Speciation, thermodynamics and structure of Np(v) oxalate complexes in aqueous solution

• Verfasst von: Maiwald, Martin M. [VerfasserIn]
• Verfasst von: Trumm, Michael [VerfasserIn]
• Verfasst von: Dardenne, K. [VerfasserIn]
• Verfasst von: Rothe, J. [VerfasserIn]
• Verfasst von: Skerencak-Frech, A. [VerfasserIn]
• Verfasst von: Panak, Petra [VerfasserIn]
• Titel: Speciation, thermodynamics and structure of Np(v) oxalate complexes in aqueous solution
• Verf.angabe: M.M. Maiwald, M. Trumm, K. Dardenne, J. Rothe, A. Skerencak-Frech and P.J. Panak
• E-Jahr: 2020
• Jahr: Oct 14 2020
• Umfang: 13 S.
• Fussnoten: Gesehen am 09.11.2020
• Titel Quelle: Enthalten in: Dalton transactions
• Ort Quelle: London : Soc., 1972
• Jahr Quelle: 2020
• Band/Heft Quelle: 49(2020), 38, Seite 13359-13371
• ISSN Quelle: 1477-9234
• DOI: doi:10.1039/d0dt02379e
• Datenträger: Online-Ressource
• Sprache: eng
• Sach-SW: acetate
• Sach-SW: actinide research
• Sach-SW: alkali-metal complexes
• Sach-SW: biological interest
• Sach-SW: cm(iii)
• Sach-SW: disposal
• Sach-SW: dissolved organic-matter
• Sach-SW: ine-beamline
• Sach-SW: neptunium(v) complexation
• Sach-SW: temperature
• K10plus-PPN: 1738225690

Abstract

The speciation, thermodynamics and structure of the Np(v) (as the NpO2+ cation) complexes with oxalate (Ox(2-)) are studied by different spectroscopic techniques. Near infrared absorption spectroscopy (Vis/NIR) is used to investigate complexation reactions as a function of the total ligand concentration ([Ox(2-)](total)), ionic strength (l(m) = 0.5-4.0 mol kg(-1) Na+ (Cl-/ClO4-)) and temperature (T = 20-85 degrees C) for determination of the complex stoichiometry and thermodynamic functions (log beta(0)(n)(T), Delta H-r(n)0, Delta S-r(n)0). Besides the solvated NpO2+ ion, two NpO2+ oxalate species (NpO2(Ox)(n)(1-2n); n = 1, 2) are identified. With increasing temperature a decrease of the molar fractions of the 1 : 1 - and 1: 2 - complexes is observed. Application of the law of mass action yields the temperature dependent conditional stability constants log beta(n)' (T) at a given ionic strength which are extrapolated to IUPAC reference state conditions (l(m) = 0) according to the specific ion interaction theory (SIT). The log beta(0)(n) (T) values of both complex species (log beta(0)(1)(25 degrees C) = 4.53 +/- 0.12; log beta(0)(2)(25 degrees C) = 6.22 +/- 0.24) decrease with increasing temperature confirming an exothermic complexation reaction. The temperature dependence of the thermodynamic stability constants is described by the integrated van't Hoff equation yielding the standard reaction enthalpies (Delta H-r(1)0 = -13 +/- 0.7 kJ mol(-1); Delta H-r(2)0 = -8.7 t 1.4 kJ mol(-1)) and entropies (Delta S-r(1)0 = 82 +/- 2 J mol(-1) K-1; Delta S-r(2)0 = 90 +/- 5 J mol(-1) K-1) for the complexation reactions. In addition, the sum of the specific binary ion-ion interaction coefficients Delta epsilon(0)(n)(T) for the complexation reactions are obtained from SIT modelling as a function of the temperature. The structure of the complexes and the coordination mode of oxalate are investigated using EXAFS spectroscopy and quantum chemical calculations. The results show, that in case of both species NpO2(Ox)(-) and NpO2(Ox)(2)(3-), chelate complexes with 5-membered rings are formed.