Synthesis and Structures of Plutonyl Nitrate Complexes: Is Plutonium Heptavalent in PuO3(NO3)2– ?

Gas-phase plutonium nitrate anion complexes were produced by electrospray ionization (ESI) of a plutonium nitrate solution. The ESI mass spectrum included species with all four of the common oxidation states of plutonium: Pu(III), Pu(IV), Pu(V), and Pu(VI). Plutonium nitrate complexes were isolated in a quadrupole ion trap and subjected to collision-induced dissociation (CID). CID of complexes of the general formula PuOx(NO3)y– resulted in the elimination of NO2 to produce PuOx+1(NO3)y−1–, which in most cases corresponds to an increase in the oxidation state of plutonium. Plutonyl species, PuVO2(NO3)2– and PuVIO2(NO3)3–, were produced from PuIII(NO3)4– and PuIV(NO3)5–, respectively, by the elimination of two NO2 molecules. CID of PuVIO2(NO3)3– resulted in NO2 elimination to yield PuO3(NO3)2–, in which the oxidation state of plutonium could be VII, a known oxidation state in condensed phase but not yet in the gas phase. Density functional theory confirmed the nature of PuVO2(NO3)2– and PuVIO2(NO3)3– as plu...