Multinuclear NMR study of the complexes of 6-phospho-D-gluconic acid with W(VI) and Mo(VI).

Multinuclear ((1)H, (13)C, (17)O, (31)P, (95)Mo, (183)W) magnetic resonance spectroscopy (1D and 2D) has been used to show that 6-phospho-d-gluconic acid forms three complexes with tungsten(VI) and six complexes with molybdenum(VI) in aqueous solution, depending on pH and concentration. Two isomeric 1:2 (metal-ligand) complexes are detected both with tungstate(VI) and molybdate(VI), having MO(2)(2+) centres and involving the carboxylate and the adjacent OH groups in addition to one 2:1 (metal-ligand) complex possessing a M(2)O(5)(2+) centre, with the ligand being coordinated by the carboxylate group and the three consecutive OH groups in positions 2, 3 and 4. Molybdate(VI) forms three additional species, which are not detected with tungstate. One of them is a 2:1 complex with a Mo(2)O(5)(2+) centre, with the ligand being tetradentate via O-3, O-4, O-5 and the phosphate group. The other two are 12:4 species, which can be seen as two 1:2 complexes bound together in a ring through two diphosphomolybdate moieties each derived from heptamolybdate by inclusion of two phosphate groups from the ligands.