COMPLEXATION THERMODYNAMICS OF LANTHANIDE IONS BY BENZENEPOLYCARBOXYLATE LIGANDS

The complexation thermodynamics of lanthanide ions by 1,2,3-benzenetri carboxylate (hemimellitate), 1,2,4-benzenetricarboxylate (trimellitate ) and 1,2,4,5-benzenetetracarboxylate (pyromellitate) ligands were stu died using potentiometric, calorimetric and extraction techniques. The measurements were obtained at an ionic strength of 0.10 M (NaClO4) an d at 25-degrees-C. The results were compared to analogous values of be nzoate, isophthalate and o-phthalate complexation. The apparent increa sed stability of these complexes above that expected for a typical bid entate complex is in fact merely a statistical factor. The DELTAH101 a nd DELTAS101 of these complexes reflect relatively strong dehydration of metal and ligand ions upon complex formation.