ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 37, Number 4
JKCSEZ 37(4)
August 20, 1993 

The thermodynamic parameters (△G, △H and △S) of lanthanides(Ⅲ)-benzoylformate complexes in aqueous solution have been determined in the ionic medium of 0.1M NaClO4 at 25℃, using pH and enthalpy titration method. The stability constants of the lanthanide(Ⅲ)-benzoylformate complexes (1 : 1) agree well with the general relationships for the bidentate ligands (e.g., logβ1 vs. pKa). Thermodynamic evidences show that the oxygen atom in ketone group is coordinated along with the carboxylate group. It is ascribed to the increasing charge density on the oxygen atom in ketone group due to the conjugation effect in the benzoylformate ligand. Thermodynamic results also indicate that the complexes are stabilized by the enthalpy effect caused by the ionic interaction of metal-oxygen bond as well as the entropy effect.