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Conversion of a UO22+ Precursor to UH+ and U+ Using Tandem Mass Spectrometry to Remove Both “yl” Oxo Ligands
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Journal of the American Society for Mass Spectrometry

Cite this: J. Am. Soc. Mass Spectrom. 2023, 34, 11, 2439–2442
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https://doi.org/10.1021/jasms.3c00260
Published October 16, 2023

Copyright © 2023 The Authors. Published by American Chemical Society. This publication is licensed under

CC-BY 4.0 .

Abstract

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Multiple-stage collision-induced dissociation (CID) of a uranyl propiolate cation, [UO2(O2C–C≡CH)]+, can be used to prepare the U-methylidyne species [O═U≡CH]+ [J. Am. Soc. Mass Spectrom. 2019, 30, 796–805]. Here, we report that CID of [O═U≡CH]+ causes elimination of CO to create [UH]+, followed by a loss of H• to generate U+. A feasible, multiple-step pathway for the generation of [UH]+ was identified using DFT calculations. These results provide the first demonstration that multiple-stage CID can be used to prepare both U+ and UH+ directly from a UO22+ precursor for the subsequent investigation of ion–molecule reactivity.

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Introduction

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The high stability and inertness of U═O bonds make activation and/or functionalization of UO22+ and UO2+ challenging. (1−6) There is ample evidence that U═O bonds can be activated and substituted using collision-induced dissociation (CID) in multidimensional (MSn) tandem MS experiments. (7−14) Recently, we showed that CID of the organometallic species [UO2(C≡CH)]+ induces the elimination of CO to furnish [OUCH]+. (12) Density functional theory (DFT) calculations strongly supported the conclusion that the [OUCH]+ ion is an oxouranium-methylidyne ([O═U≡CH]+) product.
In general, the formation of [O═U≡CH]+ is important because it might be used as an intermediate to prepare new U-containing ions for the investigation of intrinsic structure, bonding, and reactivity. As we describe below, the CID of the methylidyne species causes elimination of CO to create [UH]+. An additional dissociation step causes the elimination of H• to generate U+. To the best of our knowledge, this is the first demonstration that the stable UO22+ ion can be converted to low oxidation state species such as [UH]+ and subsequently U+ for studies of intrinsic reactivity using an ion trap mass spectrometer.

Experimental and Computational

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Generation of [O═U≡CH]+ using MSn has been described in detail elsewhere, (12) and the experimental and computational details are provided in the Supporting Information. Briefly, [UO2(O2C–C≡CH)(CH3OH)2]+ was created by electrospray ionization (ESI), and the CH3OH ligands were eliminated in sequential CID steps (MS2 and MS3). Decarboxylation of [UO2(O2C–C≡CH)]+ to create [UO2(C≡CH)]+ (MS4) was followed by generation of [O═U≡CH]+ by elimination of CO (MS5, Figure 1a).

Figure 1

Figure 1. Product ion spectra generated by MSn of [UO2(O2C≡CH)]+ precursor: (a) CID (MS5 stage) of [UO2C≡CH]+, (b) CID (MS6 stage) of [OUCH]+ and (c) CID (MS7 stage) of [UH]+. m/z values in bold represent precursor ions; those that are italicized are product ions. Normalized collision energies (NCE) used at each MSn stage are provided in each spectrum.

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Results

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The product ion spectrum generated by collisional activation of [O═U≡CH]+ (m/z 267, MS5 stage) is shown in Figure 1b. The base peak appeared at m/z = 239, corresponding to the elimination of 28 Da from [O═U≡CH]+. Because the composition of the ion at m/z 267 was confirmed as [OUCH]+ by high-resolution mass measurement, (12) a loss of 28 Da is logically attributed to the elimination of CO to yield [UH]+ at m/z 239. Subsequent CID of [UH]+ at m/z 239 (MS6 stage) causes the elimination of 1 Da (H•) to generate U+ at m/z 238 (Figure 1c). When including the loss of CO observed during production of [OUCH]+ from [UO2(C≡CH)]+, the results shown in Figure 1a demonstrate that both “yl” oxo ligands of UO22+ can be eliminated in a multiple-stage CID experiment.
Also observed in the CID spectrum of [O═U≡CH]+ (Figure 1b) were peaks at m/z 254 and 255, which are assigned as [UO]+ and [UOH]+, respectively, likely created by ion–molecule reactions of [UH]+ and/or U+ with background H2O and O2 present in the ion trap during CID. To test this hypothesis, the ions at m/z 239 and 238 were independently isolated, held in the ion trap for 100 ms, and allowed to react with adventitious neutrals (typically H2O and O2). As shown in Figure 2a, isolation of [UH]+ at m/z 239 leads to the formation of peaks at m/z 254, 255, 270, 271, and 287. Suggested reaction pathways are summarized in Scheme S1. Formation of the product ion at m/z 271 is attributed to the reaction of [UOH]+ with O2 to generate [UO2H]+, while a subsequent reaction with adventitious H2O would lead to the formation of [UO2OH]+ and (neutral) H2. Isolation instead of U+ at m/z 238 for 100 ms (Figure 2b) yielded product ions at m/z 254 ([UO]+) and 270 (UO2+) and proposed pathways are summarized in Scheme S2. The tendency to react with O2 was probed using 18O2 labeled gas, which was deliberately introduced into the ion trap. We note that the product ions reported here for U+ are consistent with earlier studies. (15,16) To the best of our knowledge, the intrinsic reactions of [UH]+ have yet to be studied and will be investigated by our laboratory in the future.

Figure 2

Figure 2. Product ion spectra generated by the isolation and storage of (a) [UH]+ and (b) U+, without imposed collisional activation, in the ion trap for 100 ms. m/z values in bold represent precursor ions; those that are italicized are product ions.

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Reaction energy profiles (thermally corrected enthalpies of singlet-, triplet-, and quintet-state species) generated at the B3LYP level of theory (computational methodology is provided in the SI) for dissociation of [O═U≡CH]+ are shown in Figure 3 (PBE0 data are provided in the Supporting Information). Calculations suggest that the formation of [UH]+ proceeds through a multiple-step mechanism initiated from [O═U≡CH]+ in the singlet spin state. The computed energy of the [O═U≡CH]+ precursor (I) in the singlet state was lower than that in the triplet state by ca. 74 kJ/mol. A crossing to the triplet surface occurs prior to the first transition state (TSI → II) to create an [O-UH-C]+ insertion intermediate (II). Rearrangement continues through TSII → III, to create a second intermediate, [UH(CO)]+ (III). Structures for I, TSI → II, II, and TSII → III failed to converge in the quintet spin state. However, III and [UH]+ (IV) have similar energies in the triplet and quintet states, and separation of III into [UH]+ (IV) was computed to require 34 and 77 kJ/mol on the triplet and quintet surfaces, respectively. An important benchmark for our study is the report by Armentrout and co-workers that the ground state of [UH]+, created using reaction of U+ with H2, is the quintet, (17) with a U–H bond dissociation energy of 252.199 kJ/mol (without spin–orbit correction) compared to an experimental value of 239.270 (±5.789) kJ/mol. As a benchmark for our computational work, independent calculation of the U–H (quintet state) BDE in this study yielded a value of 254.369 kJ/mol, which is in reasonable agreement with the value of Armentrout and co-workers. (17)

Figure 3

Figure 3. Reaction energy diagram (298 K) for the generation of [UH]+ from [OUCH]+. Relative energies for species in a singlet spin state indicated by blue symbols and lines; black symbols and lines indicate species in the triplet spin state, and red indicates the quintet states of the final two species.

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The importance of “two-state reactivity” in gas-phase organometallic chemistry (18) and the chemistry of electronic excited states (19) has been summarized elsewhere, and the crossings of energy profiles for different spin states are consistent with our earlier studies with gas-phase U species, including (7) the formation of [NUO]+ from [UO2(C≡N)]+ and generation of [O═U≡CH]+ from the CID of [UO2(C≡CH)]+. (14) While spin–orbit effects were not included in our computed reaction energetics, a previous experimental and computational study of the U–H bond dissociation energy (17) have shown that spin–orbit corrections can lower the energies of [UH]+ and U+ by 0.779 eV (75.2 kJ/mol) and 0.852 eV (85.2 kJ/mol), respectively. Based on previous reports, (20−25) we expect that spin–orbit effects for the U 5f orbitals could enhance the coupling between the singlet, triplet, and quintet potential energy surfaces. (26)

Conclusion

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To summarize, CID of an [O═U≡CH]+ intermediate causes elimination of CO to create [UH]+ and H• to form U+. This remarkable outcome further illustrates the advantage of using MSn to remove both “yl” oxo ligands of the uranyl ion. DFT calculations provide a reasonable, multiple-step pathway with crossing from the singlet to triplet surface to explain the formation of the uranium hydride cation. To date, U+ has been formed using discharge or laser ablation sources to great effect (15,16,27,28) and UH+ by the reaction of U+ with H2 or hydrocarbons. (17,29,30) Our results show that the MSn experiment effectively converts the stable uranyl dication to [UH]+ and U+ for investigation of ion–molecule reactivity using ion trap mass MS, thus broadening the range of species that can be created and accessed using conventional instruments equipped with ESI sources. Reliable formation of [UH]+ is important given the interest in actinide hydrides in catalysis and the need to understand the behavior of uranium hydrides in the context of safe storage of spent nuclear fuels.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jasms.3c00260.

