Mixed-ligand complex formation equilibria of vanadium(III) with 1,10′-Phennanthroline and the amino acids glycine, proline, α-alanine and β-alanine

In this work, we present the results of the speciation of the ternary vanadium(III)-1,10-Phennanthroline(Phen) and the amino acids glycine (HGly), proline (HPro), α-alanine (HαAla) and β-alanine (HβAla) by means of potentiometric measurements in 3.0 mol ∙ dm− 3 KCl 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 and the respective stability constants of the binary complexes and the acid base reactions of the ligands which were kept fixed during the analysis. In the systems studied the complexes [V2O(Phen)(L)]3 +, [V2O(Phen)2(L)2]2 + and V(OH)2(Phen)(L) were observed, where L represents the deprotonated form of the amino acids studied in this work. The qualitative analysis of the spectrophotometric measurements corroborates the oxo-dimer formation in these complexes studied. The respective stability constants were determined and the species distribution diagrams as a function of pH were briefly discussed.