A Uranyl Peroxide Dimer in the Gas Phase

The gas-phase uranyl peroxide dimer, [(UO2)2(O2)(L)2]2+ where L = 2,2’-trifluoroethylazanediyl)bis(N,N’-dimethylacetamide), was synthesized by electrospray ionization of a solution of UO22+ and L. Collision induced dissociation of this dimer resulted in endothermic O-atom elimination to give [(UO2)2(O)(L)2]2+, which was found to spontaneously react with water via exothermic hydrolytic chemisorption to yield [(UO2)2(OH)2(L)2]2+. Density functional theory computations of the energies for the gas-phase reactions are in accord with observations. The structures of the observed uranyl dimer were computed, with that of the peroxide of particular interest as a basis to evaluate the formation of condensed phase uranyl peroxides with bent structures. The computed dihedral angle in [(UO2)2(O2)(L)2]2+ is 145o, indicating a substantial deviation from the planar structure with a dihedral angle of 180o. Energies needed to induce bending in the most elementary gas-phase uranyl peroxide complex, [(UO2)2(O2)]2+, were computed. It was found that bending from the lowest-energy planar structure to dihedral angles up to 140o required energies of