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Title: Complexation and redox chemistry of neptunium, plutonium and americium with a hydroxylaminato ligand

Journal Article · · Chemical Science
DOI:https://doi.org/10.1039/D1SC03905A· OSTI ID:1820689
ORCiD logo [1]; ORCiD logo [2];  [2]; ORCiD logo [3];  [3];  [4]; ORCiD logo [5]; ORCiD logo [1]; ORCiD logo [3]; ORCiD logo [3]; ORCiD logo [1]; ORCiD logo [2]
  1. Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
  2. P. Roy and Diana T. Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, 231 S 34th St., Philadelphia, Pennsylvania 19104, USA
  3. Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
  4. Department of Chemistry and Biochemistry, Florida State University, 95 Chieftan Way, Tallahassee, Florida 32306, USA
  5. Materials and Physics Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
+ Show Author Affiliations

There is significant interest in ligands that can stabilize actinide ions in oxidation states that can be exploited to chemically differentiate 5f and 4f elements. Applications range from developing large-scale actinide separation strategies for nuclear industry processing to carrying out analytical studies that support environmental monitoring and remediation efforts. Here, we report syntheses and characterization of Np(IV), Pu(IV) and Am(III) complexes with N-tert-butyl-N-(pyridin-2-yl)hydroxylaminato, [2-(tBuNO)py]–(interchangeable hereafter with [(tBuNO)py]–), a ligand which was previously found to impart remarkable stability to cerium in the +4 oxidation state. An[(tBuNO)py]4 (An = Pu, 1; Np, 2) have been synthesized, characterized by X-ray diffraction, X-ray absorption, 1H NMR and UV-vis-NIR spectroscopies, and cyclic voltammetry, along with computational modeling and analysis. In the case of Pu, oxidation of Pu(III) to Pu(IV) was observed upon complexation with the [(tBuNO)py]– ligand. The Pu complex 1 and Np complex 2 were also isolated directly from Pu(IV) and Np(IV) precursors. Electrochemical measurements indicate that a Pu(III) species can be accessed upon one-electron reduction of 1 with a large negative reduction potential (E1/2 = –2.26 V vs. Fc+/0). Applying oxidation potentials to 1 and 2 resulted in ligand-centered electron transfer reactions, which is different from the previously reported redox chemistry of UIV[(tBuNO)py]4 that revealed a stable U(V) product. Treatment of an anhydrous Am(III) precursor with the [(tBuNO)py]– ligand did not result in oxidation to Am(IV). Instead, the dimeric complex [AmIII(μ2-(tBuNO)py)((tBuNO)py)2]2 (3) was isolated. Complex 3 is a rare example of a structurally characterized non-aqueous Am-containing molecular complex prepared using inert atmosphere techniques. Predicted redox potentials from density functional theory calculations show a trivalent accessibility trend of U(III) < Np(III) < Pu(III) and that the higher oxidation states of actinides (i.e., +5 for Np and Pu and +4 for Am) are not stabilized by [2-(tBuNO)py]–, in good agreement with experimental observations.

Research Organization:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE Laboratory Directed Research and Development (LDRD) Program
Grant/Contract Number:
89233218CNA000001; SC0016568; 20180703PRD1
OSTI ID:
1820689
Alternate ID(s):
OSTI ID: 1835805
Report Number(s):
LA-UR-21-27074; CSHCBM
Journal Information:
Chemical Science, Journal Name: Chemical Science Vol. 12 Journal Issue: 40; ISSN 2041-6520
Publisher:
Royal Society of Chemistry (RSC)Copyright Statement
Country of Publication:
United Kingdom
Language:
English

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