  • Reaction energy diagram (PBE0 level of theory) for the generation of [UH]+ from [OUCH]+; proposed pathways for the reaction of [UH]+ and U+ with (neutral) O2 and H2O; experimental and computational methods; Cartesian coordinates for precursor, intermediate, and transition state structures; electronic energies and thermally corrected enthalpies for all species (PDF)

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Author Information

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  • Corresponding Author
  • Authors
    • Justin G. Terhorst - Department of Chemistry, Duquesne University, 600 Forbes Avenue, Pittsburgh, Pennsylvania 15282, United States
    • Theodore A. Corcovilos - Department of Physics, Duquesne University, 600 Forbes Avenue, Pittsburgh, Pennsylvania 15282, United States;  Orcidhttps://orcid.org/0000-0001-5716-1188
  • Author Contributions

    The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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This work was supported by the National Science Foundation (CHE-1726824) and the Robert Dean Loughney Faculty Development Endowment of Duquesne University.

References

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This article references 30 other publications.

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    Abergel, Rebecca J.; de Jong, Wibe A.; Deblonde, Gauthier J.-P.; Dau, Phuong D.; Captain, Ilya; Eaton, Teresa M.; Jian, Jiwen; van Stipdonk, Michael J.; Martens, Jonathan; Berden, Giel; Oomens, Jos; Gibson, John K.
    Inorganic Chemistry (2017), 56 (21), 12930-12937CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    Recent efforts to activate the strong uranium-oxygen bonds in the dioxo uranyl cation have been limited to single oxo-group activation through either uranyl redn. and functionalization in soln., or by collision induced dissocn. (CID) in the gas-phase, using mass spectrometry (MS). Here, we report and investigate the surprising double activation of uranyl by an org. ligand, 3,4,3-LI(CAM), leading to the formation of a formal U6+ chelate in the gas-phase. The cleavage of both uranyl oxo bonds was exptl. evidenced by CID, using deuterium and 18O isotopic substitutions, and by IR multiple photon dissocn. (IRMPD) spectroscopy. D. functional theory (DFT) computations predict that the overall reaction requires only 132 kJ/mol, with the first oxygen activation entailing about 107 kJ/mol. Combined with anal. of similar, but unreactive ligands, these results shed light on the chelation-driven mechanism of uranyl oxo bond cleavage, demonstrating its dependence on the presence of ligand hydroxyl protons available for direct interactions with the uranyl oxygens.
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  11. 11
    Hu, S.-X.; Jian, J.; Li, J.; Gibson, J. K. Destruction of the Uranyl Moiety in a U(V) “Cation–Cation” Interaction. Inorg. Chem. 2019, 58 (15), 10148– 10159,  DOI: 10.1021/acs.inorgchem.9b01265
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    11
    Destruction of the Uranyl Moiety in a U(V) "Cation-Cation" Interaction
    Hu, Shu-Xian; Jian, Jiwen; Li, Jun; Gibson, John K.
    Inorganic Chemistry (2019), 58 (15), 10148-10159CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    A gas-phase uranyl peroxide dimer supported by three 12-crown-4 ether (12C4) ligands, [(UO2)2(O2)(12C4)3]2+ (A), was prepd. by electrospray ionization. D. functional theory (DFT) indicates a structure with two terminal 12C4 and the third 12C4 bridging the uranium centers. Collision induced dissocn. (CID) of A resulted in elimination of the bridging 12C4 to yield a uranyl peroxide dimer with two terminal donor ligands, [(12C4)(UO2)(O2)(UO2)(12C4)]2+ (B). Remarkably, CID of B resulted in elimination of the bridging peroxide concomitant with redn. of U(VI) to U(V) in C, [(12C4)(UO2)(UO2)(12C4)]2+. DFT studies indicate that in C there is direct interaction between the two UO2+ species, which can thus be considered as a so-called cation-cation interaction (CCI). This formal CCI, induced by tetradentate 12C4 ligands, corresponds to destruction of the linear uranyl moieties and creation of bridging U-O-U oxo-bonds. On the basis of the structural rearrangement to achieve the structurally extreme CCI interaction, it is predicted also to be accessible for PaO2+ but is less feasible for transuranic actinyls.
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  12. 12
    Van Stipdonk, M. J.; Tatosian, I. J.; Iacovino, A. C.; Bubas, A. R.; Metzler, L. J.; Sherman, M. C.; Somogyi, A. Gas-Phase Deconstruction of UO22+: Mass Spectrometry Evidence for Generation of [OUVICH]+ by Collision-Induced Dissociation of [UVIO2 (C≡CH)]+. J. Am. Soc. Mass Spectrom. 2019, 30 (5), 796– 805,  DOI: 10.1007/s13361-019-02179-6
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    12
    Gas-Phase Deconstruction of UO22+: Mass Spectrometry Evidence for Generation of [OUVICH]+ by Collision-Induced Dissociation of [UVIO2(C≃CH)]+
    van Stipdonk, Michael J.; Tatosian, Irena J.; Iacovino, Anna C.; Bubas, Amanda R.; Metzler, Luke J.; Sherman, Mary C.; Somogyi, Arpad
    Journal of the American Society for Mass Spectrometry (2019), 30 (5), 796-805CODEN: JAMSEF; ISSN:1044-0305. (Springer)
    Because of the high stability and inertness of the U:O bonds, activation and/or functionalization of UO22+ and UO2+ remain challenging tasks. We show here that collision-induced dissocn. (CID) of the uranyl-propiolate cation, [UVIO2(O2C-C≃CH)]+, can be used to prep. [UVIO2(C≃CH)]+ in the gas phase by decarboxylation. Remarkably, CID of [UVIO2(C≃CH)]+ caused elimination of CO to create [OUVICH]+, thus providing a new example of a well-defined substitution of an "yl" oxo ligand of UVIO22+ in a unimol. reaction. Relative energies for candidate structures based on d. functional theory calcns. suggest that the [OUVICH]+ ion is a uranium-methylidyne product, with a U≃C triple bond composed of one σ-bond with contributions from the U df and C sp. hybrid orbitals, and two π-bonds with contributions from the U df and C p orbitals. Upon isolation, without imposed collisional activation, [OUVICH]+ appears to react spontaneously with O2 to produce [UVO2]+.
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  13. 13
    Metzler, L. J.; Farmen, C. T.; Corcovilos, T. A.; Van Stipdonk, M. J. Intrinsic Chemistry of [OUCH]+: Reactions with H2O, CH3C≡N and O2. Phys. Chem. Chem. Phys. 2021, 23 (8), 4475– 4479,  DOI: 10.1039/D1CP00177A
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    13
    Intrinsic chemistry of [OUCH]+: reactions with H2O, CH3CΞN and O2
    Metzler, Luke J.; Farmen, Christopher T.; Corcovilos, Theodore A.; Van Stipdonk, Michael J.
    Physical Chemistry Chemical Physics (2021), 23 (8), 4475-4479CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    We report the first exptl. study of the intrinsic chem. of a U-methylidyne species, focusing on reaction of [OUCH]+ with H2O, O2 and CH3CΞN in the gas phase. DFT was also used to det. reaction pathways, and establish the mechanism by which [OUCH]+ is formed through collision-induced dissocn. of [UO2(CΞCH)]+.
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  14. 14
    Van Stipdonk, M. J.; Perez, E. H.; Metzler, L. J.; Bubas, A. R.; Corcovilos, T.; Somogyi, A. Destruction and Reconstruction of UO22+ Using Gas-Phase Reactions. Phys. Chem. Chem. Phys. 2021, 23 (20), 11844– 11851,  DOI: 10.1039/D1CP01520F
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    14
    Destruction and reconstruction of UO22+ using gas-phase reactions
    Van Stipdonk, Michael J.; Perez, Evan H.; Metzler, Luke J.; Bubas, Amanda R.; Corcovilos, Theodore; Somogyi, Arpad
    Physical Chemistry Chemical Physics (2021), 23 (20), 11844-11851CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    While the strong axial UO bonds confer high stability and inertness to UO22+, it has been shown that the axial oxo ligands can be eliminated or replaced in the gas-phase using collision-induced dissocn. (CID) reactions. We report here tandem mass spectrometry expts. initiated with a gas-phase complex that includes UO22+ coordinated by a 2,6-difluorobenzoate ligand. After decarboxylation to form a difluorophenide coordinated uranyl ion, [UO2(C6F2H3)]+, CID causes elimination of CO, and then CO and C2H2 in sequential dissocn. steps, to leave a reactive uranium fluoride ion, [UF2(C2H)]+. Reaction of [UF2(C2H)]+ with CH3OH creates [UF2(OCH3)]+, [UF(OCH3)2]+ and [UF(OCH3)2(CH3OH)]+. Cleavage of C-O bonds within these species results in the elimination of Me cation (CH3+). Subsequent CID steps convert [UF(OCH3)2]+ to [UO2(F)]+ and similarly, [U(OCH3)3]+ to [UO2(OCH3)]+. Our expts. show removal of both uranyl oxo ligands in "top-down" CID reactions and replacement in "bottom-up" ion-mol. and dissocn. steps.
