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

The reactivity of the [(Mo2O4)-O-v](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)]((Mo2O4)-O-v)(2)(O3P(C(CH3)O)-PO3)(2)]center dot 12H(2)O (1) revealed that the hydroxo group of the etidronate ligand can be deprotonated in presence of Mo-v even in acidic media. It follows that its coordination mode thus differs from that of the methylenediphosphonate ligand [O(0)3P(CH2)PO3]4-, which reactivity with Mo-v has been previously widely studied. In contrast, no such deprotonation of the hydroxo group is observed in the (NH4)(18)[((Mo2O4)-O-v)(6)(OH)(6)(O3P(C(CH3)(OH))-PO3)(6)]center dot 35H(2)O complex 2. This species contains a dodecanuclear core analogous to the one previously found in the [((Mo2O4)-O-v)(6)(OH)(6)(O3PCH2PO3)(6)](18-) methylenediphosphonato polyanion. In 2, six interconnected (( (Mo2O4)-O-v)(O3P(C(CH3)(OH))PO3)) units form a cyclohexane-like ring in a chair conformation. In the (CN(3)H(1)6)(18)Na-3{((Mo2O4)-O-v)(7)(O3P (C(CH3)(OH))PO3)(7)(CH3COO)(7)]center dot 5CH(3)COONa 52H(2)O compound 3, seven aMo(2)(v)O(4))(O3P (C(CH3)(OH))PO3)(CH3COO)} units are connected, forming an almost planar tetradecanuclear wheel. This compound represents the largest homometallic Mo-v polyoxometalate cyclic system reported to date. Finally, P-31 NMR studies revealed that only complex 1 is stable in aqueous solution. (C) 2009 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.