Determination of the thermodynamic parameters and stability constants of UO2(2+), Th4+, and Ce3+ complexes with some azo-benzene-N-malonic acid derivatives.

Proton-ligand dissociation and metal-ligand formation constants of azobenzene-N-malonic acid (I), p-Cl-azobenzene-N-malonic acid (II), p-Br-azobenzene-N-malonic acid (III) and p-COOH- azobenzene-N-malonic acid (IV) with UO2(2+), Th4+ and Ce3+ were evaluated potentiometrically using Bjerrum's method at 25, 35 and 45 +/- 0.5 degrees C and ionic strength 0.1 M in 40% v/v ethanol-water medium. The order of stability constants was found to be Ce3+ > Th4+ > UO2(2+). The effect of temperature on the dissociation and stability constants of the formed complexes was studied and the corresponding thermodynamic functions were derived and discussed. The ratio of metal-ligand was determined conductometrically. The structure of the ligands under investigation as well as their metal complexes has been elucidated by elemental analysis, IR and 1HNMR spectroscopy.