NMR spectroscopy study of the complexation of d-gluconic acid with tungsten(VI) and molybdenum(VI)

By using multinuclear (1H, 13C, 17O, 95Mo, 183W) magnetic resonance spectroscopy (1D and 2D), d-gluconic acid is found to form 10 and 8 complexes, respectively, with tungsten(VI) and molybdenum(VI) in aqueous solution, depending on pH and concentration conditions. Two isomeric 1:2 (metal:ligand) complexes involving the carboxylate and the adjacent OH group and one 2:1 complex, involving the carboxylate group and three OH groups are present in the whole pH range covered (2–11). At high pH, three 2:1 complexes are detected, each one involving four hydroxyl groups of the ligand. At intermediate pH values, two additional 5:2 isomeric complexes are found involving the carboxylate group and all the hydroxyl groups. Tungsten(VI) in alkaline medium is also able to form two additional (tetradentate and tridentate) 2:1 species.