CHARACTERIZATION OF VANADIUM(V) COMPLEXES IN AQUEOUS-SOLUTIONS - ETHANOLAMINE-DERIVED AND GLYCINE-DERIVED COMPLEXES

The preferred coordination geometry of vanadium(V) in aqueous solution with nitrogen- and oxygen-containing multidentate ligands has been de termined. The ligands all contain at least two oxygen functionalities and one amine functionality and are derived from diethanolamine (DEA), glycine, and ethylenediaminetetraacetic acid (EDTA). The complexes of 17 ligands have been examined using a combination of H-1, (1)3C, V-51 , and O-17 NMR spectroscopy and IR and UV-vis spectrophotometries. Whe n possible, correlations with solid-state structures have been made, a lthough in several cases the structure in the solid state deviates fro m that observed in aqueous solution. Five coordinate vanadium complexe s form when the complex contains chelating hydroxylate and amine funct ionalities, whereas the coordination of carboxylate groups results in complexes with six-coordinate vanadium. The tetradentate ligands chela te the vanadium center with three or four functionalities. At high pH, four functionalities chelate vanadium when at least one of them is al so a carboxylate. Only three functionalities in these ligands are tigh tly bound to the vanadium in complexes at low pH, while the last funct ionality is either loosely bound or pendent. The potentially hexadenta te ligands form complexes with four functionalities chelating vanadium . An empirical correlation is observed for the V-51 NMR inverse line w idth at half-height as a function of chemical shift and the coordinati on around the vanadium. The flexibility and modulation in ligand coord ination observed in this work could be important for the function of v anadium in biological systems.