Uranium Oxo and Superoxo Cations Revealed Using Infrared Spectroscopy in the Gas Phase

Abstract

The UO4 + and UO6 + cations are produced in a supersonic molecular beam by laser vaporization and studied with infrared laser photodissociation spectroscopy using rare gas atom predissociation. The argon complexes UO4 +Ar2 and UO6 +Ar2 are mass-selected in a reflectron time-of-flight spectrometer and excited with an IR-OPO laser system in the range of the O–U–O and O–O stretching vibrations. These same systems are studied with computational quantum chemistry. UO4 + is found to have a central UO2 core, with an additional η2 coordinated oxygen molecule. Charge transfer/oxidation gives the system the character of a UO2 2+, O2 – ion pair. UO6 + has this same core structure, with an additional weakly bound oxygen molecule in an η1 coordination configuration. The O–U–O stretch is sensitive to the local environment and approximates the vibration of the isolated uranyl cation in these systems.

Gas-Phase Reactions of Molecular Oxygen with Uranyl(V) Anionic Complexes—Synthesis and Characterization of New Superoxides of Uranyl(VI)

“…10 Recently, we observed gas-phase O 2 -substitution in an anionic uranyl(V) complex, [UO 2 (CH 3 SO 2 )(SO 2 )] − , in which the SO 2 − ligand is replaced by O 2 to produce a peroxide complex concomitant with oxidation to uranyl(VI). 11 Formation of [UO 2 (CH 3 SO 2 ) 2 (O 2 )] − by O 2 addition to the precursor complex [UO 2 (CH 3 SO 2 ) 2 ] − was also observed, indicating that uranyl(V) coordinated by anionic CH 3 SO 2 − ligands can add O 2 to form a superoxo complex.…”

“…10 Recently, we observed gas-phase O 2 -substitution in an anionic uranyl(V) complex, [UO 2 (CH 3 SO 2 )(SO 2 )] − , in which the SO 2 − ligand is replaced by O 2 to produce a peroxide complex concomitant with oxidation to uranyl(VI). 11 Formation of [UO 2 (CH 3 SO 2 ) 2 (O 2 )] − by O 2 addition to the precursor complex [UO 2 (CH 3 SO 2 ) 2 ] − was also observed, indicating that uranyl(V) coordinated by anionic CH 3 SO 2 In the present work we report a systematic study of O 2 -addition reactions to anionic uranyl(V) complexes [UO 2 X 2 ] − with various X − ligands, from monatomic halides to polyatomic ligands with different coordinating atoms, which present varied intrinsic properties such as the number of vibrational degrees of freedom and gas-phase basicities.…”

Revealing Disparate Chemistries of Protactinium and Uranium. Synthesis of the Molecular Uranium Tetroxide Anion, UO4–

“…17,27,32 A goal of gas-phase chemistry is to identify spontaneous exothermic reactions that can alternatively result in seemingly exotic high-energy species such as UO 4 − under thermal conditions. One approach to achieve such reactions is by selecting precursors that have ligands that decompose absent substantial kinetic barriers to yield stable neutral molecules, such as CO 2 .…”

Synthesis and hydrolysis of gas-phase lanthanide and actinide oxide nitrate complexes: a correspondence to trivalent metal ion redox potentials and ionization energies

“…) are stable ligands, such as in [U VI O 2 (O 2 )] + . 28 ). 29 It is apparent that the assumption that all oxygen atoms in metal oxide clusters can be considered as O 2À is not well founded.…”