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

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 (20a90 degree 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 vanat Hoff equation, assuming a constant enthalpy of reaction and $ \Updelta_{\text{r}} C logical or circ_{{p,{\text{m}}} = 0, $ yielding the thermodynamic standard state $ \left( {\Updelta_{\text{r}} H logical or circ_{\text{m}} ,\Updelta_{\text{r}} S logical or circ_{\text{m}} ,\Updelta_{\text{r}} G logical or circ_{\text{m}} } \right) $ values for the formation of the $ {\text{Cm(Prop)}}_{n}3 - n} $ , n = (1, 2) species.