Stability constants of some lanthanide mixed ligand complexes

Abstract

Stability constants of the mixed ligand complexes of some lanthanides, viz., La(III), Pr(III), Nd(III), Gd(III) and Dy(III) with oxydiacetic acid (ODA), tartaric acid (TRA), malic acid (MEA), iminodiacetic acid (IDA) and glycine (GLY) as ligands have been determined <em>p</em>H-metrically at 25 ± 1°C and at an ionic strength of 0.1mol dm^-3 (KNO₃). A comparison of the values of stability constants of the complexes reveals the order, La(III) < Pr(III) < Nd(III) < Gd(III) < Dy(III) in terms of metal ions, binary < ternary < quaternary in terms of complex species, TRA < MEA in terms of hydroxy acids and IDA < GLY in terms of amino acids. The D log <em>K </em>values are negative for all the ternary and quaternary systems; however, DD log <em>K </em>values are significantly positive. These have been explained in terms of intramolecular hydrophobic ligand-ligand interactions. The stability constant data have been used to study the electrostatic factors involved in the formation of these mixed complexes.