Potentiometric Investigation on Complexation of Divalent Transition Metal Ions with Some Zwitterionic Buffers and Triazoles

Abstract

The interaction between the zwitterionic buffers N-(2-acetamido)iminodiacetic acid (ADA), N-[tris(hydroxymethyl)methyl]glycine (tricine), and N,N-bis(2-hydroxyethyl)glycine (bicine) and 1,2,4-triazole (TRZ), 3-mercapto-1,2,4-triazole (TRZSH), and 3-amino-1,2,4-triazole (TRZAM) with the divalent transition metal ions, Cu2+, Ni2+, Zn2+, and Co2+, was investigated in aqueous media at 25 °C and ionic strength I = 0.1 mol·dm−3 NaNO3 using the potentiometric technique. The acid−base properties of the ligands were investigated and discussed. The acidity constants of the ligands were determined and used for determining the stability constants of the different complexes formed in solution. The formation of the different 1:1 and 1:2 binary complexes and 1:1:1 ternary complexes is inferred from the corresponding titration curves. The ternary complex formation was found to occur in a stepwise manner. The order of stability of the complexes formed in solution was investigated in terms of the nature of the zwitterionic buffer, triazole, and metal ion used. The values of Δlog K, percentage of relative stabilization (% R.S.), and log X for the mixed-ligand complexes studied have been evaluated and discussed. The concentration distribution of the various species formed in solution was evaluated. The ionization processes of ADA and TRZAM and their interaction with Cu2+, Ni2+, and Co2+ were studied at different temperatures [(15, 25, 35, and 45) °C], and the corresponding thermodynamic parameters have been evaluated and discussed. In addition, the dissociation constants of ADA and TRZAM and stability constants of their 1:1 binary and 1:1:1 ternary complexes with Ni2+ in various water + dioxane mixtures at 25 °C were determined and discussed.