Thermodynamics of the hydration equilibrium derived from the luminescence spectra of the solid state for the case of the Eu-EDTA system

摘要

The luminescence properties of two compounds, [C(NH2)(3)][Eu(EDTA)(H2O)(3)] (I) and [C(NH2)(3)](2)[Yb0.97Eu0.03(EDTA)(H2O)(2)]ClO4 center dot 6H(2)O (II), were determined. The weighted sum of luminescence spectra of I and II was used to reproduce the spectra of the Eu-EDTA system in aqueous solution in the temperature range 276-363 K. By implementing this method it was possible to determine the thermodynamic functions (Delta H = 18113 +/- 506 J mole(-1) and Delta S = 62.5 +/- 4.9 J mole(-1) K-1) of the reaction [Eu(EDTA)(H2O)(3)](-) reversible arrow [Eu(EDTA)(H2O)(2)](-) + H2O, which is difficult using other methods.