The actinides exhibit rich redox chemistry, displaying oxidation states from II to VII in solids and/or solutions. Although exotic oxidation states such as Pu(VIII) have been claimed in gas-phase species, such assignments are generally based on indirect and insufficient proof. In recent work we have obtained evidence for a particularly low oxidation state, Cf(II), and an unusually high oxidation state, Np(VII), in gas-phase complexes. Divalent Cf was established by collision induced dissociation of a trivalent methanesulfonate complex. Comparison of the observed fragmentation pathways with those for other actinides and lanthanides indicates reduction from Cf(III) to Cf(II). Heptavalent Np was ascertained from the disparate reactivities of AnO3(NO3)2- for An = U, Np, Pu. Density functional theory computations are in accord with empirical evidence for Np(VII) in the NpO3+ core of NpO3(NO3)2-, while U and Pu are hexavalent in UO3(NO3)2- and PuO3(NO3)2-. Gas-phase chemistry is proving to be a fertile realm to explore the stabilities of oxidation states of the actinides, including that of Bk(IV). The work of JKG, PDD and DKS was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Heavy Element Chemistry, at LBNL under Contract No. DE-AC02-05CH11231.

Actinide redox chemistry in the gas phase: From Cf(II) to Np(VII)

251st National Meeting (2016)

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