Study of ternary complex formation in solution at different temperature and ionic strengths by potentiometric method

Abstract

In the field of mixed ligand complexing equilibria in solution a remarkable interest has been observed in the researchers these days. Chelates of mixed ligand are known to play an vital role in the various fields e.g. analytical, medicinal, environmental, industrial chemistry and also help in understanding several biological process. In the present thesis several binary and ternary complex formation equilibria with trivalent rare earth element ions viz Tb(III), Dy(III), Ho(III), and Er(III) involving CDTA, IMDA and several other ligands such as valine, leucine, serine, phenylalanine, tyrosine, tryptophan, threonine, glutamine and asparagine are reported. The Studies have been performed at different temperatures [viz, 25, 35 and 45°C] and different ionic strengths [viz, 0.15 M, 0.10 M and 0.05 M (KNO3)] and extrapolated to zero ionic strength in order to evaluate the thermodynamic stability constant. The displacement of the experimental mixed ligand titration curves from the theoretical composite curve, and non-appearance of turbidity/opacity provides the evidence for the formation of mixed ligand complex. The formation of mixed ligand complex takes place by two ways 1. Stepwise addition of two ligands to the metal ions and, 2. Simultaneous addition of two ligands to the metal ions. The nature of complex equilibrium whether it is stepwise or simultaneous by Martell and Carey s method. The values of proton dissociation constant of the various ligands and the metal ligand formation constant of all the binary complexes are calculated by Martell and Chaberek method as modified by Dey et al., Thompson and Lorass method has been used to evaluate the formation constants of the mixed ligand complexes involving stepwise equilibria, while Ramamoorthy and Santappa has been used to evaluate the formation constants of the mixed ligand complexes involving simultaneous coordination of two ligand L and L to the metal ions. The theoretical details of all these methods are described in chapter - I of the thesis.