Extraction of Uranium(VI) and Plutonium(IV) by New Tri Alkylcarbamides

Molecular and Supramolecular Study of Uranium/Plutonium Liquid-Liquid Extraction with N,N-Dialkylamides

In the context of the separation of uranium and plutonium from spent fuel allowed by N,N-dialkylamides, three regioisomers of N,N-di(2-ethylhexyl) butyramide (DEHBA or ββ) and the diastereopure isomers of N-(2-ethylhexyl)-N-(oct-3-yl)butyramide (EHOBA or αβ) were synthesized to assess their extraction performance and to study the mechanisms at the origin of the differences observed between the stereo- and regioisomers. The N,N-dialkylamides showed differences in extraction, with a greater effect of regio- than stereoisomerism. A mechanistic study at both the molecular and supramolecular scales was initially applied to explain these effects. X-ray absorption and UV-vis spectroscopy showed that uranium is extracted by a UO2(NO3)2L2 complex, which is not very sensitive to steric hindrance, while plutonium is extracted by two complexes, Pu(NO3)4L2 and Pu(NO3)6(HL)2, which are differently affected by stereo- and regioisomerism. Investigations at the supramolecular scale also showed that Pu(NO3)4L2 complexes are disadvantaged by the bulkiness of the extractants, while Pu(NO3)6(HL)2 is favored by the preformation of larger supramolecular aggregates.

PuCl3{CoCp[OP(OEt)2]3}: transuranic elements entering the field of heterometallic molecular chemistry

Recent advances enabled the discovery of heterometallic molecules for many metals: main group, d-block, lanthanides, and some actinides (U, Th). These complexes have at least two different metals joined by bridging ligands or by direct metal-metal bonding interactions. They are attractive because they can enable chemical cooperativity between metals from different parts of the periodic table. Some heterometallics provide access to unique reactivity and others exhibit physical properties that cannot be accessed by homometallic species. We envisioned that transuranic heterometallics might similarly enable new transuranic chemistry, though synthetic routes to such compounds have yet to be developed. Reported here is the first synthesis of a molecular transuranic complex that contains plutonium (Pu) and cobalt (Co). Our analyses of PuCl3{CoCp[OP(OEt)2]3} showed Pu(iv) and Co(iii) were present and suggested that the Pu(iv) oxidation state was stabilized by the electron donating phosphite ligands. This synthetic method - and the demonstration that Pu(iv) can be stabilized in a heterobimetallic molecular setting - provides a foundation for further exploration of transuranic multimetallic chemistry.

Assessing MP2 frozen natural orbitals in relativistic correlated electronic structure calculations

The high computational scaling with the basis set size and the number of correlated electrons is a bottleneck limiting applications of coupled cluster algorithms, in particular for calculations based on two- or four-component relativistic Hamiltonians, which often employ uncontracted basis sets. This problem may be alleviated by replacing canonical Hartree-Fock virtual orbitals by natural orbitals (NOs). In this paper, we describe the implementation of a module for generating NOs for correlated wavefunctions and, in particular, second order Møller-Plesset perturbation frozen natural orbitals (MP2FNOs) as a component of our novel implementation of relativistic coupled cluster theory for massively parallel architectures [Pototschnig et al. J. Chem. Theory Comput. 17, 5509, (2021)]. Our implementation can manipulate complex or quaternion density matrices, thus allowing for the generation of both Kramers-restricted and Kramers-unrestricted MP2FNOs. Furthermore, NOs are re-expressed in the parent atomic orbital (AO) basis, allowing for generating coupled cluster singles and doubles NOs in the AO basis for further analysis. By investigating the truncation errors of MP2FNOs for both the correlation energy and molecular properties-electric field gradients at the nuclei, electric dipole and quadrupole moments for hydrogen halides HX (X = F-Ts), and parity-violating energy differences for H₂Z₂ (Z = O-Se)-we find MP2FNOs accelerate the convergence of the correlation energy in a roughly uniform manner across the Periodic Table. It is possible to obtain reliable estimates for both energies and the molecular properties considered with virtual molecular orbital spaces truncated to about half the size of the full spaces.

Stereochemically enriched extractants for the extraction of actinides

Stereoisomers of monoamide highlight the importance of the extractant chirality for U/Pu extraction.