Equilibrium Studies on Some Lanthanide(III) Complexes with Oxine as Primary Ligand and Vitamin U as Secondary Ligand and Its Comparison with Binary Complexes

Abstract

The formation constants of the mixed ligand complexes at 1 : 1 : 1 optimum molar concentration of metals such as La(III), Pr(III), Sm(III) and Gd(III) as primary ligand, A = oxine and N–O donor atoms as secondary ligand, L = vitamin U have been determined by modified form of Irving-Rossotti titration technique in aqueous media at constant ionic strength (μ = 0.2 M dm^–3) at 25 ± 0.1 °C. The difference between the stability of ternary complexes and the corresponding binary complexes has been expressed in terms of parameter D log K_T. The stabilities of the ternary complexes are explained in terms of p-basicities, structures of secondary ligand and ring size of chelate. D log K_T values are negative which suggest favourable formation of ternary complexes. The D log K_T values have been explained in terms of M®L, p-interaction, size of the chelate ring and factors from metal side.