Characterization of tetra, dodeca and tetradeca MoV polyoxometalate wheels structured by etidronate ligands

Abstract

Abstract The reactivity of the [MoV2O4]2+ dinuclear unit with the [O3P(C(CH3)(OH))PO3]4− etidronate ligand has been investigated. Three complexes have been isolated and characterized by IR spectroscopy, elemental analysis and single crystal X-Ray diffraction studies. Structural determination of the tetranuclear compound (CN3H6)6[(MoV2O4)2(O3P(C(CH3)O)PO3)2]·12H2O (1) revealed that the hydroxo group of the etidronate ligand can be deprotonated in presence of MoV even in acidic media. It follows that its coordination mode thus differs from that of the methylenediphosphonate ligand [O3P(CH2)PO3]4−, which reactivity with MoV has been previously widely studied. In contrast, no such deprotonation of the hydroxo group is observed in the (NH4)18[(MoV2O4)6(OH)6(O3P(C(CH3)(OH))PO3)6]·35H2O complex 2. This species contains a dodecanuclear core analogous to the one previously found in the [(MoV2O4)6(OH)6(O3PCH2PO3)6]18− methylenediphosphonato polyanion. In 2, six interconnected {(MoV2O4)(O3P(C(CH3)(OH))PO3)} units form a cyclohexane-like ring in a chair conformation. In the (CN3H6)18Na3[(MoV2O4)7(O3P(C(CH3)(OH))PO3)7(CH3COO)7]·5CH3COONa 52H2O compound 3, seven {(MoV2O4)(O3P(C(CH3)(OH))PO3)(CH3COO)} units are connected, forming an almost planar tetradecanuclear wheel. This compound represents the largest homometallic MoV polyoxometalate cyclic system reported to date. Finally, 31P NMR studies revealed that only complex 1 is stable in aqueous solution.