Carbohydrate-Metal ComplexesCarbohydrate–metal complexes : Structural Chemistry of Stable Solution Species

Abstract

This review discusses the structural chemistry of metal complexes of carbohydrates and their derivatives with the focus on crystal structure and NMR data of stable solution species. There is evidence that the stability of these complexes is markedly increased when the carbohydrates operate as chelating polyolato ligands, this is, when they are multiply deprotonated polydentate ligands. The 1,2-diolato coordination mode resulting in five-membered chelate rings is most commonly observed. Small torsion angles within the 1,2-diolato moiety enable the chelation of small atoms while larger torsion angles are usually needed for the complexation of large atoms. Hence, as a consequence of the limited flexibility of the pyranose ring, pyranoidic 1,2-diols merely form less-stable complexes with small metal centers in marked contrast to furanoidic 1,2-diols. An additional contribution to the stability arises from hydrogen bonds, especially intramolecular ones, with the deprotonated ligator oxygen atoms acting as strong hydrogen-bond acceptors.