The complexation and thermodynamics of neptunium(v) with acetate in aqueous solution

Abstract

The complexation of NpO2+with acetate is studied in aqueous solution by absorption spectroscopy as a function of the total ligand concentration (NaAc), ionic strength (Im= 0.5–4.0 mol kg−1Na+(Cl−/ClO4−)) and temperature (T= 20–85 °C).

Complexation of Np(V) with the Dicarboxylates, Malonate, and Succinate: Complex Stoichiometry, Thermodynamic Data, and Structural Information

“…In all systems, no significant temperature dependence of Δε n ° (Θ) is observed and averaged, temperature-independent Δε n ° values are calculated (given as solid lines). This is in good agreement with the negligible temperature dependence of Δε n ° (Θ) values for Np­(V) and An­(III) complexes with various organic and inorganic ligands described in the literature . ,,,,,, The binary ion–ion interaction coefficients ε j , k of the NpO 2 (L) n 1–2 n complexes (L 2– = Mal 2– , Succ 2– ) with Na + are calculated according to the SIT using eq and the interaction coefficients ε­(NpO 2 + , ClO 4 – ) = 0.25 ± 0.05 and ε­(NpO 2 + , Cl – ) = 0.09 ± 0.05 given in the NEA-TDB. The values of ε­(Na + , Mal 2– ) = −0.05 ± 0.03 and ε­(Na + , Succ 2– ) = 0.09 ± 0.02 are calculated from literature data using the SIT procedure. ,, …”

“…This is not the case for NpO 2 (Mal) n 1–2 n and NpO 2 (Succ) n 1–2 n ( n = 1, 2) as slight deviations are observed for the values determined in NaCl or NaClO 4 media. In previous studies, it was shown that these discrepancies originate from a defective ε­(NpO 2 + , ClO 4 – ) = 0.25 ± 0.05 reported in the NEA-TDB. ,,, Nevertheless, the log β n ° (Θ) of the respective complex species obtained in NaCl or NaClO 4 are in excellent agreement. Thus, the ionic strength dependence of log β n ° (Θ) is accurately described with the Δε n ° determined in this work.…”

“…The temperature-induced shift of the Np­(V) absorption to shorter wavelengths was already observed in previous studies. ,− In the literature, this effect was explained by changes of the physical properties (e.g., dielectric constant, refractive index, polarity) of water with increasing temperature affecting the electronic absorption of the NpO 2 + ions. , Also changes of the hydration in the first and second solvation sphere or changes of the complex geometries due to increasing temperatures might contribute to this shift. , …”

“…54,56−58 In the literature, this effect was explained by changes of the physical properties (e.g., dielectric constant, refractive index, polarity) of water with increasing temperature affecting the electronic absorption of the NpO 2 + ions. 54,56 Also changes of the hydration in the first and second solvation sphere or changes of the complex geometries due to increasing temperatures might contribute to this shift. 57,58 The temperature-induced shift of the absorption band of the Np(V) ion to shorter wavelengths is contrary to the bathochromic shift of the spectra, which results from the complexation of Np(V) with malonate and succinate.…”

“…This is in good agreement with the negligible temperature dependence of Δε n °(Θ) values for Np(V) and An(III) complexes with various organic and inorganic ligands described in the literature . 23,32,53,54,56,71,72 The binary ion− ion interaction coefficients ε j,k of the NpO 2 (L) n 1−2n complexes (L 2− = Mal 2− , Succ 2− ) with Na + are calculated according to the SIT using eq 6 and the interaction coefficients ε(NpO and ε(Na + , Succ 2− ) = 0.09 ± 0.02 are calculated from literature data using the SIT procedure. 63,64,73 products educts…”