Jian T, Vasiliu M, Lee ZR, Zhang Z, Dixon DA, Gibson JK. Dinuclear Complexes of Uranyl, Neptunyl, and Plutonyl: Structures and Oxidation States Revealed by Experiment and Theory.
J Phys Chem A 2022;
126:7695-7708. [PMID:
36251495 DOI:
10.1021/acs.jpca.2c06121]
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Abstract
Dinuclear perchlorate complexes of uranium, neptunium, and plutonium were characterized by reactivity and DFT, with results revealing structures containing pentavalent, hexavalent, and heptavalent actinyls, and actinyl-actinyl interactions (AAIs). Electrospray ionization produced native complexes [(AnO2)2(ClO4)3]- for An:An = U:U, Np:Np, Pu:Pu, and Np:Pu, which are intuitively formulated as actinyl(V) perchlorates. However, DFT identified lower-energy structures [(AnO2)(AnO3)(ClO4)2(ClO3)]- comprising a perchlorate fragmented to ClO3, actinyl(VI) cation AnVIO22+, and neutral AnO3. For U:U and Np:Np, and Np in Np:Pu, the coordinated AnO3 is calculated as actinyl(VI) with an equatorial oxo, [Oyl═AnVI═Oyl][═Oeq], whereas for Pu:Pu, it is plutonyl(V) oxyl, [Oyl═PuV═Oyl][-Oeq•]. The implied lower stability of PuVI versus NpVI indicates weaker Pu═Oeq versus Np═Oeq bonding. Adsorption of O2 by the U:U complex suggests oxidation of UV to UVI, corroborating the assignment of perchlorate [(AnVO2)2(ClO4)3]-. DFT predicts the O2 adducts are [(AnVIO2)(O2)(AnVIO2)(ClO4)3]- with actinyls oxidized from +V to +VI by bridging peroxide, O22-. In accordance with reactivity, O2- addition is computed as substantially exothermic for U:U and least favorable for Pu:Pu. Collision-induced dissociation of native complexes eliminated ClO2 to yield [(AnO2)(O)2(AnO2)(ClO4)2]-, in which fragmented O atoms bridge as oxyl O-• and oxo O2- to yield uranyl(VI) and plutonyl(VI), or as oxos O2- to yield neptunyl(VII), [Oyl═NpVII═Oyl]3+.
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