Structures of Plutonium(IV) and Uranium(VI) with N,N-Dialkyl Amides from Crystallography, X-ray Absorption Spectra and Theoretical Calculations

Eléonor Acher (1, 2) , Yanis Hacene Cherkaski (2) , Thomas Dumas (1, 2) , Christelle Tamain (1, 2) , Dominique Guillaumont (1, 2) , Nathalie Boubals (2, 1) , Guilhem Javierre (2) , Christoph Hennig (3) , Pier Lorenzo Solari (4) , Marie-Christine Charbonnel (2)

1 LILA - Laboratory of Interactions Ligand-Actinide
2 DMRC - Département de recherche sur les procédés pour la mine et le recyclage du combustible
3 HZDR - Helmholtz-Zentrum Dresden-Rossendorf
4 SSOLEIL - Synchrotron SOLEIL

The structures of plutonium(IV) and uranium(VI) ions with a series of N,N-dialkyl amides ligands with linear and branched alkyl chains were elucidated from single crystal XRD, EXAFS and theoretical calculations. In the field of nuclear fuel reprocessing, N,N-dialkyl amides are alternative organic ligands to achieve the separation of uranium(VI) and plutonium(IV) from highly concentrated nitric acid solution. EXAFS analysis combined with XRD shows that the coordination structure of U(VI) is identical in the solution and in the solid state and is independent of the alkyl chain: two amide ligands and four bidentate nitrate ions coordinate the uranyl ion. With linear alkyl chains amides, Pu(IV) also adopt identical structures in the solid state and in solution with two amides and four bidentate nitrate ions. With branched alkyl chain amides, the coordination structure of Pu(IV) was more difficult to establish unambiguously from EXAFS. DFT calculations were consequently performed on a series of structures with different coordination modes. Structural parameters and Debye-Waller factors derived from the DFT calculations were used to compute EXAFS spectra without using fitting parameters. By using this methodology, it was possible to show that the branched alkyl chains amide form partly outer-sphere complexes with protonated ligands hydrogen bonded to nitrate ions.

Keywords: Monoamide; uranyl; plutonium; structure; DFT; EXAFS; ab initio debye-waller

Domains: Nuclear Theory [nucl-th]; Nuclear Experiment [nucl-ex]

Eléonor Acher, Yanis Hacene Cherkaski, Thomas Dumas, Christelle Tamain, Dominique Guillaumont, et al.. Structures of Plutonium(IV) and Uranium(VI) with N,N-Dialkyl Amides from Crystallography, X-ray Absorption Spectra and Theoretical Calculations. Inorganic Chemistry, 2016, 55 (11), pp.5558-5569. ⟨10.1021/acs.inorgchem.6b00592⟩. ⟨cea-02389660⟩