Studies of some lanthanide quaternary complexes

Formation constants of mixed ligand quaternary lanthanide complexes of the type M-A-B-L'/L' where M=La3+, Pr3+, Nd3+; A=ethylenediamine N, N, N', N'-tetraacetic acid (EDTA); B=thiodiglycolic acid (TDA); L'=iminodiacetic acid (IDA) and L'=glycine (GLY) have been determined by pH-metric technique at 35±1degC in 0.1 mol dm-3KNO3. Stability constants reveal the orders: La(III)<Pr(III)<Nd(III) in terms of metal ions, binary<ternary<quaternary in terms of complex species, and IDA<Gly in terms of amino acids. The Δ LOG K values are negative for all the ternary and quaternary systems. However, Δ log K values are significantly positive indicating intramolecular hydrophobic ligand-ligand interactions. (author). 16 refs