Ternary Complexs: Equilibrium Studies of Mixed-ligand Complexes of Neodymium Ion with Carboxylic and Phenolic Acids in Aqueous Medium

Abstract

Abstract The stability constants of simple and mixed ligand systems of neodymium ion with bidentate ligands such as carboxylic and phenolic acids are studied in an aqueous medium by pH metric titrations at 30±0.1 °C and at an ionic strength of 0.1 M (NaClO4). Neodymium forms 1 : 1 complexes with succinic, adipic, itaconic, malonic, and 3,5-dinitrosalicylic acids and 1 : 1 and 1 : 2 complexes with phthalic, 5-sulfo-, and 4-hydroxysalicylic acids. Ternary complexes of neodymium with these acids when (i) both the ligands are carboxylic acids, (ii) one is carboxylic and the other a phenolic acid, (iii) both ligands are phenolic acids, are studied by potentiometry. The stability constants of these complexes are compared with those of binary complexes. The results have been discussed on the basis of the magnitudes of ΔlogK, KDXY, and logβXY−1⁄2[logβxx+logβyy], and also from the comparison of K2YX and KMX1 or K2XY and KMY1. The values of K2YX are directly related to the acid dissociation constant of the secondary ligand. The overall stability (βXY) is found to be depending on the binary stabilities and the basicities of the ligands.