Stability Parameters of Some lanthanide Mixed Ligand Complexes

Abstract

Stability constants of mixed ligand complexes of lanthanide metal ions viz. La(III), Pr(III) and Nd(III) with ethylene diamine-N,N,N´,N´-tetra-acetic acid (EDTA), pyridine-2,6-dicarboxylic acid (PDA), iminodiacetic acid (IDA) and glycine (GLY) as ligand have been studied potentiometrically at temperature 25±1ºC and ionic strength 0.1 mol dm^–3 KNO₃. A comparison of the stability constants in binary, ternary and quaternary complexes reveal the order, La(III) < Pr(III) < Nd(III) in terms of metal ions, binary < ternary < quaternary in terms of complex species and IDA < GLY in case of amino acids. The Δ log K values are negative for all the ternary and quaternary systems, however, Δ Δ log K values are significantly positive. It shows the intramolecular hydrophobic ligand interaction.