Destruction and reconstruction of UO22+ using gas-phase reactions

Abstract

While the strong axial UO bonds confer high stability and inertness to UO₂²⁺, it has been shown that the axial oxo ligands can be eliminated or replaced in the gas-phase using collision-induced dissociation (CID) reactions. We report here tandem mass spectrometry experiments initiated with a gas-phase complex that includes UO₂²⁺ coordinated by a 2,6-difluorobenzoate ligand. After decarboxylation to form a difluorophenide coordinated uranyl ion, [UO₂(C₆F₂H₃)]⁺, CID causes elimination of CO, and then CO and C₂H₂ in sequential dissociation steps, to leave a reactive uranium fluoride ion, [UF₂(C₂H)]⁺. Reaction of [UF₂(C₂H)]⁺ with CH₃OH creates [UF₂(OCH₃)]⁺, [UF(OCH₃)₂]⁺ and [UF(OCH₃)₂(CH₃OH)]⁺. Cleavage of C–O bonds within these species results in the elimination of methyl cation (CH₃⁺). Subsequent CID steps convert [UF(OCH₃)₂]⁺ to [UO₂(F)]⁺ and similarly, [U(OCH₃)₃]⁺ to [UO₂(OCH₃)]⁺. Our experiments show removal of both uranyl oxo ligands in “top-down” CID reactions and replacement in “bottom-up” ion–molecule and dissociation steps.