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 determined. 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. When possible, correlations with solid-state structures have been made, although in several cases the structure in the solid state deviates from that observed in aqueous solution. Five coordinate vanadium complexes form when the complex contains chelating hydroxylate and amine functionalities, whereas the coordination of carboxylate groups results in complexes with six-coordinate vanadium. The tetradentate ligands chelate the vanadium center with three or four functionalities. At high pH, four functionalities chelate vanadium when at least one of them is also a carboxylate. Only three functionalities in these ligands are tightly bound to the vanadium in complexes at low pH, while the last functionality is either loosely bound or pendent. The potentially hexadentate ligands form complexes with four functionalities chelating vanadium. An empirical correlation is observed for the V-51 NMR inverse line width at half-height as a function of chemical shift and the coordination around the vanadium. The flexibility and modulation in ligand coordination observed in this work could be important for the function of vanadium in biological systems.