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  15. 15
    Armentrout, P.; Beauchamp, J. Reactions of U+ and UO+ with O2, CO, CO2, COS, CS2 and D2O. Chem. Phys. 1980, 50 (1), 27– 36,  DOI: 10.1016/0301-0104(80)87022-4
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    Reactions of uranium(1+) and uranium monoxide(1+) ions with diatomic oxygen, carbon monoxide, carbon dioxide, carbon oxide sulfide, carbon disulfide and water-d2
    Armentrout, P. B.; Beauchamp, J. L.
    Chemical Physics (1980), 50 (1), 27-36CODEN: CMPHC2; ISSN:0301-0104.
    An ion-beam app. was used to study the reactions of U+ and UO+ with O2, CO, CO2, COS, CS2, and D2O. Reaction cross sections as functions of the ion kinetic energy were detd. and compared to simple models for exothermic and endothermic reactions. With 2 exceptions, all exothermic reactions exhibited large cross sections that decreased with increasing kinetic energy. The reactions of UO+ with CO2 and COS to form UO2+ exhibited substantial energy barriers; U+ reacted with CO to yield both UO+ and UC+ in endothermic processes. The thresholds for these reactions agree well with literature thermochem.
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  16. 16
    Jackson, G. P.; King, F. L.; Goeringer, D. E.; Duckworth, D. C. Gas-Phase Reactions of U+ and U2+ with O2 and H2O in a Quadrupole Ion Trap. J. Phys. Chem. A 2002, 106 (34), 7788– 7794,  DOI: 10.1021/jp0259420
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    16
    Gas-Phase Reactions of U+ and U2+ with O2 and H2O in a Quadrupole Ion Trap
    Jackson, Glen P.; King, Fred L.; Goeringer, Douglas E.; Duckworth, Douglas C.
    Journal of Physical Chemistry A (2002), 106 (34), 7788-7794CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
    Reaction pathways and rate consts. of gas-phase uranium and uranium oxide ions with O2 and H2O have been investigated using a quadrupole ion trap mass spectrometer (QIT-MS). A new reaction pathway is identified for the reaction between U2+ and H2O, which leads to the formation of UO+ via the intermediate UOH2+. Reaction rate consts. are detd. for several reactions by measuring the reaction rate at different partial pressures of the reagent gas and are found to be in reasonable agreement with the literature. These rate consts. include the first known measurement for the reaction of U2+ with H2O (∼0.4 kADO). New limits on thermochem. values are also provided for certain species. These include ΔHf (UO2+) ≤ 1742 kJ mol-1 and 1614 ≤ ΔHf (UOH2+) ≤ 1818 kJ mol-1 and are based on the assumption that only exothermic or thermoneutral reactions are possible under the conditions used. This assumption is supported by simulations of the root-mean-square (RMS) ion kinetic energy of stored uranium ions in the QIT. Only a slight increase in the RMS ion kinetic energies, from 0.1 to 0.2 eV, is predicted over the range of trapping conditions studied (0.05 ≤ qz ≤ 0.75) corresponding to a theor. reaction temp. of ∼384 K. The simulations also compare helium and neon as bath gases and show that the RMS kinetic energies are found to be very similar at long trapping times (>20 ms), although neon establishes steady state conditions in approx. half the time.
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  17. 17
    Zhang, W.-J.; Demireva, M.; Kim, J.; de Jong, W. A.; Armentrout, P. Reactions of U+ with H2, D2, and HD Studied by Guided Ion Beam Tandem Mass Spectrometry and Theory. J. Phys. Chem. A 2021, 125 (36), 7825– 7839,  DOI: 10.1021/acs.jpca.1c05409
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    Reactions of U+ with H2, D2, and HD Studied by Guided Ion Beam Tandem Mass Spectrometry and Theory
    Zhang, Wen-Jing; Demireva, Maria; Kim, JungSoo; de Jong, Wibe A.; Armentrout, P. B.
    Journal of Physical Chemistry A (2021), 125 (36), 7825-7839CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
    The kinetic energy-dependent reactions of the at. actinide uranium cation (U+) with H2, D2, and HD were examd. by guided ion beam tandem mass spectrometry. An av. 0 K bond dissocn. energy of D0(U+ - H) = 2.48 ± 0.06 eV is obtained by anal. of the endothermic product ion cross sections. Quantum chem. calcns. were performed for comparison with exptl. thermochem., including high-level CASSCF-CASPT2-RASSI calcns. of the spin-orbit corrections. CCSD(T) and the CASSCF levels show excellent agreement with expt., whereas B3LYP and PBE0 slightly overestimate and the M06 approach badly underestimates the bond energy for UH+. Theory was also used to investigate the electronic structures of the reaction intermediates and potential energy surfaces. The exptl. product branching ratio for the reaction of U+ with HD indicates that these reactions occur primarily via a direct reaction mechanism, despite the presence of a deep-well for UH2+ formation according to theory. The reactivity and hydride bond energy for U+ are compared with those for transition metal, lanthanide, and actinide cations, and periodic trends are discussed. These comparisons suggest that the 5f electrons on uranium are largely core and uninvolved in the reactive chem.
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    Schröder, D.; Shaik, S.; Schwarz, H. Two-State Reactivity as a New Concept in Organometallic Chemistry. Acc. Chem. Res. 2000, 33 (3), 139– 145,  DOI: 10.1021/ar990028j
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    Two-state reactivity as a new concept in organometallic chemistry
    Schroder D; Shaik S; Schwarz H
    Accounts of chemical research (2000), 33 (3), 139-45 ISSN:0001-4842.
    It is proposed that spin-crossing effects can dramatically affect reaction mechanisms, rate constants, branching ratios, and temperature behaviors of organometallic transformations. This phenomenon is termed two-state reactivity (TSR) and involves participation of spin inversion in the rate-determining step. While the present analysis is based on studies of transition metals under idealized conditions, several recent reports imply that TSR is by no means confined to the gas phase. In fact, participation of more than a single spin surface in the reaction pathways is proposed as a key feature in organometallic chemistry.
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    Armentrout, P. B. Chemistry of Excited Electronic States. Science 1991, 251 (4990), 175– 179,  DOI: 10.1126/science.251.4990.175
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    Chemistry of excited electronic states
    Armentrout, P. B.
    Science (Washington, DC, United States) (1991), 251 (4990), 175-9CODEN: SCIEAS; ISSN:0036-8075.
    A review with 34 refs on at. and MO applications in chem.
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    Kaltsoyannis, N. Transuranic Computational Chemistry. Chem.─Eur. J. 2018, 24 (12), 2815– 2825,  DOI: 10.1002/chem.201704445
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    Transuranic Computational Chemistry
    Kaltsoyannis, Nikolas
    Chemistry - A European Journal (2018), 24 (12), 2815-2825CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. Recent developments in the chem. of the transuranic elements are surveyed, with particular emphasis on computational contributions. Examples are drawn from mol. coordination and organometallic chem., and from the study of extended solid systems. The role of the metal valence orbitals in covalent bonding is a particular focus, esp. the consequences of the stabilization of the 5f orbitals as the actinide series is traversed. The fledgling chem. of transuranic elements in the +II oxidn. state is highlighted. Throughout, the symbiotic interplay of exptl. and computational studies is emphasized; the extraordinary challenges of exptl. transuranic chem. afford computational chem. a particularly valuable role at the frontier of the periodic table.
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    Pegg, J. T.; Shields, A. E.; Storr, M. T.; Scanlon, D. O.; de Leeuw, N. H. Noncollinear Relativistic DFT + U Calculations of Actinide Dioxide Surfaces. J. Phys. Chem. C 2019, 123 (1), 356– 366,  DOI: 10.1021/acs.jpcc.8b07823
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    Noncollinear Relativistic DFT + U Calculations of Actinide Dioxide Surfaces
    Pegg, James T.; Shields, Ashley E.; Storr, Mark T.; Scanlon, David O.; de Leeuw, Nora H.
