Search

The synthesis, reactivity, structures, and bonding in gas-phase binary and complex oxide anion molecules of protactinium and uranium have been studied by experiment and theory. The oxalate ions, AnVO2(C2O4)-, where An = Pa or U, are essentially actinyl ions, AnVO2+, coordinated by an oxalate dianion. Both react with water to yield the pentavalent hydroxides, AnVO(OH)2(C2O4)-. The chemistry of Pa and U becomes divergent for reactions that result in oxidation: whereas PaVI is inaccessible, UVI is very stable. The UVO2(C2O4)- complex exhibits a remarkable spontaneous exothermic replacement of the oxalate ligand by O2 to yield UO4- and two CO2 molecules. The structure of the uranium tetroxide anion is computed to correspond to distorted uranyl, UVIO22+, coordinated in the equatorial plane by two equivalent O atoms each having formal charges of -1.5 and U-O bond orders intermediate between single and double. The unreactive nature of PaVO2(C2O4)- toward O2 is a manifestation of the resistance toward oxidation of PaV, and clearly reveals the disparate chemistries of Pa and U. The uranium tetroxide anion, UO4-, reacts with water to yield UO5H2-. Infrared spectra obtained for UO5H2- confirm the computed lowest-energy structure, UO3(OH)2-.

Gas-phase organoactinyl complexes possessing discrete An-C bonds (An = U, Np, Pu) were synthesized in a quadrupole ion trap by endothermic decarboxylation of [AnO2(O2C-R)3]- anion complexes in which a formally AnO22+ actinyl core is coordinated by three carboxylate ligands, with R = CH3 (methyl), CH3CC (1-propynyl), C6H5 (phenyl), C6F5 (pentafluorophenyl). Decarboxylation and competing ligand loss were studied computationally by density functional theory complementing experiment. Although decarboxylation was computed to be the energetically most favorable process in all cases, reduction from An(VI) to An(V) via neutral ligand loss was often prevalent, particularly for An = Np, Pu, presumably resulting from barriers associated with decarboxylation. Comparative hydrolysis rates of the An-C bonds were experimentally determined, and the chemical properties of these bonds were analyzed by the quantum theory of atoms in molecules. The measured hydrolysis rates differed by up to 3 orders of magnitude: the fastest was for [(CH3CC)UO2(O2C-CCCH3)2]- and the slowest for [(C6F5)PuO2(O2C-C6F5)2]-. There is a general correlation between hydrolysis exothermicity and hydrolysis rate. Prototypical hydrolysis reaction pathways computed for R = CH3 (An = U, Np) reveal a mechanism in which an outer-sphere water becomes inner-sphere concomitant with transfer of an H atom to yield an OH ligand and CH4, with a net energy release of 170 kJ mol-1 and a transition state barrier of 45 kJ mol-1 for An = U. Infrared multiphoton dissociation spectra of selected complexes were acquired to confirm the predicted structures by agreement between the computed and observed vibrational frequencies. The experiment and theory results provide an evaluation of the comparative propensities for formation of the organoactinyls as a function of actinide and carboxylate and an assessment of the nature and stability toward hydrolysis of the primarily ionic An-C bonds.

