Characterization of Bonding Motifs in Actinide Fluoride Compounds with the Actinide (Ac-U) in the Maximum Oxidation...

Density functional theory (B3LYP) and correlated molecular orbital theory (CCSD(T)) calculations were used to predict the properties of novel actinide-fluoride complexes formed by the addition of a fluorine to AnF_n compounds, with actinides in their normal maximum oxidation state (n), leading to the formation of an ion-pair complex [AnF_n-1⁺][F₂^-] for the earlier actinides (Ac, Th, and Pa). UF₇ prefers a structure with a weakly associated fluorine, forming a [UF₆][F^•] complex, likely due to steric hindrance. Ionization of [AnF_n-1⁺][F₂^-] forms a weakly bound [AnF_n-1⁺][F₂] complex. Ionization of AnF_n leads to the formation of [AnF_n-2²⁺][F₂^-] complex so that the electron is not removed from the actinide and maintains the An oxidation state. The ionization energies, An-F bond dissociation energies, and enthalpy for the loss of F₂^0/- of these complexes are in agreement with the available experimental data. The fluoride affinities of AnF_n and the electron affinities of AnF_n+1 were calculated. The fluoride affinities are large and comparable to those of AsF₅ and SbF₅ so they are strong Lewis acids. The electron affinities are sizable, indicating that AnF_n+1^- will be powerful oxidizing agents and should be considered in models of molten salt reactors when fluoride is present.