Effect of ring size due to secondary ligand on the stability of some ternary lanthanide complexes

The present work describes the effect of the size of ring formed by the secondary ligand on the stability of the ternary mixed ligand complex of the type LN-EDTA-L, where LN=La3+, Ce3+, Pr3+, Nd3+, Sm3+, EDTA=A=primary ligand and L=secondary ligand (malonate, succinate or glutarate). The combination of lanthanides in the complexes of which the l.f.s.e. is very low and the saturated dicarboxylic acids, which form symmetrical rings, is considered appropriate for studying the effect of ring size on the stability of the mixed complexes. A pair of isomeric alanines (α and β) has also been used where the α-isomer forms a five membered ring and the β-isomer a six membered ring. (author)