Dielectric constant dependence of formation constants: Complexation of dioxovanadium(V) with methionine

The reaction of dioxovanadium(V) with methionine was studied by spectrophotometric titrations in mixed solvent systems of methanol + water and dioxane + water at 25degreesC and constant ionic strength 0.15 mol l(-3) NaClO(4) in the pH range 1.5-8, with high ligand to metal ratios. Two mononuclear complexes ML and ML(2) have been characterized for the ligands. The stability constants of the complexes formed and their stoichiometries are given and interpreted. Linear relationships are observed when logbeta is plotted versus 1/D, where beta and D represent formation and dielectric constants, respectively. The results are discussed in terms of the effect of the solvent on protonation and complexation.