Difficulty in the preparation of gas-phase ions that include U in middle oxidation states(III , IV) have hampered efforts to investigate intrinsic structure, bonding and reactivity of model species. Our group has used preparative tandem mass spectrometry (PTMS) to synthesize a gas-phase U-methylidyne species, [O＝U≡CH]+, by elimination of CO from [UO2(C≡CH)]+ [M. J. van Stipdonk, I. J. Tatosian, A. C. Iacovino, A. R. Bubas, L. Metzler, M. C. Sherman and A. Somogyi, J. Am. Soc. Mass Spectrom., 2019, 30, 796–805], which has been used as an intermediate to create products such as [OUN]+ and [OUS]+ by ion-molecule reactions. Here, we investigated the reactions of [O＝U≡CH]+ with a range of alkyl halides to determine whether the methylidyne is a also a useful intermediate for production and study of the oxy-halide ions [OUX]+, where X = Cl, Br and I, formally U(IV) species for which intrinsic reactivity data is relatively scarce. Our experiments demonstrate that [OUX]+ is the dominant product ion generated by reaction [O＝U≡CH]+ with neutral regents such as CH3Cl, CH3CH2Br and CH2＝CHCH2I. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Rationale: Building on our report that collision-induced dissociation (CID) can be used to create the highly reactive U-alkylidyne species [O=U≡CH]+, our goal was to determine whether the species could be as an intermediate for synthesis of [OUS]+ by reaction with carbon disulfide (CS2). Methods: Cationic uranyl-propiolate precursor ions were generated by electrospray ionization, and multiple-stage CID in a linear trap instrument was used to prepare [O=U≡CH]+. Neutral CS2 was admitted into the trap through a modified He inlet and precision leak valves. Results: The [O=U≡CH]+ ion reacts with CS2 to generate [OUS]+. CID of [OUS]+ causes elimination of the axial sulfide ligand to generate [OU]+. Using isotopically labeled reagent, we found that [OUS]+ reacts with O2 to create [UO2]+. Conclusions: [O=U≡CH]+ proves to be a useful reagent ion for synthesis of [OUS]+, a species that to date has only been created by gas-phase reactions of U+ and U2+. Dissociation of [OUS]+ to create [OU]+, but not [US]+, and the efficient conversion of the species into [UO2]+, is consistent with the relative differences in U-O and U-S bond energies. [ABSTRACT FROM AUTHOR]

While the strong axial U＝O 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 dissociation (CID) reactions. We report here tandem mass spectrometry experiments 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 dissociation 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 methyl cation (CH3+). Subsequent CID steps convert [UF(OCH3)2]+ to [UO2(F)]+ and similarly, [U(OCH3)3]+ to [UO2(OCH3)]+. Our experiments show removal of both uranyl oxo ligands in "top-down" CID reactions and replacement in "bottom-up" ion–molecule and dissociation steps. [ABSTRACT FROM AUTHOR]

We report the first experimental study of the intrinsic chemistry of a U-methylidyne species, focusing on reaction of [OUCH]+ with H2O, O2 and CH3C≡N in the gas phase. DFT was also used to determine reaction pathways, and establish the mechanism by which [OUCH]+ is formed through collision-induced dissociation of [UO2(C≡CH)]+. [ABSTRACT FROM AUTHOR]

Rationale The lower levels of adventitious H2O in a linear ion trap allow the fragmentation reactions of [UO2OCH3]+ and [UO2OCH2CH3]+ to be examined in detail. Methods Methanol- and ethanol-coordinated UO22+-alkoxide precursors were generated by electrospray ionization (ESI). Multiple-stage tandem mass spectrometry (MSn) and collision-induced dissociation (CID) were performed using a linear ion trap mass spectrometer. Results CID of [UO2OCH3(CH3OH)n]+ and [UO2OCH2CH3(CH3CH2OH)n]+, n = 3 and 2, causes loss of neutral alcohol ligands, leading ultimately to bare uranyl-alkoxide species. Comparison of 'native' to deuterium-labeled precursors reveals dissociation pathways not previously observed in 3-D ion trap experiments. Conclusions UO2H+ is generated from [UO2OCH3]+ by transfer of H from the methyl group. Variable-energy and variable-time CID experiments suggest that the apparent threshold for production of UO2H+ is lower than for UO2+, but the pathway is kinetically less favored for the former than for the latter. CID experiments reveal that [UO2OCH2CH3]+ dissociates to generate [UO2CH3]+, a relatively rare species with a U-C bond, and [UO2(O = CH2)]+. [ABSTRACT FROM AUTHOR]

We demonstrate 3D microwave projection sideband cooling of trapped, neutral atoms. The technique employs state-dependent potentials that enable microwave photons to drive vibration-number reducing transitions. The particular cooling sequence we employ uses minimal spontaneous emission, and works even for relatively weakly bound atoms. We cool 76% of atoms to their 3D vibrational ground states in a site-resolvable 3D optical lattice. [ABSTRACT FROM AUTHOR]

We demonstrate arbitrary coherent addressing of individual neutral atoms in a 5×5×5 array formed by an optical lattice. Addressing is accomplished using rapidly reconfigurable crossed laser beams to selectively ac Stark shift target atoms, so that only target atoms are resonant with state-changing microwaves. The effect of these targeted single qubit gates on the quantum information stored in non-targeted atoms is smaller than 3×10-3 in state fidelity. This is an important step along the path of converting the scalability promise of neutral atoms into reality. [ABSTRACT FROM AUTHOR]