    Journal of Physical Chemistry C (2019), 123 (1), 356-366CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    A noncollinear relativistic PBEsol + U study of low-index actinide dioxides (AnO2, An = U, Np, or Pu) surfaces has been conducted. The importance of magnetic vector reorientation relative to the plane of the surface is highlighted; this has often been ignored in collinear nonrelativistic models. The use of noncollinear relativistic methods is key to the design of reliable computational models. The ionic relaxation of each surface is shown to be confined to the first three monolayers, and we have explored the configurations of the terminal oxygen ions on the reconstructed (001) surface. The reconstructed (001) surfaces are ordered as (001)αβ < (001)α < (001)β in terms of energetics. Electrostatic potential isosurface and scanning tunneling microscopy images have also been calcd. By considering the energetics of the low-index AnO2 surfaces, an octahedral Wulff crystal morphol. has been calcd.
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    Wdowik, U. D.; Piekarz, P.; Legut, D.; Jagło, G. Effect of Spin-Orbit and on-Site Coulomb Interactions on the Electronic Structure and Lattice Dynamics of Uranium Monocarbide. Phys. Rev. B 2016, 94 (5), 054303,  DOI: 10.1103/PhysRevB.94.054303
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    Effect of spin-orbit and on-site Coulomb interactions on the electronic structure and lattice dynamics of uranium monocarbide
    Wdowik, U. D.; Piekarz, P.; Legu, D.; Jaglo, G.
    Physical Review B (2016), 94 (5), 054303/1-054303/9CODEN: PRBHB7; ISSN:2469-9950. (American Physical Society)
    Uranium monocarbide, a potential fuel material for the generation IV reactors, is investigated within d. functional theory. Its electronic, magnetic, elastic, and phonon properties are analyzed and discussed in terms of spin-orbit interaction and localized vs. itinerant behavior of the 5f electrons. The localization of the 5f states is tuned by varying the local Coulomb repulsion interaction parameter. We demonstrate that the theor. electronic structure, elastic consts., phonon dispersions, and their densities of states can reproduce accurately the results of x-ray photoemission and bremsstrahlung isochromat measurements as well as inelastic neutron scattering expts. only when the 5f states experience the spin-orbit interaction and simultaneously remain partially localized. The partial localization of the 5f electrons could be represented by a moderate value of the on-site Coulomb interaction parameter of about 2 eV. The results of the present studies indicate that both strong electron correlations and spin-orbit effects are crucial for realistic theor. description of the ground-state properties of uranium carbide.
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    Marian, C. M. Spin–Orbit Coupling and Intersystem Crossing in Molecules. WIREs Comput. Mol. Sci. 2012, 2 (2), 187– 203,  DOI: 10.1002/wcms.83
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    Pereira, C. C. L.; Michelini, M. d. C.; Marcalo, J.; Gong, Y.; Gibson, J. K. Synthesis and Properties of Uranium Sulfide Cations. An Evaluation of the Stability of Thiouranyl, {S = U=S}2+. Inorg. Chem. 2013, 52 (24), 14162– 14167,  DOI: 10.1021/ic4020493
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    Synthesis and Properties of Uranium Sulfide Cations. An Evaluation of the Stability of Thiouranyl, {S=U=S}2+
    Pereira, Claudia C. L.; Michelini, Maria del Carmen; Marcalo, Joaquim; Gong, Yu; Gibson, John K.
    Inorganic Chemistry (2013), 52 (24), 14162-14167CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    Atomic uranium cations, U+ and U2+, reacted with the facile sulfur-atom donor OCS to produce several monopos. and dipos. uranium sulfide species contg. up to four sulfur atoms. Sequential abstraction of two sulfur atoms by U2+ resulted in US22+; d. functional theory computations indicate that the ground-state structure for this species is side-on η2-S2 triangular US22+, with the linear thiouranyl isomer, {S=UVI=S}2+, some 171 kJ mol-1 higher in energy. The result that the linear thiouranyl structure is a local min. at a moderate energy suggests that it should be feasible to stabilize this moiety in mol. compds.
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    Marks, J.; Rittgers, B.; Van Stipdonk, M.; Duncan, M. Photodissociation and Infrared Spectroscopy of Uranium–Nitrogen Cation Complexes. J. Phys. Chem. A 2021, 125 (33), 7278– 7288,  DOI: 10.1021/acs.jpca.1c05823
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    25
    Photodissociation and Infrared Spectroscopy of Uranium-Nitrogen Cation Complexes
    Marks, J. H.; Rittgers, B. M.; Van Stipdonk, M. J.; Duncan, M. A.
    Journal of Physical Chemistry A (2021), 125 (33), 7278-7288CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
    Laser vaporization of uranium in a pulsed supersonic expansion of nitrogen is used to produce complexes of the form U+(N2)n (n = 1-8). These ions are mass selected in a reflectron time-of-flight spectrometer and studied with visible and UV laser fixed-frequency photodissocn. and with tunable IR laser photodissocn. spectroscopy. The dissocn. patterns and spectroscopy of U+(N2)n indicate that N2 ligands are intact mols. and that there is no insertion chem. resulting in UN+ or NUN+. Fixed frequency photodissocn. at 532 and 355 nm indicate that the U+-N2 bond dissocn. energy varies little with changing coordination. The photon energy and the no. of ligands eliminated allow an est. of the av. U+-N2 dissocn. energy of 12 kcal/mol. IR bands are obsd. for these complexes near the N-N stretch vibration via elimination of N2 mols. These resonances are obsd. to be shifted about 130 cm-1 to the red from the free-N2 frequency for complexes with n = 3-8. D. functional theory indicates that U+ is most stable in the sextet state in these complexes and that N2 mols. bind in end-on configurations. The fully coordinated complex is predicted to be U+(N2)8, which has a cubic structure. The vibrational frequencies predicted by theory are consistently lower than those in the expt., independent of the isomeric structure or spin state of the complexes. Despite its failure to reproduce the IR spectra, theory provides an av. U+-N2 dissocn. energy of 11.8 ± 0.5 kcal/mol, in good agreement with the value from the expts.
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    Moreland, P. E., Jr; Rokop, D. J.; Stevens, C. M. Mass-Spectrometric Observations of Uranium and Plutonium Monohydrides Formed by Ion─Molecule Reaction. Int. J. Mass Spectrom. Ion Phys. 1970, 5 (1–2), 127– 136,  DOI: 10.1016/0020-7381(70)87011-5
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    Mass-spectrometric observations of uranium and plutonium monohydrides formed by ion-molecule reactions
    Moreland, Parker E.; Rokop, Donald J.; Stevens, Charles M.
    International Journal of Mass Spectrometry and Ion Physics (1970), 5 (1-2), 127-36CODEN: IJMIBY; ISSN:0020-7381.
    The monohydride ions UH+, UD+, PuH+, and PuD+ were obsd. in the mass spectrum of U and Pu during the isotopic anal. of these metals by surface ionization mass spectrometry. By introducing H and vapors of H compds. into the ion source, the hydrides could be produced by endothermic ion-mol. reactions of the metal-ion beam and residual gases. Hydride product ions were obtained with measurable intensity for the systems: U+ + H2, U+ + D2, U+ + H2O, U+ + D2O, U+ + H2S, Pu+ + H2, Pu+ + D2. Anal. of relatively crude product-ion energy spectra permits the dissociation energy D0(U+ - H) to be estd. at 3.3 ± 0.5 eV. The use of a retarding potential as a high-pass energy filter permits complete rejection of hydride ions in the mass spectrometer, due to the endothermic nature of the reactions involved.
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  1. Samuel J. Lenze, Justin Terhorst, Amina Ihabi, Theodore Corcovilos, Michael J. van Stipdonk. Creation of Gas‐Phase Organo‐Uranium Species by Removal of “yl” Oxo Ligands From UO 2 2+ Carboxylate Precursor Ions. Rapid Communications in Mass Spectrometry 2025, 39 (4) https://doi.org/10.1002/rcm.9954
  2. Justin G. Terhorst, Theodore A. Corcovilos, Samuel J. Lenze, Michael J. van Stipdonk. Synthesis of organo-uranium( ii ) species in the gas-phase using reactions between [UH] + and nitriles. Dalton Transactions 2024, 54 (1) , 231-238. https://doi.org/10.1039/D4DT02508C
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  • Abstract

