Stability parameters of some lanthanide mixed ligand complexes

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±1degC 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, ΔΔ log K values are significantly positive. It shows the intramolecular hydrophobic ligand interaction. (author). 27 refs., 2 figs., 4 tabs