Spectroscopic Studies on the Thermodynamics of the Complexation of Trivalent Curium with Propionate in the Temperature Range from 20 to 90 °C

Abstract

The thermodynamics of the stepwise complexation reaction of Cm(III) with propionate was studied by time resolved laser fluorescence spectroscopy (TRLFS) and UV/Vis absorption spectroscopy as a function of the ligand concentration, the ionic strength and temperature (20–90 °C). The molar fractions of the 1:1 and 1:2 complexes were quantified by peak deconvolution of the emission spectra at each temperature, yielding the log₁₀ $K_{n}^{\prime }$ values. Using the specific ion interaction theory (SIT), the thermodynamic stability constants log₁₀ $K_{n}^{0} (T)$ were determined. The log₁₀ $K_{n}^{0} (T)$ values show a distinct increase by 0.15 (n = 1) and 1.0 (n = 2) orders of magnitude in the studied temperature range, respectively. The temperature dependency of the log₁₀ $K_{n}^{0} (T)$ values is well described by the integrated van’t Hoff equation, assuming a constant enthalpy of reaction and $\Updelta_{\text{r}} C^\circ_{{p,{\text{m}}}} = 0,$ yielding the thermodynamic standard state $\left( {\Updelta_{\text{r}} H^\circ_{\text{m}} ,\Updelta_{\text{r}} S^\circ_{\text{m}} ,\Updelta_{\text{r}} G^\circ_{\text{m}} } \right)$ values for the formation of the ${\text{Cm(Prop)}}_{n}^{3 - n}$, n = (1, 2) species.