Determination of the thermodynamic parameters and stability constants of UO22+, Th4+, and Ce3+ complexes with some azo-benzene-N-malonic acid derivatives

Proton-ligand dissociation and metal-ligand formation constants of azobenze ne-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 UO22, Th4+ and Ce3+ were evaluated potentiometrically using Bjerrum's method at 25,35 and 45 +/-0.5 degreesC and ionic strength 0.1 M in 40% v/v ethanol-w ater medium. The order of stability constants was found to be Ce3+ > Th4+ > UO22+. The effect of temperature on the dissociation and stability constan ts of the formed complexes was studied and the corresponding thermodynan-dc functions were derived and discussed. The ratio of metal-ligand was determ ined conductometrically. The structure of the ligands under investigation a s well as their metal complexes has been elucidated by elemental analysis, IR and H-1(NMR) spectroscopy.