Gas-phase uranyl peroxide dimers [(UVIO2)2(O2)(L)2]2+ are produced in remarkably high abundance by electrospray ionization (ESI) of uranyl and tetradentate hard-soft (2O-2N) donor ligands L. The three such ligands employed in this work are a 2,9-diamide-1,10-phenanthroline (DAPhen) and two bis-lactam-1,10-phenanthrolines (BLPhen). The dimer assignments were confirmed by mass spectrometric mass shifts using isotopically substituted U18O22+, by collision induced dissociation (CID), and by infrared multiple photon dissociation (IRMPD) spectroscopy. CID of [(UVIO2)2(O2)(L)2]2+ results in peroxide bond cleavage to give [UVO2L]+, which chemisorbs O2 to yield [UVIO2(O2)L]+, and in O atom elimination to give [(UVIO2)2(O)(L)2]2+, which chemisorbs H2O to yield [(UVIO2)2(OH)2(L)2]2+. Agreement of the measured and density functional theory (DFT) computed IR spectra confirm the assignments as [(UVIO2)2(O2)(L)2]2+ peroxides. IRMPD spectra for [(UVIO2)2(O2)(L)(L′)]2+, where L and L′ are the same or different DAPhen/BLPhen ligands, reveal a nearly constant uranyl asymmetric stretch frequency, ν3, as is also predicted by DFT. The near invariance of ν3 suggests similar uranyl-ligand bonding interactions, which appears as inconsistent with the disparate solution affinities of the three ligands for metal ions. The underlying basis for the near-constant ν3, including differences between gas and solution complexation, is being further assessed.

Synthesis and characterization of gas-phase uranyl peroxide dimer complexes

256th National Meeting (2018)

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