Thermodynamic Properties of Actinide Complexes. Part VIII. Free Energy, Enthalpy, and Entropy Changes for the Formation of Uranyl(VI)- oxydiacetate, -thiodiacetate, and -iminodiacetate Complexes at 25 °C.

The stability consts. and the heats, free energies, and entropies of formation of UO22+-X(CH2CO2)2 complexes (X = O, S, NH) in aq. NaClO4 (1.0 M) at 25 °C were calcd. from potentiometric and calorimetric titration data. The results are explained in terms of the formation of simple mononuclear and protonated complexes. The stabilities of the simple complexes lie in the order NH > O > S. The difference in the stabilities of the HN(CH2CO2-)2 and O(CH2CO2-)2 complexes is mainly enthalpic but the relatively low stability of the S(CH2CO2-)2 complex is due to an entropic effect. The HN(CH2CO2-)2 complexes are protonated on the –CO2- or N.