Experimental and Theoretical Studies on the Fragmentation of Gas-Phase Uranyl-, Neptunyl-, and Plutonyl-Diglycolamide Complexes

Fragmentation of actinyl(VI) complexes (UO2)-O-VI(L)(2)(2+), (NpO2)-O-VI(L)(2)(2+), and (PuO2)-O-VI(L)(2)(2+) (L = tetramethyl-3-oxa-glutaramide, TMOGA) produced by electrospray ionization was examined in the gas phase by collision induced dissociation (CID) in a quadrupole ion trap mass spectrometer. Cleavage of the C-O-ether bond was observed for all three complexes, with dominant products being (UO2)-O-VI(L)(L-86)(+) with charge reduction, and NPv102(L)(1--101)2+ and (PuO2)-O-VI(L)(L-101)(2+) with charge conservation. The neptunyl and plutonyl complexes also exhibited substantial L+ loss to give pentavalent complexes (NpO2)-O-V(L)(+) and (PuO2)-O-V(L)(+), whereas the uranyl complex did not, consistent with the comparative An 5f-orbital energies and the An(VI)O(2)(2+)/An(V)O(2)(+) (An = U, Np, Pu) reduction potentials. CID of (NpO2)-O-V(L)(2)(+) and (PuO2)-O-V(L)(2)(+) was dominated by neutral ligand loss to form (NpO2)-O-V(L)(+) and (PuO2)-O-V(L)(+), which hydrated by addition of residual water in the ion trap; (UO2)-O-V(L)(2)(+) was not observed. Theoretical calculations of the structures and bonding of the An(VI)O(2)(L)(2)(2+) complexes using density functional, theory reveal that the metal centers are coordinated by six oxygen atoms from two TMOGA ligands.