title: Gas-phase reactions of molecular oxygen with uranyl(V) anionic complexes-synthesis and characterization of new superoxides of uranyl(VI).
abstract: Gas-phase complexes of uranyl(V) ligated to anions X(-) (X = F, Cl, Br, I, OH, NO3, ClO4, HCO2, CH3CO2, CF3CO2, CH3COS, NCS, N3), [UO2X2](-), were produced by electrospray ionization and reacted with O2 in a quadrupole ion trap mass spectrometer to form uranyl(VI) anionic complexes, [UO2X2(O2)](-), comprising a superoxo ligand. The comparative rates for the oxidation reactions were measured, ranging from relatively fast [UO2(OH)2](-) to slow [UO2I2](-). The reaction rates of [UO2X2](-) ions containing polyatomic ligands were significantly faster than those containing the monatomic halogens, which can be attributed to the greater number of vibrational degrees of freedom in the polyatomic ligands to dissipate the energy of the initial O2-association complexes. The effect of the basicity of the X(-) ligands was also apparent in the relative rates for O2 addition, with a general correlation between increasing ligand basicity and O2-addition efficiency for polyatomic ligands. Collision-induced dissociation of the superoxo complexes showed in all cases loss of O2 to form the [UO2X2](-) anions, indicating weaker binding of the O2(-) ligand compared to the X(-) ligands. Density functional theory computations of the structures and energetics of selected species are in accord with the experimental observations.
authors: †Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, 2695-066 Bobadela LRS, Portugal.
authors: Ana F
authors: AF
authors: Lucena
authors: †Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, 2695-066 Bobadela LRS, Portugal.
authors: José M
authors: JM
authors: Carretas
authors: †Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, 2695-066 Bobadela LRS, Portugal.
authors: Joaquim
authors: J
authors: Marçalo
authors: ‡Dipartimento di Chimica, Università della Calabria, 87030 Arcavacata di Rende, Italy.
authors: Maria C
authors: MC
authors: Michelini
authors: §Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
authors: Yu
authors: Y
authors: Gong
authors: §Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
authors: John K
authors: JK
authors: Gibson
mesh_terms: D000838:Anions / Q000737:chemistry; D005740:Gases / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry*; D011789:Quantum Theory; D013481:Superoxides / Q000737:chemistry*; D017974:Uranium Compounds / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D000838:Anions; D005740:Gases; D017974:Uranium Compounds; D013481:Superoxides; D010100:Oxygen