely bound Na+ counterions leads to an AAA-type arrangement.