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    Figure 1

    Figure 1. Product ion spectra generated by MSn of [UO2(O2C≡CH)]+ precursor: (a) CID (MS5 stage) of [UO2C≡CH]+, (b) CID (MS6 stage) of [OUCH]+ and (c) CID (MS7 stage) of [UH]+. m/z values in bold represent precursor ions; those that are italicized are product ions. Normalized collision energies (NCE) used at each MSn stage are provided in each spectrum.

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    Figure 2

    Figure 2. Product ion spectra generated by the isolation and storage of (a) [UH]+ and (b) U+, without imposed collisional activation, in the ion trap for 100 ms. m/z values in bold represent precursor ions; those that are italicized are product ions.

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    Figure 3

    Figure 3. Reaction energy diagram (298 K) for the generation of [UH]+ from [OUCH]+. Relative energies for species in a singlet spin state indicated by blue symbols and lines; black symbols and lines indicate species in the triplet spin state, and red indicates the quintet states of the final two species.

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  • References

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      A review. Uranyl (UO22+) is an exceptionally stable mol. species, characterized by a linear O=U=O geometry and short U-O bonds. Its two oxo ligands are thought to be inert to exchange and resistant to functionalization. However, a growing body of literature suggests that this assessment may need to be reevaluated. This review summarizes the chem. of the two oxo ligands of the uranyl ion. In particular, the authors explore the interaction of the uranyl oxo ligands with Lewis acids, and outline attempts to selectively functionalize the oxo ligands of uranyl by chem. means. The authors also discuss the kinetic and mechanistic knowledge for oxo ligand exchange under acidic, basic and photolytic conditions.
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      A review. The chem. of the uranyl ion ([UO2]2+) has evolved remarkably over the past few years, with unexpected reactivity obsd. that challenge the authors' understanding of this ion, and of actinides in general. This review highlights some recent advances in the field, focussing on the organometallic chem. of the uranyl moiety, which is not well developed in comparison to lower oxidn. states of U. The use of uranyl as a catalyst is highlighted and the newly developed supramol. chem. is described. The uranyl O atoms were considered as inert, but recent work showed that is not necessarily the case and is discussed herein. Finally, redn. to the [UO2]+ ion is discussed.
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      A review. The actinide chem. literature has been particularly vibrant over recent years, esp. for uranium and thorium, with 1821 actinide structures added to the Cambridge Structural Database since the beginning of 2006, a no. that accounts for 44% of the total actinide entries to date. Given this swelling vol. of research, there is a clear need for review articles to assist in providing a concise location for tracking progress in the different areas of actinide chem. The authors focus on the topic of nonaq. actinide coordination chem.
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      Cowie, B. E.; Purkis, J. M.; Austin, J.; Love, J. B.; Arnold, P. L. Thermal and Photochemical Reduction and Functionalization Chemistry of the Uranyl Dication, [UVIO2]2+. Chem. Rev. 2019, 119 (18), 10595– 10637,  DOI: 10.1021/acs.chemrev.9b00048
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      Thermal and Photochemical Reduction and Functionalization Chemistry of the Uranyl Dication, [UVIO2]2+
      Cowie, Bradley E.; Purkis, Jamie M.; Austin, Jonathan; Love, Jason B.; Arnold, Polly L.
      Chemical Reviews (Washington, DC, United States) (2019), 119 (18), 10595-10637CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. The uranyl ion, [UVIO2]2+, possesses rigorously trans, strongly covalent, and chem. robust U-oxo groups. However, through the use of anaerobic reaction techniques, both one and two-electron reductive functionalization of the uranyl oxo groups were discovered and developed. Prior to 2010, this unusual reactivity centered around the reductive silylation of the uranyl ion which entailed conversion of the oxo ligands into siloxy ligands, and reductive metalation of the uranyl oxo with Group 1 and f-block metals. This review surveys the large no. of new examples of reductive functionalization of the uranyl ion that are reported since 2010, including reductive borylation and alumination, metalation with d- or f-block metals, and new examples of reductive silylation. Other examples of oxo-group functionalization of [UVIO2]2+ that do not involve redn., mainly with Group 1 cations, are also covered, along with new advances in the photochem. of the uranyl(VI) ion that involve the transient formation of formally uranyl(V) [UVO2]+ ion.
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      A review. The uranyl dication, [UO2]2+, is the most prevalent and most thermodynamically stable form of uranium and is a sol. and problematic environmental contaminant. It is also extraordinarily chem. robust due to the strongly covalent trans-UO2 bonding. In contrast, the pentavalent uranyl cation [UO2]+ is unstable in an aq. environment with respect to disproportionation into tetravalent uranium species and [UO2]2+. Aside from fundamental interest, an understanding of the pentavalent [UO2]+ cation is desirable since it is important environmentally as a key intermediate in the pptn. of uranium from groundwater. In the last 2 years, the use of anaerobic coordination chem. techniques and organometallic reagents gave a few kinetically inert complexes contg. the f 1 [UO2]+ cation. The synthesis and characterization of these, and the insight they give into subsequent reactivity of the trans-UO2 unit, is discussed in this review.
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      Extending the Chemistry of the Uranyl Ion: Lewis Acid Coordination to a U:O Oxygen
      Sarsfield, Mark J.; Helliwell, Madeleine
      Journal of the American Chemical Society (2004), 126 (4), 1036-1037CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Treatment of the THF adduct UO2(NCN)THF (NCN = [(Me3SiN)CPh(NSiMe3)]) (1) with 2 equiv of B(C6F5)3 provides UO{OB(C6F5)3}(NCN)2 (2) the 1st example of a neutral uranyl complex exhibiting Lewis basic behavior. The crystal structure of 2 shows a U:O-B interaction with an elongated U:O bond (1.898(3) Å). Raman spectroscopy suggests weakening of the O:U:O bonding, giving the lowest reported sym. stretching frequency for a monomeric uranyl complex, ν1 = 780 cm-1. The borane can be selectively removed using PMe3 to give the coordinatively unsatd. UO2(NCN)2 (3) or using tBuNC to provide UO2(CNBut)(NCN)2 (4), the 1st example of an isonitrile coordinated to U.
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      Formation of Bare UO22+ and NUO+ by Fragmentation of Gas-Phase Uranyl-Acetonitrile Complexes
      Van Stipdonk, Michael J.; Michelini, Maria del Carmen; Plaviak, Alexandra; Martin, Dean; Gibson, John K.
      Journal of Physical Chemistry A (2014), 118 (36), 7838-7846CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      In a prior study [Van Stipdonk; et al. J. Phys. Chem. A 2006, 110, 959-970], electrospray ionization (ESI) was used to generate doubly charged complex ions composed of the uranyl ion and acetonitrile (acn) ligands. The complexes, general formula [UO2(acn)n]2+, n = 0-5, were isolated in an 3-D quadrupole ion-trap mass spectrometer to probe intrinsic reactions with H2O. Two general reaction pathways were obsd.: (a) the direct addn. of one or more H2O ligands to the doubly charged complexes and (b) charge-exchange reactions. For the former, the intrinsic tendency to add H2O was dependent on the no. and type of nitrile ligand. For the latter, charge exchange involved primarily the formation of uranyl hydroxide, [UO2OH]+, presumably via a collision with gas-phase H2O and the elimination of a protonated nitrile ligand. Examn. of general ion fragmentation patterns by collision-induced dissocn., however, was hindered by the pronounced tendency to generate hydrated species. In an update to this story, we have revisited the fragmentation of uranyl-acetonitrile complexes in a linear ion-trap (LIT) mass spectrometer. Lower partial pressures of adventitious H2O in the LIT (compared to the 3-D ion trap used in our previous study) minimized adduct formation and allowed access to lower uranyl coordination nos. than previously possible. We have now been able to investigate the fragmentation behavior of these complex ions completely, with a focus on tendency to undergo ligand elimination vs. charge redn. reactions. CID can be used to drive ligand elimination to completion to furnish the bare uranyl dication, UO22+. In addn., fragmentation of [UO2(acn)]2+ generated [UO2(NC)]+, which subsequently fragmented to furnish NUO+. Formation of the nitrido by transfer of N from cyanide was confirmed using precursors labeled with 15N. The obsd. formation of [UO2(NC)]+ and NUO+ was modeled by d. functional theory.
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      Gong, Y.; Vallet, V.; del Carmen Michelini, M.; Rios, D.; Gibson, J. K. Activation of Gas-Phase Uranyl: From an Oxo to a Nitrido Complex. J. Phys. Chem. A 2014, 118 (1), 325– 330,  DOI: 10.1021/jp4113798
      8
      Activation of Gas-Phase Uranyl: From an Oxo to a Nitrido Complex
      Gong, Yu; Vallet, Valerie; del Carmen Michelini, Maria; Rios, Daniel; Gibson, John K.
      Journal of Physical Chemistry A (2014), 118 (1), 325-330CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      The uranyl moiety, UO22+, is ubiquitous in the chem. of uranium, the most prevalent actinide. Replacing the strong uranium-oxygen bonds in uranyl with other ligands is very challenging, having met with only limited success. We report here uranyl oxo bond activation in the gas phase to form a terminal nitrido complex, a previously elusive transformation. Collision induced dissocn. of gas-phase UO2(NCO)-Cl2- in an ion trap produced the nitrido oxo complex, NUOCl2-, and CO2. NUOCl2- was computed by DFT to have Cs symmetry and a singlet ground state. The computed bond length and order indicate a triple U-N bond. Endothermic activation of UO2(NCO)-Cl2- to produce NUOCl2- and neutral CO2 was computed to be thermodynamically more favorable than NCO ligand loss. Complete reaction pathways for the CO2 elimination process were computed at the DFT level.
