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  1. The following gas-phase uranyl/12-crown-4 (12C4) complexes were synthesized by electrospray ionization: [UO 2(12C4) 2] 2+and [UO 2(12C4) 2(OH)] +. Collision-induced dissociation (CID) of the dication resulted in [UO 2(12C4-H)] +(12C4-H is a 12C4 that has lost one H), which spontaneously adds water to yield [UO 2(12C4-H)(H 2O)] +. The latter has the same composition as complex [UO 2(12C4)(OH)] + produced by CID of [UO 2(12C4) 2(OH)] + but exhibits different reactivity with water. The postulated structures as isomeric [UO 2(12C4-H)(H 2O)] + and [UO 2(12C4)(OH)] + were confirmed by comparison of infrared multiphoton dissociation (IRMPD) spectra with computed spectra. Themore » structure of [UO 2(12C4-H)] + corresponds to cleavage of a C-O bond in the 12C4 ring, with formation of a discrete U-O eq bond and equatorial coordination by three intact ether moieties. Comparison of IRMPD and computed IR spectra furthermore enabled assignment of the structures of the other complexes. Theoretical studies of the chemical bonding features of the complexes provide an understanding of their stabilities and reactivities. Finally, the results reveal bonding and structures of the uranyl/12C4 complexes and demonstrate the synthesis and identification of two different isomers of gas-phase uranyl coordination complexes.« less
  2. Recent efforts to activate the strong uranium-oxygen bonds in the dioxo uranyl cation have been limited to single oxo-group activation through either uranyl reduction and functionalization in solution, or by collision induced dissociation (CID) in the gas-phase, using mass spectrometry (MS). Here, we report and investigate the surprising double activation of uranyl by an organic ligand, 3,4,3-LI(CAM), leading to the formation of a formal U 6+ chelate in the gas-phase. The cleavage of both uranyl oxo bonds was experimentally evidence d by CID, using deuterium and 18O isotopic substitutions, and by infrared multiple photon dissociation (IRMPD) spectroscopy. Density functional theorymore » (DFT) computations predict that the overall reaction requires only 132 kJ/mol, with the first oxygen activation entailing about 107 kJ/mol. Here, combined with analysis of similar, but unreactive ligands, these results shed light on the chelation-driven mechanism of uranyl oxo bond cleavage, demonstrating its dependence on the presence of ligand hydroxyl protons available for direct interactions with the uranyl oxygens.« less

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