Stability constants and thermodynamic functions of indium(III) complexes with some organic acids from potentiometric data

Abstract

Potentiometric studies of the complexes of indium(III) with several types of organic compound are reported. The order of decreasing stability for the ligands is thiolactic, thioglycolic, lactic, glycolic, α-alanine and glycine. The stepwise changes in the free energy, enthalpy and entropy values for the complexation are evaluated in an ionic strength of 0·2M (NaClO 4) at 35°C. The results have been correlated with those for the corresponding analagues of succinic and β-substituted propionic acid. The stability of the complexes with the analogues of acetic, propionic and succinic acids decreases for a given acid as the substituted group changes from-SH to-OH to-NH 2. For acids which contain the same substituent group decreasing stability is observed for the analogues of succinic, propionic and acetic acids, the only exception being β-mercapto propionic acid. The thermodynamic values reveal that the complexes are stabilised by positive entropy changes.