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    9. 9
      Gong, Y.; De Jong, W. A.; Gibson, J. K. Gas Phase Uranyl Activation: Formation of a Uranium Nitrosyl Complex from Uranyl Azide. J. Am. Chem. Soc. 2015, 137 (18), 5911– 5915,  DOI: 10.1021/jacs.5b02420
      9
      Gas Phase Uranyl Activation: Formation of a Uranium Nitrosyl Complex from Uranyl Azide
      Gong, Yu; de Jong, Wibe A.; Gibson, John K.
      Journal of the American Chemical Society (2015), 137 (18), 5911-5915CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Activation of the oxo bond of uranyl, UO22+, was achieved by collision induced dissocn. (CID) of UO2(N3)Cl2- in a quadrupole ion trap mass spectrometer. The gas phase complex UO2(N3)Cl2- was produced by electrospray ionization of solns. of UO2Cl2 and NaN3. CID of UO2(N3)Cl2- resulted in the loss of N2 to form UO(NO)Cl2-, in which the "inert" uranyl oxo bond has been activated. Formation of UO2Cl2- via N3 loss was also obsd. D. functional theory computations predict that the UO(NO)Cl2- complex has nonplanar Cs symmetry and a singlet ground state. Anal. of the bonding of the UO(NO)Cl2- complex shows that the side-on bonded NO moiety can be considered as NO3-, suggesting a formal oxidn. state of U(VI). Activation of the uranyl oxo bond in UO2(N3)Cl2- to form UO(NO)Cl2- and N2 was computed to be endothermic by 169 kJ/mol, which is energetically more favorable than formation of NUOCl2- and UO2Cl2-. The observation of UO2Cl2- during CID is most likely due to the absence of an energy barrier for neutral ligand loss.
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    10. 10
      Abergel, R. J.; de Jong, W. A.; Deblonde, G. J.-P.; Dau, P. D.; Captain, I.; Eaton, T. M.; Jian, J.; van Stipdonk, M. J.; Martens, J.; Berden, G.; Oomens, J.; Gibson, J. K. Cleaving off Uranyl Oxygens through Chelation: A Mechanistic Study in the Gas Phase. Inorg. Chem. 2017, 56 (21), 12930– 12937,  DOI: 10.1021/acs.inorgchem.7b01720
      10
      Cleaving Uranyl Oxygen through Chelation: Mechanistic Study in Gas Phase
      Abergel, Rebecca J.; de Jong, Wibe A.; Deblonde, Gauthier J.-P.; Dau, Phuong D.; Captain, Ilya; Eaton, Teresa M.; Jian, Jiwen; van Stipdonk, Michael J.; Martens, Jonathan; Berden, Giel; Oomens, Jos; Gibson, John K.
      Inorganic Chemistry (2017), 56 (21), 12930-12937CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      Recent efforts to activate the strong uranium-oxygen bonds in the dioxo uranyl cation have been limited to single oxo-group activation through either uranyl redn. and functionalization in soln., or by collision induced dissocn. (CID) in the gas-phase, using mass spectrometry (MS). Here, we report and investigate the surprising double activation of uranyl by an org. ligand, 3,4,3-LI(CAM), leading to the formation of a formal U6+ chelate in the gas-phase. The cleavage of both uranyl oxo bonds was exptl. evidenced by CID, using deuterium and 18O isotopic substitutions, and by IR multiple photon dissocn. (IRMPD) spectroscopy. D. functional theory (DFT) computations predict that the overall reaction requires only 132 kJ/mol, with the first oxygen activation entailing about 107 kJ/mol. Combined with anal. of similar, but unreactive ligands, these results shed light on the chelation-driven mechanism of uranyl oxo bond cleavage, demonstrating its dependence on the presence of ligand hydroxyl protons available for direct interactions with the uranyl oxygens.
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    11. 11
      Hu, S.-X.; Jian, J.; Li, J.; Gibson, J. K. Destruction of the Uranyl Moiety in a U(V) “Cation–Cation” Interaction. Inorg. Chem. 2019, 58 (15), 10148– 10159,  DOI: 10.1021/acs.inorgchem.9b01265
      11
      Destruction of the Uranyl Moiety in a U(V) "Cation-Cation" Interaction
      Hu, Shu-Xian; Jian, Jiwen; Li, Jun; Gibson, John K.
      Inorganic Chemistry (2019), 58 (15), 10148-10159CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      A gas-phase uranyl peroxide dimer supported by three 12-crown-4 ether (12C4) ligands, [(UO2)2(O2)(12C4)3]2+ (A), was prepd. by electrospray ionization. D. functional theory (DFT) indicates a structure with two terminal 12C4 and the third 12C4 bridging the uranium centers. Collision induced dissocn. (CID) of A resulted in elimination of the bridging 12C4 to yield a uranyl peroxide dimer with two terminal donor ligands, [(12C4)(UO2)(O2)(UO2)(12C4)]2+ (B). Remarkably, CID of B resulted in elimination of the bridging peroxide concomitant with redn. of U(VI) to U(V) in C, [(12C4)(UO2)(UO2)(12C4)]2+. DFT studies indicate that in C there is direct interaction between the two UO2+ species, which can thus be considered as a so-called cation-cation interaction (CCI). This formal CCI, induced by tetradentate 12C4 ligands, corresponds to destruction of the linear uranyl moieties and creation of bridging U-O-U oxo-bonds. On the basis of the structural rearrangement to achieve the structurally extreme CCI interaction, it is predicted also to be accessible for PaO2+ but is less feasible for transuranic actinyls.
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    12. 12
      Van Stipdonk, M. J.; Tatosian, I. J.; Iacovino, A. C.; Bubas, A. R.; Metzler, L. J.; Sherman, M. C.; Somogyi, A. Gas-Phase Deconstruction of UO22+: Mass Spectrometry Evidence for Generation of [OUVICH]+ by Collision-Induced Dissociation of [UVIO2 (C≡CH)]+. J. Am. Soc. Mass Spectrom. 2019, 30 (5), 796– 805,  DOI: 10.1007/s13361-019-02179-6
      12
      Gas-Phase Deconstruction of UO22+: Mass Spectrometry Evidence for Generation of [OUVICH]+ by Collision-Induced Dissociation of [UVIO2(C≃CH)]+
      van Stipdonk, Michael J.; Tatosian, Irena J.; Iacovino, Anna C.; Bubas, Amanda R.; Metzler, Luke J.; Sherman, Mary C.; Somogyi, Arpad
      Journal of the American Society for Mass Spectrometry (2019), 30 (5), 796-805CODEN: JAMSEF; ISSN:1044-0305. (Springer)
      Because of the high stability and inertness of the U:O bonds, activation and/or functionalization of UO22+ and UO2+ remain challenging tasks. We show here that collision-induced dissocn. (CID) of the uranyl-propiolate cation, [UVIO2(O2C-C≃CH)]+, can be used to prep. [UVIO2(C≃CH)]+ in the gas phase by decarboxylation. Remarkably, CID of [UVIO2(C≃CH)]+ caused elimination of CO to create [OUVICH]+, thus providing a new example of a well-defined substitution of an "yl" oxo ligand of UVIO22+ in a unimol. reaction. Relative energies for candidate structures based on d. functional theory calcns. suggest that the [OUVICH]+ ion is a uranium-methylidyne product, with a U≃C triple bond composed of one σ-bond with contributions from the U df and C sp. hybrid orbitals, and two π-bonds with contributions from the U df and C p orbitals. Upon isolation, without imposed collisional activation, [OUVICH]+ appears to react spontaneously with O2 to produce [UVO2]+.
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    13. 13
      Metzler, L. J.; Farmen, C. T.; Corcovilos, T. A.; Van Stipdonk, M. J. Intrinsic Chemistry of [OUCH]+: Reactions with H2O, CH3C≡N and O2. Phys. Chem. Chem. Phys. 2021, 23 (8), 4475– 4479,  DOI: 10.1039/D1CP00177A
      13
      Intrinsic chemistry of [OUCH]+: reactions with H2O, CH3CΞN and O2
      Metzler, Luke J.; Farmen, Christopher T.; Corcovilos, Theodore A.; Van Stipdonk, Michael J.
      Physical Chemistry Chemical Physics (2021), 23 (8), 4475-4479CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      We report the first exptl. study of the intrinsic chem. of a U-methylidyne species, focusing on reaction of [OUCH]+ with H2O, O2 and CH3CΞN in the gas phase. DFT was also used to det. reaction pathways, and establish the mechanism by which [OUCH]+ is formed through collision-induced dissocn. of [UO2(CΞCH)]+.
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    14. 14
      Van Stipdonk, M. J.; Perez, E. H.; Metzler, L. J.; Bubas, A. R.; Corcovilos, T.; Somogyi, A. Destruction and Reconstruction of UO22+ Using Gas-Phase Reactions. Phys. Chem. Chem. Phys. 2021, 23 (20), 11844– 11851,  DOI: 10.1039/D1CP01520F
      14
      Destruction and reconstruction of UO22+ using gas-phase reactions
      Van Stipdonk, Michael J.; Perez, Evan H.; Metzler, Luke J.; Bubas, Amanda R.; Corcovilos, Theodore; Somogyi, Arpad
      Physical Chemistry Chemical Physics (2021), 23 (20), 11844-11851CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      While the strong axial UO bonds confer high stability and inertness to UO22+, it has been shown that the axial oxo ligands can be eliminated or replaced in the gas-phase using collision-induced dissocn. (CID) reactions. We report here tandem mass spectrometry expts. initiated with a gas-phase complex that includes UO22+ coordinated by a 2,6-difluorobenzoate ligand. After decarboxylation to form a difluorophenide coordinated uranyl ion, [UO2(C6F2H3)]+, CID causes elimination of CO, and then CO and C2H2 in sequential dissocn. steps, to leave a reactive uranium fluoride ion, [UF2(C2H)]+. Reaction of [UF2(C2H)]+ with CH3OH creates [UF2(OCH3)]+, [UF(OCH3)2]+ and [UF(OCH3)2(CH3OH)]+. Cleavage of C-O bonds within these species results in the elimination of Me cation (CH3+). Subsequent CID steps convert [UF(OCH3)2]+ to [UO2(F)]+ and similarly, [U(OCH3)3]+ to [UO2(OCH3)]+. Our expts. show removal of both uranyl oxo ligands in "top-down" CID reactions and replacement in "bottom-up" ion-mol. and dissocn. steps.
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    15. 15
      Armentrout, P.; Beauchamp, J. Reactions of U+ and UO+ with O2, CO, CO2, COS, CS2 and D2O. Chem. Phys. 1980, 50 (1), 27– 36,  DOI: 10.1016/0301-0104(80)87022-4
      15
      Reactions of uranium(1+) and uranium monoxide(1+) ions with diatomic oxygen, carbon monoxide, carbon dioxide, carbon oxide sulfide, carbon disulfide and water-d2
      Armentrout, P. B.; Beauchamp, J. L.
      Chemical Physics (1980), 50 (1), 27-36CODEN: CMPHC2; ISSN:0301-0104.
      An ion-beam app. was used to study the reactions of U+ and UO+ with O2, CO, CO2, COS, CS2, and D2O. Reaction cross sections as functions of the ion kinetic energy were detd. and compared to simple models for exothermic and endothermic reactions. With 2 exceptions, all exothermic reactions exhibited large cross sections that decreased with increasing kinetic energy. The reactions of UO+ with CO2 and COS to form UO2+ exhibited substantial energy barriers; U+ reacted with CO to yield both UO+ and UC+ in endothermic processes. The thresholds for these reactions agree well with literature thermochem.
