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

Abstract

Multinuclear ( 1H, 13C, 17O, 31P, 95Mo, 183W) 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 2O 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 2O 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.