Improving the theoretical description of Ln(iii)/An(iii) separation with phosphinic acid ligands: a benchmarking study of structure and selectivity

Robert C. Chapleski, Alexander S. Ivanov, Kirk A. Peterson, Vyacheslav S. Bryantsev

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

The efficient separation of trivalent lanthanides from minor actinides with soft-donor ligands, while showing experimental promise, has theorists continuing to search for suitable approaches for describing and interpreting selectivity. To remedy this, we employ several computational methods in describing the structure of model M(H2PX2)3complexes, with M = Eu and Am, and X = O, S, Se, and Te, and predicting the selectivity of model phosphinic acid ligands in Eu(iii)/Am(iii) separation. After first establishing a set of MP2 and CCSD(T)-DKH3 results as benchmarks, we evaluate several density functionals and descriptions of valence shells for their accuracy with respect to metal-ligand bonding and selectivity. We find that commonly employed functionals with a 0-27% range of exact exchange used with small-core effective core potentials or with an explicit treatment of the relativistic effects (DKH2) incorrectly predict a decrease in the metal-ligand bond distance in going from Eu(iii) to Am(iii) and completely fail to track a selectivity trend, even giving a wrong sign for some or all ligands. Surprisingly, when these functionals are used in conjunction with an f-in-core description of metal ions, the correct trend in selectivity is recovered, though Am-X distances are overestimated in relation to Eu-X. Functionals with high components of exact exchange (50%) and double-hybrid functionals are reasonably aligned with benchmark results, pointing to the problems of DFT with small exact exchange fractions to handle f-electrons. Natural bond orbital analyses reveal that these poorly performing functionals disproportionately overpopulate outer f orbitals in the model complexes. We anticipate that recommendations resulting from this work will lead to more accurate theoretical descriptions of lanthanide/actinide selectivity with soft-donor chalcogen-based ligands in the future.

Original languageEnglish
Pages (from-to)19558-19570
Number of pages13
JournalPhysical Chemistry Chemical Physics
Volume23
Issue number35
DOIs
StatePublished - Sep 21 2021

Funding

† This manuscript has been authored in part by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan). ‡ Electronic supplementary information (ESI) available: Additional MP2 reaction energies, second-order stabilization energies, additional basis functions for core-valence basis sets, recontracted basis sets for Eu(III) and Am(III) and spatial coordinates for all structures. See DOI: 10.1039/d1cp02466c This work was supported by the Nuclear Technology Research and Development Program, Office of Nuclear Energy, US Department of Energy. This research used resources of the National Energy Research Scientific Computing Center (NERSC) and the Computer and Data Environment for Science (CADES) at Oak Ridge National Laboratory, both of which are supported by the Office of Science, U.S. Department of Energy, under Contracts DEAC02-05CH11231 and DE-AC05-00OR22725, respectively. KAP was supported by the Heavy Element Chemistry Program, Office of Basic Energy Sciences, U.S. Department of Energy, Grant No. DE-SC0008501.

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