Uranyl(VI) complexes of ethylene-1,2-dioxydiacetic acid and ethylene-1,2-diaminodiacetic acid in aqueous solution: a potentiometric and calorimetric study

Abstract

The stability constants and the changes in enthalpy and entropy for the formation of uranyl(VI) complexes with dicarboxylate ligands of the type (-CH 2RCH 2COO) 2 2−, where RO or NH, have been determined by potentiometric and calorimetric titrations at 25.0 °C in 1.0 mol dm −3 aqueous solution of sodium perchlorate. The ethylene-l,2-dioxydiacetate ligand forms either 1:1 and 1:2 chelated complexes or unchelated protonated complexes, owing to the low stability of the chelate ring. Because of precipitation of solid compounds only one complex of 1:1 stoichiometry was observed in the uranyl(VI)—ethylene-l,2-diaminodiacetate system. Factors influencing the stability constants and the enthalpy and entropy changes in the uranyl(VI) complexes with these potentially tetradentate ligands are discussed in comparison with analogous complexes involving bi- and tridentate dicarboxylate ligands.