Rationale: Building on our report that collision-induced dissociation (CID) can be used to create the highly reactive U-alkylidyne species [O=U≡CH]+, our goal was to determine whether the species could be as an intermediate for synthesis of [OUS]+ by reaction with carbon disulfide (CS2). Methods: Cationic uranyl-propiolate precursor ions were generated by electrospray ionization, and multiple-stage CID in a linear trap instrument was used to prepare [O=U≡CH]+. Neutral CS2 was admitted into the trap through a modified He inlet and precision leak valves. Results: The [O=U≡CH]+ ion reacts with CS2 to generate [OUS]+. CID of [OUS]+ causes elimination of the axial sulfide ligand to generate [OU]+. Using isotopically labeled reagent, we found that [OUS]+ reacts with O2 to create [UO2]+. Conclusions: [O=U≡CH]+ proves to be a useful reagent ion for synthesis of [OUS]+, a species that to date has only been created by gas-phase reactions of U+ and U2+. Dissociation of [OUS]+ to create [OU]+, but not [US]+, and the efficient conversion of the species into [UO2]+, is consistent with the relative differences in U-O and U-S bond energies. [ABSTRACT FROM AUTHOR]

One challenge in the quest to map the intrinsic reactivity of model actinide species has been the controlled synthesis of organo-actinide ions in the gas phase. We report here evidence that a series of gas-phase, σ-bonded [U-R] + species (where R = CH 3 , C 2 H 3 , C 2 H 5 , C 3 H 7 , or C 5 H 6 ) can be generated for subsequent study of ion-molecule chemistry by using preparative tandem mass spectrometry (PTMS n ) via ion-molecule reactions between [UH] + and a series of nitriles. Density functional theory calculations support the hypothesis that the [U-R] + ions are created in a pathway that involves intramolecular hydride attack and the elimination of neutral HCN. Subsequent reactivity experiments revealed that the [UCH 3 ] + readily undergoes hydrolysis, yielding cationic uranium hydroxide ([UOH] + ) and methane (CH 4 ). Other possible reaction pathways, such as the spontaneous rearrangement to [HUCH 2 ] + , are shown by theoretical calculations to have energy barriers, strengthening the evidence for the formation of a σ-bonded [U-CH 3 ] + complex in the gas-phase.

Difficulty in the preparation of gas-phase ions that include U in middle oxidation states(III,IV) have hampered efforts to investigate intrinsic structure, bonding and reactivity of model species. Our group has used preparative tandem mass spectrometry (PTMS) to synthesize a gas-phase U-methylidyne species, [OUCH] + , by elimination of CO from [UO 2 (CCH)] + [M. J. van Stipdonk, I. J. Tatosian, A. C. Iacovino, A. R. Bubas, L. Metzler, M. C. Sherman and A. Somogyi, J. Am. Soc. Mass Spectrom. , 2019, 30 , 796-805], which has been used as an intermediate to create products such as [OUN] + and [OUS] + by ion-molecule reactions. Here, we investigated the reactions of [OUCH] + with a range of alkyl halides to determine whether the methylidyne is a also a useful intermediate for production and study of the oxy-halide ions [OUX] + , where X = Cl, Br and I, formally U(IV) species for which intrinsic reactivity data is relatively scarce. Our experiments demonstrate that [OUX] + is the dominant product ion generated by reaction [OUCH] + with neutral regents such as CH 3 Cl, CH 3 CH 2 Br and CH 2 CHCH 2 I.

Multiple-stage collision-induced dissociation (CID) of a uranyl propiolate cation, [UO 2 (O 2 C-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] + , followed by a loss of H + , followed by a loss of H • . A feasible, multiple-step pathway for the generation of [UH] + . 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 + directly from a UO + directly from a UO 2 2+ precursor for the subsequent investigation of ion-molecule reactivity.

