Characterization of Uranyl Coordinated by Equatorial Oxygen: Oxo in UO 3 versus Oxyl in UO 3

Uranium trioxide, UO3, has a T-shaped structure with bent uranyl, UO22+, coordinated by an equatorial oxo, O2-. The structure of cation UO3+ is similar but with an equatorial oxyl, O center dot-. Neutral and cationic uranium trioxide coordinated by nitrates were characterized by collision induced dissociation (CID), infrared multiple-photon dissociation (IRMPD) spectroscopy, and density functional theory. CID of uranyl nitrate, [UO2 (NO3)(3)](-) (complex A1), eliminates NO2 to produce nitrate-coordinated UO3+, [UO2 (O-center dot)(NO3)(2)](-) (BI), which ejects NO3 to yield UO3 in [UO2 (O)(NO3)](-) (C1). Finally, C1 associates with H2O to afford uranyl hydroxide in [UO2(OH)(2) (NO3)](-) (D1). IRMPD of B1, C1, and D1 confirms uranyl equatorially coordinated by nitrate(s) along with the following ligands: (B1) radical oxyl O center dot-; (C1) oxo O2-; and (D1) two hydroxyls, OH- . As the nitrates are bidentate, the equatorial coordination is six in A1, five in B1, four in D1, and three in C1. Ligand congestion in low-coordinate C1 suggests orbital-directed bonding. Hydrolysis of the equatorial oxo in C1 epitomizes the inverse trans influence in UO3, which is uranyl with inert axial oxos and a reactive equatorial oxo. The uranyl nu(3) IR frequencies indicate the following donor ordering: O2- [best donor] >> O center dot- > OH-> NO3-