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    16. 16
      Jackson, G. P.; King, F. L.; Goeringer, D. E.; Duckworth, D. C. Gas-Phase Reactions of U+ and U2+ with O2 and H2O in a Quadrupole Ion Trap. J. Phys. Chem. A 2002, 106 (34), 7788– 7794,  DOI: 10.1021/jp0259420
      16
      Gas-Phase Reactions of U+ and U2+ with O2 and H2O in a Quadrupole Ion Trap
      Jackson, Glen P.; King, Fred L.; Goeringer, Douglas E.; Duckworth, Douglas C.
      Journal of Physical Chemistry A (2002), 106 (34), 7788-7794CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      Reaction pathways and rate consts. of gas-phase uranium and uranium oxide ions with O2 and H2O have been investigated using a quadrupole ion trap mass spectrometer (QIT-MS). A new reaction pathway is identified for the reaction between U2+ and H2O, which leads to the formation of UO+ via the intermediate UOH2+. Reaction rate consts. are detd. for several reactions by measuring the reaction rate at different partial pressures of the reagent gas and are found to be in reasonable agreement with the literature. These rate consts. include the first known measurement for the reaction of U2+ with H2O (∼0.4 kADO). New limits on thermochem. values are also provided for certain species. These include ΔHf (UO2+) ≤ 1742 kJ mol-1 and 1614 ≤ ΔHf (UOH2+) ≤ 1818 kJ mol-1 and are based on the assumption that only exothermic or thermoneutral reactions are possible under the conditions used. This assumption is supported by simulations of the root-mean-square (RMS) ion kinetic energy of stored uranium ions in the QIT. Only a slight increase in the RMS ion kinetic energies, from 0.1 to 0.2 eV, is predicted over the range of trapping conditions studied (0.05 ≤ qz ≤ 0.75) corresponding to a theor. reaction temp. of ∼384 K. The simulations also compare helium and neon as bath gases and show that the RMS kinetic energies are found to be very similar at long trapping times (>20 ms), although neon establishes steady state conditions in approx. half the time.
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    17. 17
      Zhang, W.-J.; Demireva, M.; Kim, J.; de Jong, W. A.; Armentrout, P. Reactions of U+ with H2, D2, and HD Studied by Guided Ion Beam Tandem Mass Spectrometry and Theory. J. Phys. Chem. A 2021, 125 (36), 7825– 7839,  DOI: 10.1021/acs.jpca.1c05409
      17
      Reactions of U+ with H2, D2, and HD Studied by Guided Ion Beam Tandem Mass Spectrometry and Theory
      Zhang, Wen-Jing; Demireva, Maria; Kim, JungSoo; de Jong, Wibe A.; Armentrout, P. B.
      Journal of Physical Chemistry A (2021), 125 (36), 7825-7839CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      The kinetic energy-dependent reactions of the at. actinide uranium cation (U+) with H2, D2, and HD were examd. by guided ion beam tandem mass spectrometry. An av. 0 K bond dissocn. energy of D0(U+ - H) = 2.48 ± 0.06 eV is obtained by anal. of the endothermic product ion cross sections. Quantum chem. calcns. were performed for comparison with exptl. thermochem., including high-level CASSCF-CASPT2-RASSI calcns. of the spin-orbit corrections. CCSD(T) and the CASSCF levels show excellent agreement with expt., whereas B3LYP and PBE0 slightly overestimate and the M06 approach badly underestimates the bond energy for UH+. Theory was also used to investigate the electronic structures of the reaction intermediates and potential energy surfaces. The exptl. product branching ratio for the reaction of U+ with HD indicates that these reactions occur primarily via a direct reaction mechanism, despite the presence of a deep-well for UH2+ formation according to theory. The reactivity and hydride bond energy for U+ are compared with those for transition metal, lanthanide, and actinide cations, and periodic trends are discussed. These comparisons suggest that the 5f electrons on uranium are largely core and uninvolved in the reactive chem.
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    18. 18
      Schröder, D.; Shaik, S.; Schwarz, H. Two-State Reactivity as a New Concept in Organometallic Chemistry. Acc. Chem. Res. 2000, 33 (3), 139– 145,  DOI: 10.1021/ar990028j
      18
      Two-state reactivity as a new concept in organometallic chemistry
      Schroder D; Shaik S; Schwarz H
      Accounts of chemical research (2000), 33 (3), 139-45 ISSN:0001-4842.
      It is proposed that spin-crossing effects can dramatically affect reaction mechanisms, rate constants, branching ratios, and temperature behaviors of organometallic transformations. This phenomenon is termed two-state reactivity (TSR) and involves participation of spin inversion in the rate-determining step. While the present analysis is based on studies of transition metals under idealized conditions, several recent reports imply that TSR is by no means confined to the gas phase. In fact, participation of more than a single spin surface in the reaction pathways is proposed as a key feature in organometallic chemistry.
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    19. 19
      Armentrout, P. B. Chemistry of Excited Electronic States. Science 1991, 251 (4990), 175– 179,  DOI: 10.1126/science.251.4990.175
      19
      Chemistry of excited electronic states
      Armentrout, P. B.
      Science (Washington, DC, United States) (1991), 251 (4990), 175-9CODEN: SCIEAS; ISSN:0036-8075.
      A review with 34 refs on at. and MO applications in chem.
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    20. 20
      Kaltsoyannis, N. Transuranic Computational Chemistry. Chem.─Eur. J. 2018, 24 (12), 2815– 2825,  DOI: 10.1002/chem.201704445
      20
      Transuranic Computational Chemistry
      Kaltsoyannis, Nikolas
      Chemistry - A European Journal (2018), 24 (12), 2815-2825CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. Recent developments in the chem. of the transuranic elements are surveyed, with particular emphasis on computational contributions. Examples are drawn from mol. coordination and organometallic chem., and from the study of extended solid systems. The role of the metal valence orbitals in covalent bonding is a particular focus, esp. the consequences of the stabilization of the 5f orbitals as the actinide series is traversed. The fledgling chem. of transuranic elements in the +II oxidn. state is highlighted. Throughout, the symbiotic interplay of exptl. and computational studies is emphasized; the extraordinary challenges of exptl. transuranic chem. afford computational chem. a particularly valuable role at the frontier of the periodic table.
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    21. 21
      Pegg, J. T.; Shields, A. E.; Storr, M. T.; Scanlon, D. O.; de Leeuw, N. H. Noncollinear Relativistic DFT + U Calculations of Actinide Dioxide Surfaces. J. Phys. Chem. C 2019, 123 (1), 356– 366,  DOI: 10.1021/acs.jpcc.8b07823
      21
      Noncollinear Relativistic DFT + U Calculations of Actinide Dioxide Surfaces
      Pegg, James T.; Shields, Ashley E.; Storr, Mark T.; Scanlon, David O.; de Leeuw, Nora H.
      Journal of Physical Chemistry C (2019), 123 (1), 356-366CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      A noncollinear relativistic PBEsol + U study of low-index actinide dioxides (AnO2, An = U, Np, or Pu) surfaces has been conducted. The importance of magnetic vector reorientation relative to the plane of the surface is highlighted; this has often been ignored in collinear nonrelativistic models. The use of noncollinear relativistic methods is key to the design of reliable computational models. The ionic relaxation of each surface is shown to be confined to the first three monolayers, and we have explored the configurations of the terminal oxygen ions on the reconstructed (001) surface. The reconstructed (001) surfaces are ordered as (001)αβ < (001)α < (001)β in terms of energetics. Electrostatic potential isosurface and scanning tunneling microscopy images have also been calcd. By considering the energetics of the low-index AnO2 surfaces, an octahedral Wulff crystal morphol. has been calcd.
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    22. 22
      Wdowik, U. D.; Piekarz, P.; Legut, D.; Jagło, G. Effect of Spin-Orbit and on-Site Coulomb Interactions on the Electronic Structure and Lattice Dynamics of Uranium Monocarbide. Phys. Rev. B 2016, 94 (5), 054303,  DOI: 10.1103/PhysRevB.94.054303
      22
      Effect of spin-orbit and on-site Coulomb interactions on the electronic structure and lattice dynamics of uranium monocarbide
      Wdowik, U. D.; Piekarz, P.; Legu, D.; Jaglo, G.
      Physical Review B (2016), 94 (5), 054303/1-054303/9CODEN: PRBHB7; ISSN:2469-9950. (American Physical Society)
      Uranium monocarbide, a potential fuel material for the generation IV reactors, is investigated within d. functional theory. Its electronic, magnetic, elastic, and phonon properties are analyzed and discussed in terms of spin-orbit interaction and localized vs. itinerant behavior of the 5f electrons. The localization of the 5f states is tuned by varying the local Coulomb repulsion interaction parameter. We demonstrate that the theor. electronic structure, elastic consts., phonon dispersions, and their densities of states can reproduce accurately the results of x-ray photoemission and bremsstrahlung isochromat measurements as well as inelastic neutron scattering expts. only when the 5f states experience the spin-orbit interaction and simultaneously remain partially localized. The partial localization of the 5f electrons could be represented by a moderate value of the on-site Coulomb interaction parameter of about 2 eV. The results of the present studies indicate that both strong electron correlations and spin-orbit effects are crucial for realistic theor. description of the ground-state properties of uranium carbide.
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    23. 23
      Marian, C. M. Spin–Orbit Coupling and Intersystem Crossing in Molecules. WIREs Comput. Mol. Sci. 2012, 2 (2), 187– 203,  DOI: 10.1002/wcms.83
      There is no corresponding record for this reference.
    24. 24
      Pereira, C. C. L.; Michelini, M. d. C.; Marcalo, J.; Gong, Y.; Gibson, J. K. Synthesis and Properties of Uranium Sulfide Cations. An Evaluation of the Stability of Thiouranyl, {S = U=S}2+. Inorg. Chem. 2013, 52 (24), 14162– 14167,  DOI: 10.1021/ic4020493
      24
      Synthesis and Properties of Uranium Sulfide Cations. An Evaluation of the Stability of Thiouranyl, {S=U=S}2+
      Pereira, Claudia C. L.; Michelini, Maria del Carmen; Marcalo, Joaquim; Gong, Yu; Gibson, John K.
