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

Abstract

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 PuO x (NO 3 ) y − resulted in the elimination of NO 2 to produce PuO x+1 (NO 3 ) y−1 − , which in most cases corresponds to an increase in the oxidation state of plutonium. Plutonyl species, Pu V

Remarkably High Stability of Late Actinide Dioxide Cations: Extending Chemistry to Pentavalent Berkelium and Californium

“…[12] Am anifestation of the presence of water in the trap is surface-catalyzed hydrolysis of NO 2 to yield HNO 2 and HNO 3 . [13] The presence of HNO 2 was confirmed by its addition to PuO(NO 3 ) 3 À ,p roduced as described previously, [14] to yield Pu(OH)(NO 2 )(NO 3 ) 3 À .A lthough the presence of HNO 3 was not similarly demonstrated by the appearance of Pu(OH)(NO 3 ) 4 À ,t his negative result does not exclude HNO 3 as a possible reactant gas in the ion trap.…”

“…Each of the MO + was isolated by ejection of all other ions from the QIT andt hen exposed to an indeterminate but constantp ressure of NO 2 for reactiont imes ranging from 0.05 to 0.55 s. The resultsa re shown in Figure 1w here it is apparent that each of the five studied monoxide cations abstracted an oxygen atom to yield MO 2 + .T he formationo ft he dioxides occurs by O-atom abstraction from some neutrals pecies RO in the ion trap under thermal conditions:M O + + RO! MO 2 + + R. As noted below,a nd expected based on the presence of H 2 Oi nt he ion trap, [12,13] hydrolysis of NO 2 yielded HNO 2 ,a sd emonstrated by its addition [14] to PuO(NO 3 ) 3 À to yield Pu(OH)(NO 2 )(NO 3 ) À .I tc an be inferredt hat HNO 3 was also produced, [13] and it is known that O 2 is also present in the trap. [12] The bond dissociation energies (D) for abstraction of an Oatom from the various neutralR Om olecules (potentially)p resent in the ion trap are as follows (in kcal mol À1 ): [15] …”

“…The 249 Bk supplied by Oak Ridge National Laboratory as solid BkCl 3 was dissolved to ac oncentration of 10 mm in ethanol/water.A tt he time of the experiments the 249 Bk, which has a320 day half-life, had partially beta-decayed to yield % 7.6 %o fp rogeny 249 Cf impurity, which is practically isobaric and indistinguishable except by highresolution mass spectrometry.F or all the metals, dilution yielded an ESI solution of % 100 mm metal ion in % 80 %e thanol and % 20 %w ater.A 242 Pu nitrate solution was prepared as described previously to monitor the presence of HNO 2 in the quadrupole ion trap mass spectrometer (QIT/MS). [14] The ESI mass spectrometry experiments were performed using an Agilent 6340 QIT/MS. The containment of the ESI source in ar adiological glove box enables handling of highly radioactive isotopes such as 242 Pu, 243 Am, 249 Bk and 249 Cf.…”

“…The parameters for the PuO(NO 3 ) 3 À calibration experiments were described previously. [14] High-purity nitrogen gas for nebulization and drying in the ion transfer capillary was supplied from the boil-off of al iquid nitrogen Dewar.T he helium buffer gas pressure in the trap is constant at % 10 À4 torr.…”

“…In contrast, the lowest energy structure of CmO 2 + is ah ighly bent peroxide h 2 -structure in which the oxidation state is 5f 7 Cm III .F or BkO 2 + and CfO 2 + the actinyl(V) structures are somewhat more stable than the An III peroxides, and for EsO 2 + the Es V structure is slightly more stable than the Es II superoxide. Beginning with FmO 2 + the An II superoxides become more stable, with the trivalent peroxide the most stable in the case of Lr due to the stability of closed-shell 5f 14 Lr III .…”