Investigation of Uranyl Perchlorate Anion Complexes in the Gas Phase via Infrared Multiphoton Dissociation and Collision‐Induced Dissociation

The infrared multiphoton dissociation spectrum of the gas-phase uranyl perchlorate anion ([UO₂(ClO₄)₃]^-) was measured. The asymmetric uranyl stretch lies somewhere between 930 and 1030 cm^-1, though it could not be deconvoluted from a closely located perchlorate stretching mode. The experimentally measured spectrum was in good agreement with spectra calculated using density functional theory with the B3LYP and TPSSh functionals and Grimme's D3 dispersion corrections with Becke-Johnson damping. The calculations suggest that the asymmetric uranyl stretch lies in the range of 970-980 cm^-1, about 20-30 cm^-1 higher than for the analogous uranyl trinitrato complex and consistent with perchlorate as a weaker ligand than nitrate. Like the uranyl trinitrato anion, fragmentation of [UO₂(ClO₄)₃]^- by collision-induced dissociation resulted in loss of a ClO₃ ^• radical to form [UO₃(ClO₄)₂]^-. Infrared multiphoton dissociation measurements of [UO₃(ClO₄)₂]^- indicate that the structure of the product ion has an O^- ligand bound to the uranyl in a T-arrangement and two perchlorate ligands, matching the findings from uranyl nitrato complexes. The uranyl stretch in this complex was slightly separated from the perchlorate modes and was measured at 906 cm^-1, slightly higher than for the analogous nitrate complex, again consistent with perchlorate as a weaker ligand than nitrate in the gas phase.