      Inorganic Chemistry (2013), 52 (24), 14162-14167CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      Atomic uranium cations, U+ and U2+, reacted with the facile sulfur-atom donor OCS to produce several monopos. and dipos. uranium sulfide species contg. up to four sulfur atoms. Sequential abstraction of two sulfur atoms by U2+ resulted in US22+; d. functional theory computations indicate that the ground-state structure for this species is side-on η2-S2 triangular US22+, with the linear thiouranyl isomer, {S=UVI=S}2+, some 171 kJ mol-1 higher in energy. The result that the linear thiouranyl structure is a local min. at a moderate energy suggests that it should be feasible to stabilize this moiety in mol. compds.
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    25. 25
      Marks, J.; Rittgers, B.; Van Stipdonk, M.; Duncan, M. Photodissociation and Infrared Spectroscopy of Uranium–Nitrogen Cation Complexes. J. Phys. Chem. A 2021, 125 (33), 7278– 7288,  DOI: 10.1021/acs.jpca.1c05823
      25
      Photodissociation and Infrared Spectroscopy of Uranium-Nitrogen Cation Complexes
      Marks, J. H.; Rittgers, B. M.; Van Stipdonk, M. J.; Duncan, M. A.
      Journal of Physical Chemistry A (2021), 125 (33), 7278-7288CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      Laser vaporization of uranium in a pulsed supersonic expansion of nitrogen is used to produce complexes of the form U+(N2)n (n = 1-8). These ions are mass selected in a reflectron time-of-flight spectrometer and studied with visible and UV laser fixed-frequency photodissocn. and with tunable IR laser photodissocn. spectroscopy. The dissocn. patterns and spectroscopy of U+(N2)n indicate that N2 ligands are intact mols. and that there is no insertion chem. resulting in UN+ or NUN+. Fixed frequency photodissocn. at 532 and 355 nm indicate that the U+-N2 bond dissocn. energy varies little with changing coordination. The photon energy and the no. of ligands eliminated allow an est. of the av. U+-N2 dissocn. energy of 12 kcal/mol. IR bands are obsd. for these complexes near the N-N stretch vibration via elimination of N2 mols. These resonances are obsd. to be shifted about 130 cm-1 to the red from the free-N2 frequency for complexes with n = 3-8. D. functional theory indicates that U+ is most stable in the sextet state in these complexes and that N2 mols. bind in end-on configurations. The fully coordinated complex is predicted to be U+(N2)8, which has a cubic structure. The vibrational frequencies predicted by theory are consistently lower than those in the expt., independent of the isomeric structure or spin state of the complexes. Despite its failure to reproduce the IR spectra, theory provides an av. U+-N2 dissocn. energy of 11.8 ± 0.5 kcal/mol, in good agreement with the value from the expts.
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    26. 26
      Moreland, P. E., Jr; Rokop, D. J.; Stevens, C. M. Mass-Spectrometric Observations of Uranium and Plutonium Monohydrides Formed by Ion─Molecule Reaction. Int. J. Mass Spectrom. Ion Phys. 1970, 5 (1–2), 127– 136,  DOI: 10.1016/0020-7381(70)87011-5
      26
      Mass-spectrometric observations of uranium and plutonium monohydrides formed by ion-molecule reactions
      Moreland, Parker E.; Rokop, Donald J.; Stevens, Charles M.
      International Journal of Mass Spectrometry and Ion Physics (1970), 5 (1-2), 127-36CODEN: IJMIBY; ISSN:0020-7381.
      The monohydride ions UH+, UD+, PuH+, and PuD+ were obsd. in the mass spectrum of U and Pu during the isotopic anal. of these metals by surface ionization mass spectrometry. By introducing H and vapors of H compds. into the ion source, the hydrides could be produced by endothermic ion-mol. reactions of the metal-ion beam and residual gases. Hydride product ions were obtained with measurable intensity for the systems: U+ + H2, U+ + D2, U+ + H2O, U+ + D2O, U+ + H2S, Pu+ + H2, Pu+ + D2. Anal. of relatively crude product-ion energy spectra permits the dissociation energy D0(U+ - H) to be estd. at 3.3 ± 0.5 eV. The use of a retarding potential as a high-pass energy filter permits complete rejection of hydride ions in the mass spectrometer, due to the endothermic nature of the reactions involved.
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    27. 27
      Marçalo, J.; Santos, M.; Gibson, J. K. Gas-Phase Reactions of Doubly Charged Actinide Cations with Alkanes and Alkenes─Probing the Chemical Activity of 5f Electrons from Th to Cm. Phys. Chem. Chem. Phys. 2011, 13 (41), 18322– 18329,  DOI: 10.1039/c1cp21399g
      27
      Gas-phase reactions of doubly charged actinide cations with alkanes and alkenes-probing the chemical activity of 5f electrons from Th to Cm
      Marcalo, Joaquim; Santos, Marta; Gibson, John K.
      Physical Chemistry Chemical Physics (2011), 13 (41), 18322-18329CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      Small alkanes (methane, ethane, propane, n-butane) and alkenes (ethene, propene, 1-butene) were used to probe the gas-phase reactivity of doubly charged actinide cations, An2+ (An = Th, Pa, U, Np, Pu, Am, Cm), by means of Fourier transform ion cyclotron resonance mass spectrometry. Different combinations of doubly and singly charged ions were obsd. as reaction products, comprising species formed via metal-ion induced eliminations of small mols., simple adducts and ions resulting from electron, hydride or methide transfer channels. Th2+, Pa2+, U2+ and Np2+ preferentially yielded doubly charged products of hydrocarbon activation, while Pu2+, Am2+ and Cm2+ reacted mainly through transfer channels. Cm2+ was also capable of forming doubly charged products with some of the hydrocarbons whereas Pu2+ and Am2+ were not, these latter two ions conversely being the only for which adduct formation was obsd. The product distributions and the reaction efficiencies are discussed in relation to the electronic configurations of the metal ions, the energetics of the reactions and similar studies previously performed with doubly charged lanthanide and transition metal cations. The conditions for hydrocarbon activation to occur as related to the accessibility of electronic configurations with one or two 5f and/or 6d unpaired electrons are examd. and the possible chem. activity of the 5f electrons in these early actinide ions, particularly Pa2+, is considered.
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    28. 28
      Ephritikhine, M. Synthesis, Structure, and Reactions of Hydride, Borohydride, and Aluminohydride Compounds of the f-Elements. Chem. Rev. 1997, 97 (6), 2193– 2242,  DOI: 10.1021/cr960366n
      28
      Synthesis, Structure, and Reactions of Hydride, Borohydride, and Aluminohydride Compounds of the f-Elements
      Ephritikhine, Michel
      Chemical Reviews (Washington, D. C.) (1997), 97 (6), 2193-2242CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review with 304 refs. An assessment is given of the synthesis, structures, and reactions of mol. f-element hydrides. The hydrides of scandium, yttrium, and lanthanum are included because of their close similarity. Also presented are properties of the borohydride, aluminohydride, and alane compds. of these metals. Complexes with agostic C-H bonds are not discussed, nor are poly(pyrazolyl)borate complexes, which were the subject of another review (I. Santos, et al., 1995).
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    29. 29
      Totemeier, T. Characterization of Uranium Corrosion Products Involved in a Uranium Hydride Pyrophoric Event. J. Nucl. Mater. 2000, 278 (2–3), 301– 311,  DOI: 10.1016/S0022-3115(99)00245-7
      29
      Characterization of uranium corrosion products involved in a uranium hydride pyrophoric event
      Totemeier, T. C.
      Journal of Nuclear Materials (2000), 278 (2,3), 301-311CODEN: JNUMAM; ISSN:0022-3115. (Elsevier Science B.V.)
      Uranium metal corrosion products involved in a recent pyrophoric event were characterized using thermo-gravimetric anal., X-ray diffraction, and BET gas sorption techniques to det. the effects of passivation treatment and long-term storage on chem. reactivity. Characterization was performed on corrosion products in three different conditions: immediately after sepn. from the source metal, after low-temp. passivation, and after passivation and extended vault storage. The hydride fraction and ignition temp. of the corrosion products were found to be strongly dependent on the corrosion extent of the source metal. There was little change in corrosion product properties resulting from low-temp. passivation or vault storage. The results indicate that the energy source for the pyrophoric event was a considerable quantity of uranium hydride present in the corrosion products, but the specific ignition mechanism could not be identified.
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    30. 30
      Le Guyadec, F.; Génin, X.; Bayle, J.; Dugne, O.; Duhart-Barone, A.; Ablitzer, C. Pyrophoric Behaviour of Uranium Hydride and Uranium Powders. J. Nucl. Mater. 2010, 396 (2–3), 294– 302,  DOI: 10.1016/j.jnucmat.2009.11.007
      30
      Pyrophoric behaviour of uranium hydride and uranium powders
      Le Guyadec, F.; Genin, X.; Bayle, J. P.; Dugne, O.; Duhart-Barone, A.; Ablitzer, C.
      Journal of Nuclear Materials (2010), 396 (2-3), 294-302CODEN: JNUMAM; ISSN:0022-3115. (Elsevier B.V.)
      Thermal stability and spontaneous ignition conditions of uranium hydride and uranium metal fine powders have been studied and obsd. in an original and dedicated exptl. device placed inside a glove box under flowing pure argon. Pure uranium hydride powder with low amt. of oxide (<0.5 wt.%) was obtained by heat treatment at low temp. in flowing Ar/5%H2. Pure uranium powder was obtained by dehydration in flowing pure argon. Those fine powders showed spontaneous ignition at room temp. in air. An in situ CCD-camera displayed ignition assocd. with powder temp. measurement. Characterization of powders before and after ignition was performed by XRD measurements and SEM observations. Oxidn. mechanisms are proposed.
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  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jasms.3c00260.

    • Reaction energy diagram (PBE0 level of theory) for the generation of [UH]+ from [OUCH]+; proposed pathways for the reaction of [UH]+ and U+ with (neutral) O2 and H2O; experimental and computational methods; Cartesian coordinates for precursor, intermediate, and transition state structures; electronic energies and thermally corrected enthalpies for all species (PDF)


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