Gas Phase Uranyl Activation: Formation of a Uranium Nitrosyl Complex from Uranyl Azide

Activation of the oxo bond of uranyl, UO22+ Was achieved by collision induced dissociation (CID) of UO2(N-3)Cl-2(-) in a quadrupole ion trap mass spectrometer. The gas phase complex UO2(N-3)Cl-2(-) was produced by,electrospray ionization of solutions of UO2Cl2 and NaN3. CID of UO2(N-3)Cl-2(-) resulted in the loss of N-2 to form UO(NO)Cl-2(-), in which the "inert" uranyl oxo bond has been activated. Formation of UO2Cl2: via N-3 loss was also observed. Density functional theory computations predict that the UO(NO)Cl-2(-) complex has nonplanar C-s symmetry and a singlet ground state. Analysis of the bonding of the UO(NO)Cl-2(-) Complex shows that the side-on bonded NO moiety can be considered as NO3-, suggesting a formal oxidation state of U(VI). Activation of the uranyl oxo bond in UO2(N-3)Cl-2(-) to form UO(NO)Cl-2(-) and N-2 was computed to be endothermic by 169 kJ/mol, which is energetically more favorable than formation of NUOCl2- and UO2Cl2-. The observation of UO2Cl2- during CID is most likely due to the absence of an energy barrier for neutral ligand loss.