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A tetrahedral neptunium(V) complex

Nature Chemistry (2024)Cite this article

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Abstract

Neptunium is an actinide element sourced from anthropogenic production, and, unlike naturally abundant uranium, its coordination chemistry is not well developed in all accessible oxidation states. High-valent neptunium generally requires stabilization from at least one metal–ligand multiple bond, and departing from this structural motif poses a considerable challenge. Here we report a tetrahedral molecular neptunium(V) complex ([Np5+(NPC)4][B(ArF5)4], 1-Np) (NPC = [NPtBu(pyrr)2]−; tBu = C(CH3)3; pyrr = pyrrolidinyl (N(C2H4)2); B(ArF5)4 = tetrakis(2,3,4,5,6-pentafluourophenyl)borate). Single-crystal X-ray diffraction, solution-state spectroscopy and density functional theory studies of 1-Np and the product of its proton-coupled electron transfer (PCET) reaction, 2-Np, demonstrate the unique bonding that stabilizes this reactive ion and establishes the thermochemical and kinetic parameters of PCET in a condensed-phase transuranic complex. The isolation of this four-coordinate, neptunium(V) complex reveals a fundamental reaction pathway in transuranic chemistry.

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Fig. 1: Synthesis of 1-Np and 2-Np.
Fig. 2: Structures and spectroscopy of compounds.
Fig. 3: Comparative α-MO energy diagrams of 1-U and 1-Np.
Fig. 4: PCET reactivity of 1-Np.

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Data availability

X-ray data are available free of charge from the Cambridge Crystallographic Data Centre under reference ID nos. 2280905 (1-Np), 2280906 (2-Np) and 2280907 (Np-Cl). Additional spectroscopic and computational data are included in the supplementary data files. The source datasets generated and/or analysed during the current study, including computational coordinates/energies and processed spectroscopic data, have been deposited in the figshare database under accession code https://doi.org/10.6084/m9.figshare.24309463 (ref. 51). Source data are provided with this paper.

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Acknowledgements

We thank C. Windorff (NMSU) for his support during laboratory set-up and the initial transuranic synthesis. This material is based on work supported by the United States Department of Energy, Office of Science, Office of Basic Energy Sciences, Heavy Element Chemistry programme under award no. DE-SC0019385 (J.E.N., K.S.O. and H.S.L.P.) at the Georgia Institute of Technology. Computational work was conducted using the computational resources at the Ohio Supercomputer Center and the ARCC HPC cluster at the University of Akron (C.M.S. and I.A.P.), as well as at the University of South Dakota, supported by the United States Department of Energy, Office of Science, Office of Basic Energy Sciences, Heavy Element Chemistry programme under award no. DE-SC0023022 (S.R.C. and B.V.) and by the high-performance computing systems at the University of South Dakota, funded by the National Science Foundation under award no. OAC-1626516 (S.R.C. and B.V.).

Author information

Author notes

  1. These authors contributed equally: Julie E. Niklas, Kaitlyn S. Otte.

Authors and Affiliations

  1. School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA, USA

    Julie E. Niklas, Kaitlyn S. Otte, John Bacsa & Henry S. La Pierre

  2. Department of Chemistry, The University of Akron, Akron, OH, USA

    Chad M. Studvick & Ivan A. Popov

  3. Department of Chemistry, University of South Dakota, Vermillion, SD, USA

    Sabyasachi Roy Chowdhury & Bess Vlaisavljevich

  4. Institut für Anorganische Chemie, RWTH Aachen University, Aachen, Germany

    Florian Kleemiss

  5. Nuclear and Radiological Engineering and Medical Physics Program, School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA

    Henry S. La Pierre

  6. Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA, USA

    Henry S. La Pierre

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Contributions

J.E.N., K.S.O. and H.S.L.P. conceived the idea presented in this publication. H.S.L.P., I.A.P. and B.V. supervised the project and acquired funding. J.E.N., K.S.O. and H.S.L.P. developed the syntheses and performed the spectroscopic characterization. Crystallographic characterization was performed by K.S.O., J.E.N., H.S.L.P., J.B. and F.K. Theoretical calculations and analysis were performed by C.M.S., S.R.C., B.V. and I.A.P. Analysis and visualization were performed by J.E.N., K.S.O., C.M.S., S.R.C., I.A.P., B.V. and H.S.L.P. The first draft was written by J.E.N., K.S.O., C.M.S. and S.R.C., with contributions from all authors. The paper was reviewed and edited by H.S.L.P., I.A.P. and B.V., with input from all authors.

Corresponding authors

Correspondence to Ivan A. Popov or Henry S. La Pierre.

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Nature Chemistry thanks Valerie Vallet and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Table 1 Selected bond metrics for An5+ and An4+ species (An = Np, U)
Full size table

Extended Data Fig. 1 PCET reactivity on the NMR timescale.

31P{1H} NMR spectra of 1-Np in THF-d8, prepared at t0 showing loss of 1-Np and ingrowth of 2-Np signals. Integration values are normalized to a sum of 1.0 and represent averages over independently processed and integrated data.

Extended Data Fig. 2 BDFE calculations.

Thermodynamic equations employed for calculating the N–H bond dissociation free energy of 2-Np through H atom transfer mediated by TEMPO-H.

Supplementary information

Supplementary Information

Supplementary Information (Experimental Details, Spectroscopic Data, Computational Details, References), Figs. 1–29 and Tables 1–13.

Supplementary Data 1

Crystallographic data for compound 1-Np; CCDC reference no. 2280905.

Supplementary Data 2

Crystallographic data for compound 2-Np; CCDC reference no. 2280906.

Supplementary Data 3

Crystallographic data for compound Np-Cl; CCDC reference no. 2280907.

Supplementary Data 4

DFT atomic coordinates.

Source data

Source Data Fig. 2

UV-vis-NIR source data for 1-Np at 8 mM and 0.1 mM.

Source Data Fig. 3

DFT single point energy calculations using an implicit solvent model of THF.

Source Data Fig. 4

31P NMR integration values at each time point and SD calculation.

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Niklas, J.E., Otte, K.S., Studvick, C.M. et al. A tetrahedral neptunium(V) complex. Nat. Chem. (2024). https://doi.org/10.1038/s41557-024-01529-6

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