Peroxo complexes of sugar acids with oxoions of Mo-VI and W-VI as studied by NMR spectroscopy

By using multinuclear H-1, C-13, O-17, Mo-95 and W-183 magnetic resonance spectroscopy (1-D and 2-D), aldonic acids, alduronic acids and aldaric acids have been found respectively to form one, four and three homologous oxoperoxo complexes with Mo-VI and W-VI, in aqueous solution (pH range 2-11). Common features are the involvement of two peroxide units per metal centre and the co-ordination of the sugar acids through carboxylate and adjacent hydroxyl groups. Accordingly, 1:1:2 (metal:acid:peroxide) complexes are detected as well as 2:1:4 species in the case of the aldaric acids. The geometry around each MO4+ centre is approximately pentagonal bipyramidal, the M=O group occupying one of the apical positions and the two peroxo ligands being equatorial. The sugar acid is co-ordinated in one equatorial and in one apical site.