Thermodynamics of binary and ternary complexes of 3-amino-1,2,4-triazole and amino acids with Ni(II) and Co(II) metal ions

Abstract

The stability constants of the 1:1 binary complexes of Ni(II) and Co(II) with 3-amino-1,2,4-triazole (AT), leucine (Leu) and glutamic acid (Glu), and the 1:1:1 ternary complex of them and the protonation constants of the ligands were determined potentiometrically at a constant ionic strenoth of I = 0.10 mol L-1 (NaClO4) in aqueous Solutions at 15.0 and 25.0 degrees C. The thermodynamic parameters Delta G(f)(0), Delta H-f(0) and Delta S-f(0) are reported for the formation reactions of the complexes. The enthalpy changes of all the complexations were found to be negative but the entropy changes positive. While the driving force for the formation of the Ni(II), Co(II) - AT complexes is the enthalpy decrease, the driving force for the ternary complexes of AT is the entropy increase.