Characterization of Uranyl Coordinated by Equatorial Oxygen: Oxo in UO₃ versus Oxyl in UO₃⁺

Uranium trioxide, UO3, has a T-shaped structure with bent uranyl, UO22+, coordinated by an equatorial oxo, O2–. The of cation UO3+ is similar but oxyl, O•–. Neutral and cationic uranium trioxide nitrates were characterized collision induced dissociation (CID), infrared multiple-photon (IRMPD) spectroscopy, density functional theory. CID uranyl nitrate, [UO2(NO3)3]– (complex A1), eliminates NO2 to produce nitrate-coordinated UO3+, [UO2(O•)(NO3)2]– (B1), which ejects NO3 yield UO3 in [UO2(O)(NO3)]– (C1). Finally, C1 associates H2O afford hydroxide [UO2(OH)2(NO3)]– (D1). IRMPD B1, C1, D1 confirms equatorially nitrate(s) along the following ligands: (B1) radical oxyl O•–; (C1) oxo O2–; (D1) two hydroxyls, OH–. As are bidentate, coordination six A1, five four D1, three C1. Ligand congestion low-coordinate suggests orbital-directed bonding. Hydrolysis epitomizes inverse trans influence inert axial oxos reactive oxo. ν3 IR frequencies indicate donor ordering: O2–[best donor] ≫ O•–> OH–> NO3–.