The thermodynamics of the formation of complexes between diethylene-triaminepenta-acetic acid and some tervalent metal ions

Abstract

The changes in enthalpy accompanying the formation of complexes between diethylenetriaminepenta-acetic acid and some tervalent metal ions, in aqueous solution at an ionic strength of 0·1M, have been measured by use of an isothermal fusion calorimeter. The results for the complexes of Al³⁺, Sc³⁺, Y³⁺, and La³⁺ are 7·4, – 7·6, – 6·5, and – 5·2 kcal. mole^–1 respectively. The enthalpies of complex formation have been combined with the appropriate free-energy changes to give the entropy changes. The factors which influence the stability of these complexes have been discussed.