Modelling the Effect of Temperature on the Stability of Bromide and Carbonate Complexes of Europium, Gadolinium, Terbium and Determination of their Thermodynamic Functions

摘要

A method has been developed for calculating the stability constants of inorganic complexes of rare-earth metals at various temperatures, based on analysis of the literature data by obtaining a linear regression equation on the form: lg_L K(T_1) = A(T_1) + 5(T_1) lg_L K(T_2). Using this method, the stability constants of bromide LnBr~(2+) and carbonate LnCO_3~+ complexes of europium, terbium, and gadolinium in aqueous solutions at temperatures of 50, 75, and 100 °C were obtained. The obtained values of the coefficients A(T_1) and B(T_1) of the linear regression equation can be used to calculate the stability constants of complexes of europium, terbium, and gadolinium with other inorganic ligands at given temperatures. Based on the temperature dependence of the stability constants of bromide and carbonate complexes, their standard entropies and enthalpies of formation were calculated. Based on the obtained values of the thermodynamic functions, an assumption was made about the outer-sphere or inner-sphere nature of the complex.