Equilibrium studies on ternary chelates of trivalent metal ions with 2-(2-hydroxyphenyl)benzimidazole, 2-(2-hydroxyphenyl)benzoxazole and other ligands in solution

The pH-inetric equilibrium studies of (1:1:1) ternary chelates, MAL where, M = La III , Pr III , Nd III , Gd III , Dy III and Y III ; L = 2-(2-hydroxyphenyl)benzimidazole and 2-(2-hydroxyphenyl)benzoxazole and A = iminodiacctic acid and nitrilotriacetic acid have been carried out in dioxane-water (50% v/v) medium at 30 °C and 0.1 M (KNO 3 ) ionic strength. The formation constants of binary complexes (ML and ML 2 ) are also determined under similar experimental conditions. The formation constants of the ternary complexes, MAL are evaluated and their relative stabilities compared to the corresponding binary complexes are expressed in terms of the statistical parameter, A log K. Various factors influencing the formation and stability of the ternary chelates are discussed.