Formation and stability of transition metal chelates with 2-(2-hydroxyphenyl) benzoxazole and other ligands

The formation equilibria of (1 : 1 and 1 : 2) binary chelates, ML and ML 2 and (1 : 1 : 1) ternary chelates, MAL where, M = Co", Ni ΙΙ and Zn"; L = 2-(2-hydroxyphenyl)benzoxazole (HPBO) and A = glycine, alanine, proline and histidine have been studied pH-metrically in aqueous-dioxane (50% v/v) medium at 30 °C and 0.1 M (KNO 3 ) ionic strength. The formation constants of the complexes were evaluated. The relative stabilities of the ternary complexes were expressed in tenns of the parameter Alog K and various factors influencing the formation and stability of complexes are discussed. The thermodynamic parameters (AH, AS and AG) associated with the ternary systems were also evaluated by determining the formation constants at 20, 30 and 40 °C and 0.1 M KNO 3 ionic strength. All the parameters were found to be favourable for the complexation.