A spectroscopic study of Cm(iii) complexation with propionate in saline solutions at variable temperatures

Abstract

The complexation of Cm(III) with propionate is studied by time resolved laser fluorescence spectroscopy (TRLFS) in saline solutions (NaCl and CaCl 2 ) as a function of ionic strength, ligand concentration, and temperature. The molar fractions of the different Cm(III) species are determined by peak deconvolution of the measured fluorescence spectra. By using the specific ion interaction theory (SIT), the stability constants at zero ionic strength (log K 0 n ) of the first and second complexation steps are determined. The stability constants of the mono-and dipropionate complexes increase continuously with increasing temperature between 20-90 1C in both background electrolytes. The log K 0 n values are linearly correlated to the reciprocal temperature, indicating D r H 0 m = const. and D r C 0 p,m = 0. Therefore, the thermodynamic constants (D r H 0 m , D r S 0 m , D r G 0 m ) for the formation of the [Cm(Prop)] 2+ and [Cm(Prop) 2 ] + complexes are derived from the integrated van't Hoff equation. The results show that both reactions are entropy driven. Furthermore, neither the formation of ternary species including Ca 2+ nor a complexing effect of Cl À at elevated temperatures is observed under the chosen experimental conditions. Lastly, the ion-ion interaction coefficients of both complexed species with Cl À are derived for the first time.

Fulvic acid complexation of Eu(iii) and Cm(iii) at elevated temperatures studied by time-resolved laser fluorescence spectroscopy

“…The fact that only one Eu(III)-FA complex is formed is verified by slope analysis plotting log([Eu(III)FA] eq /[Eu(III)] eq ) vs. log([FA] eq ) (details on this procedure are given elsewhere 45 ). If only one complexed species is formed, the data points show a linear correlation.…”

Determination of complex formation constants of neptunium(V) with propionate and lactate in 0.5–2.6 m NaCl solutions at 22–60°C using a solvent extraction technique

“…Conditional log β c values were corrected to stability constant log β°(T) at infinite dilution for each temperature using SIT approach as described above. As suggested by previous work, variation of ε(i,k) with T (< ±0.05 kg•mol -1 ) can be neglected [34,35]. With the hypothesis that the molal standard reaction enthalpy Δ r H°m and entropy Δ r S°m are not changing with temperature (i.e.…”

Np(v) complexation with propionate in 0.5–4 M NaCl solutions at 20–85 °C

“…At 298.15 K and [NaClO 4 ] = 1.05 m, Rao et al 25 determined Δ r H m = 18.1 ± 1.8 kJ mol −1 and Δ r S m = 75 ± 6 J mol −1 K −1 , which are comparable to our present results for the propionate system. In general, positive Δ r H 0 m and Δ r S 0 m are found for actinide complexes with monocarboxylic ligands, for example, Cm(III)-(Prop) +2 (Δ r H 0 m = 5.7 ± 1.8 kJ mol −1 and Δ r S 0 m = 84 ± 5 J mol −1 K −1 ); 28 or U(VI)(Acetate) + (Δ r H 0 m = 14.5 ± 1.5 kJ mol −1 and Δ r S 0 m = 104 ± 6 J mol −1 K −1 ) 29 For all these actinides, the magnitude of Δ r S 0 m is comparable because both the acetate and propionate coordinate mainly in a bidentate fashion, replacing two water molecules in the first coordination shell of the actinide.…”

“…Log β(T ) is corrected to I = 0 for each temperature by applying the SIT as described in the previous section to obtain log β 0 (T ) (Table S1 †). As a first approach, heat capacity was hypothesized to be zero as observed, for instance, in a recent Cm(III)-propionate complexation study, 28 i.e. the molal standard reaction enthalpy Δ r H 0 m and entropy Δ r S 0 m do not vary with temperature between 20 and 85 °C.…”