Mixed-Ligand Complex Formation Equilibria of Vanadium(III) with 2,2′-Bipyridine and the Amino Acids Glycine, Proline, α-Alanine and β-Alanine Studied in 3.0 mol⋅dm−3 KCl at 25 °C

Abstract

We studied speciation of the mixed-ligand complex formation equilibria of vanadium(III) with both 2,2′-bipyridine (Bipy) and the amino acids glycine (HGly), proline (HPro), α-alanine (HαAla), and β-alanine (HβAla) by means of electromotive forces measurements emf(H) using 3.0 mol⋅dm−3 KCl as the ionic medium at 25 °C. The experimental data were analyzed by means of the computational least-squares program LETAGROP, taking into account the hydrolysis of the vanadium(III) cation, the respective stability constants of the binary complexes, and the acid/base reactions of the ligands which were kept fixed during the analysis. In all four amino acid systems studied we observed the complexes [V2O(Bipy)(B)]3+, [V2O(Bipy)2(B)2]2+, [V(OH)(Bipy)(B)2] and [V(OH)2(Bipy)(B)], where B represents the deprotonated form of the amino acids studied in this work. The respective stability constants were determined and the species distribution diagrams as a function of pH are briefly discussed.