Vanadium(V) complexes of alpha-hydroxycarboxylic acids in aqueous solution

V-51 NMR and IR spectroscopic studies of the complexes formed between vanad ate and the alpha -hydroxylic acid ligands, (S)-2-hydroxypropanoic acid (L- (+)-lactic acid), 2-hydroxy-2-methylpropanoic Acid, and 2-ethyl-2-hydroxybu tanoic acid were carried out for aqueous 1 M ionic strength (NaCl) solution s. Three major products in V to L stoichiometries of 1:1, 2:2, and 3:2 were identified from vanadate and ligand concentration studies, while a pH vari ation study allowed charge states to be determined. At pH 7.06, the formati on constants for the predominant reactions were (26 +/- 1) M-1, (V + L reve rsible arrow VL); (6.8 +/- 0.4) x 10(3) M-1, (2VL reversible arrow V2L2); a nd (3.5 +/- 0.3) x 10(3) M-1, (V2L2 + V reversible arrow V3L2). Dissolution studies of various crystalline products were carried out for aqueous, nona queous, and mixed solvent systems. These studies combined with information available from X-ray structural studies provided a basis for the assignment of solution state structures. Pentacoordinate vanadium in a trigonal-bipyr amidal geometry was proposed for the both the 1:1 and 2:2 complexes when in aqueous solution. Observed changes in V-51 chemical shift patterns were co nsistent with a cis fusion in octahedral coordination for the central vanad ium of the 3:2 complex, while the remaining vanadiums retained a pentacoord inate geometry.