A 13C and 183W NMR study of the structures of tungstate and molybdate complexes of volemitol

1H, 13C, and 183W NMR spectroscopic methods were used for the structural characterization of the tungstate and molybdate complexes of volemitol (d-glycero-d-manno-hepitol) in aqueous solution. The major species (type E) are a pair of isomeric complexes formed at the arabino site in reversed orientation, i.e., HO-1,2,3,4 and HO-4,3,2,1. A single, minor complex is formed at the HO-3,4,5,6 altro site and is shown to be isostructural with the known single complexes of ribitol and d-altritol (type E′). The present NMR results support the hypothesis that complexes of type E′ are weaker than those of type E because they are destabilized by a steric strain due to the interaction of the side chain of the ligand with the site of chelation.