NMR and X-ray diffraction studies of the complexation of D-(-)quinic acid with tungsten(VI) and molybdenum(VI)

By using multinuclear (H-1,C-13,O-17,Mo-95,W-183) magnetic resonance spectroscopy (1D and 2D), quinic acid is found to form 2 homologous complexes with both tungsten(VI) and molybdenum(VI), in aqueous solution. Two isomeric 1:2 (metal:ligand) complexes involving the carboxylate and the adjacent OH groups are present in the pH range 2-11. One of the W(VI) complexes with quinic acid, WO2(C7H10O6)(2)(2-) has been isolated in the solid state and characterised by X-ray diffraction, the tungsten atom being six-coordinated in an approximate square bipyramidal geometry. This structure is identical to that proposed for the most stable complex in solution. In the presence of hydrogen peroxide and with both metals, quinic acid forms one 1:1:2 (metal : ligand : peroxide) species, also involving the carboxylate and the adjacent OH groups.