Equilibrium studies of mixed-ligand complexes of uranyl ion with carboxylic acids in aqueous solution

Abstract

Equilibrium studies on mixed-ligand complexes of uranyl ion with carboxylic acids, malonic, diglycollic, maleic, crotonic, glycollic, thioglycollic and mercaptopropionic, as ligands were carried out by the pH titration method at 31 ± 0·1°C and ionic strength μ = 0·1 mol dm −3 (NaClO 4). Different equilibrium constants, characteristic of mixed-ligand complexes were calculated. In most of the systems studied, ternary complexes were found to be more stable than the corresponding binary complexes. The stabilities of ternary complexes appear to depend on the size of the chelate ring; the difference in stabilities of 1:1 and 1:2 binary complexes; the nature of the donor atom and the charge neutralization if any. In general, the stability is attributed to the unsymmetrical nature of the ternary complex.