Oxidation of Gas-Phase Protactinium Ions, Pa⁺ and Pa²⁺:  Formation and Properties of PaO₂²⁺(g), Protactinyl

Abstract

Oxidation reactions of bare and ligated, monopositive, and dipositive Pa ions in the gas phase were studied by Fourier transform ion cyclotron resonance mass spectrometry. Seven oxidants were employed, ranging from the thermodynamically robust N(2)O to the relatively weak CH(2)O-all oxidized Pa(+) to PaO(+) and PaO(+) to PaO(2)(+). On the basis of experimental observations, it was established that D[Pa(+)-O] and D[OPa(+)-O] > or = 751 kJ mol(-1). Estimates for D[Pa(+)-O], D[OPa(+)-O], IE[PaO], and IE[PaO(2)] were also obtained. The seven oxidants reacted with Pa(2+) to produce PaO(2+), indicating that D[Pa(2+)-O] > or = 751 kJ mol(-1). A particularly notable finding was the oxidation of PaO(2+) by N(2)O to PaO(2)(2+), a species, which formally comprises Pa(VI). Collision-induced dissociation of PaO(2)(2+) suggested the protactinyl connectivity, {O-Pa-O}(2+). The experimentally determined IE[PaO(2)(+)] approximately 16.6 eV is in agreement with self-consistent-field and configuration interaction calculations for PaO(2)(+) and PaO(2)(2+). These calculations provide insights into the electronic structures of these ions and indicate the participation of 5f orbitals in bonding and a partial "6p hole" in the case of protactinyl. It was found that PaO(2)(2+) catalyzes the oxidation of CO by N(2)O-such O atom transport via a dipositive metal oxide ion is distinctive. It was also observed that PaO(2)(2+) is capable of activating H(2) to form the stable PaO(2)H(2+) ion.

Gas-Phase Oxidation of Cm+ and Cm2+ − Thermodynamics of Neutral and Ionized CmO

“…Estimates for the IE[MO + ] are based on comparison with electron-transfer efficiencies for selected bare "calibration" M 2+ ions (M = Sn, Pb, Mn, Ge, Bi). These latter efficiencies for the "calibration" M 2+ ions, reported previously [13,14], are summarized in Table 8. The results in Table 8 suggest that the thermodyanmic onset for electron transfer occurs in the approximate range of 1 eV (from the Pb 2+ /CO reaction) and 1.2 eV (from the Pb/CO2 reaction), which is in accord with the estimate of ~1 eV given by Roth and Freiser [50].…”

“…These cycles were explicitly demonstrated by the procedure described in detail previously for the analogous catalytic cycle mediated by PaO2 2+ [14]. Briefly, the M 2+ ions were exposed to a mixture of N2O and CO, the MO 2+ product from Eqn.…”

Elucidating Protactinium Hydrolysis: The Relative Stabilities of PaO2(H2O)+ and PaO(OH)2+

“…46 The formation and thermodynamic characterization of small protactinium oxide molecules have been reported. 43,48−52 It is thus seemingly enigmatic that in the condensed phase, protactinium evidently appears as mono-oxo rather than a dioxo species; 8,17 PaO 2 + exhibits strong Pa−O bonds that are unusually susceptible to activation, as in hydrolysis.…”

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

“…Acentral goal of the present work is to evaluate the intrinsic stabilities of the actinyl(V) cations in the gas phase,a bsent potentially destructive effects in aqueouss olution and other condensed phase environments. Gas-phase actinided ioxidec ations, AnO 2 + ,h ave been reportedf or An = Pa, [8] U, [9] Np, [9] Pu, [9] Am, [10] ,a nd Cm. [11] Each of theseA nO 2 + ions was produced by the sequential gas-phase reactions of the bare An + ions with neutral O-atom donorm olecules, to first yield AnO + and then AnO 2 + .A na im of the presentw ork is to extend this chemistry furtheri nto the actinides eries, to BkO 2 + and CfO 2 + .A lthough neither berkelyl(V) nor californyl(V) are stable in the condensed phase,i ti sf easible that they are stable as isolated gas-phase species,ina nalogy with the PrO 2 + molecular ion, am oiety that is not knowni nc ondensed phase chemistry.I np arallel with the synthesis of new AnO 2 + molecular ions, electronic structure calculations werep erformed at the correlated molecular orbitaltheory coupled clusterC CSD(T) level to assess the structures, including formal actinideo xidation states, for known, new,a nd predicted AnO 2 + gas-phase ions for all of the actinides from Pa throughL r. The combined experiment and computational resultsp rovide evidence for the synthesis of two new prototypical actinyl(V) molecules, BkO 2 + andC fO 2 + ,a nd furthermore present an evaluation of the variations in stability of actinyl(V) ions, [O=An=O] + ,a cross the series and the prospects for producing EsO 2 + and actinyls of even heavierm embers of the series.…”