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

Abstract

Fragmentation of actinyl(VI) complexes U(VI)O2(L)2(2+), Np(VI)O2(L)2(2+), and Pu(VI)O2(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 U(VI)O2(L)(L-86)(+) with charge reduction, and Np(VI)O2(L)(L-101)(2+) and Pu(VI)O2(L)(L-101)(2+) with charge conservation. The neptunyl and plutonyl complexes also exhibited substantial L(+) loss to give pentavalent complexes Np(V)O2(L)(+) and Pu(V)O2(L)(+), whereas the uranyl complex did not, consistent with the comparative An 5f-orbital energies and the An(VI)O2(2+)/An(V)O2(+) (An = U, Np, Pu) reduction potentials. CID of Np(V)O2(L)2(+) and Pu(V)O2(L)2(+) was dominated by neutral ligand loss to form Np(V)O2(L)(+) and Pu(V)O2(L)(+), which hydrated by addition of residual water in the ion trap; U(V)O2(L)2(+) was not observed. Theoretical calculations of the structures and bonding of the An(VI)O2(L)2(2+) complexes using density functional theory reveal that the metal centers are coordinated by six oxygen atoms from two TMOGA ligands.