Rationale: Building on our report that collision-induced dissociation (CID) can be used to create the highly reactive U-alkylidyne species [O=U≡CH] + , our goal was to determine whether the species could be as an intermediate for synthesis of [OUS] + by reaction with carbon disulfide (CS 2 )., Methods: Cationic uranyl-propiolate precursor ions were generated by electrospray ionization, and multiple-stage CID in a linear trap instrument was used to prepare [O=U≡CH] + . Neutral CS 2 was admitted into the trap through a modified He inlet and precision leak valves., Results: The [O=U≡CH] + ion reacts with CS 2 to generate [OUS] + . CID of [OUS] + causes elimination of the axial sulfide ligand to generate [OU] + . Using isotopically labeled reagent, we found that [OUS] + reacts with O 2 to create [UO 2 ] + ., Conclusions: [O=U≡CH] + proves to be a useful reagent ion for synthesis of [OUS] + , a species that to date has only been created by gas-phase reactions of U + and U 2+ . Dissociation of [OUS] + to create [OU] + , but not [US] + , and the efficient conversion of the species into [UO 2 ] + , is consistent with the relative differences in U-O and U-S bond energies., (© 2022 John Wiley & Sons Ltd.)

We report the first experimental study of the intrinsic chemistry of a U-methylidyne species, focusing on reaction of [OUCH]+ with H2O, O2 and CH3C[triple bond, length as m-dash]N in the gas phase. DFT was also used to determine reaction pathways, and establish the mechanism by which [OUCH]+ is formed through collision-induced dissociation of [UO2(C[triple bond, length as m-dash]CH)]+.

Electrospray ionization was used to generate species such as [ZnNO 3 (CH 3 OH) 2 ] + from Zn(NO 3 ) 2 •XH 2 O dissolved in a mixture of CH 3 OH and H 2 O. Collision-induced dissociation of [ZnNO 3 (CH 3 OH) 2 ] + causes elimination of CH 3 OH to form [ZnNO 3 (CH 3 OH)] + . Subsequent collision-induced dissociation of [ZnNO 3 (CH 3 OH)] + causes elimination of 47 mass units (u), consistent with ejection of HNO 2 . The neutral loss shifts to 48 u for collision-induced dissociation of [ZnNO 3 (CD 3 OH)] + , demonstrating the ejection of HNO 2 involves intra-complex transfer of H from the methyl group methanol ligand. Subsequent collision-induced dissociation causes the elimination of 30 u (32 u for the complex with CD 3 OH), suggesting the elimination of formaldehyde (CH 2  = O). The product ion is [ZnOH] + . Collision-induced dissociation of a precursor complex created using CH 3 - 18 OH shows the isotope label is retained in CH 2  = O. Density functional theory calculations suggested that the "rearranged" product, ZnOH with bound HNO 2 and formaldehyde is significantly lower in energy than ZnNO 3 with bound methanol. We therefore used infrared multiple-photon photodissociation spectroscopy to determine the structures of both [ZnNO 3 (CH 3 OH) 2 ] + and [ZnNO 3 (CH 3 OH)] + . The infrared spectra clearly show that both ions contain intact nitrate and methanol ligands, which suggests that rearrangement occurs during collision-induced dissociation of [ZnNO 3 (CH 3 OH)] + . Based on the density functional theory calculations, we propose that transfer of H, from the methyl group of the CH 3 OH ligand to nitrate, occurs in concert with the formation of a Zn-C bond. After dissociation to release HNO 2 , the product rearranges with the insertion of the remaining O atom into the Zn-C bond. Subsequent C-O bond cleavage, with H transfer, produces an ion-molecule complex composed of [ZnOH] + and O = CH 2 .

Rationale: The lower levels of adventitious H2 O in a linear ion trap allow the fragmentation reactions of [UO2 OCH3 ](+) and [UO2 OCH2 CH3 ](+) to be examined in detail., Methods: Methanol- and ethanol-coordinated UO2 (2+) -alkoxide precursors were generated by electrospray ionization (ESI). Multiple-stage tandem mass spectrometry (MS(n) ) and collision-induced dissociation (CID) were performed using a linear ion trap mass spectrometer., Results: CID of [UO2 OCH3 (CH3 OH)n ](+) and [UO2 OCH2 CH3 (CH3 CH2 OH)n ](+) , n = 3 and 2, causes loss of neutral alcohol ligands, leading ultimately to bare uranyl-alkoxide species. Comparison of 'native' to deuterium-labeled precursors reveals dissociation pathways not previously observed in 3-D ion trap experiments., Conclusions: UO2 H(+) is generated from [UO2 OCH3 ](+) by transfer of H from the methyl group. Variable-energy and variable-time CID experiments suggest that the apparent threshold for production of UO2 H(+) is lower than for UO2 (+) , but the pathway is kinetically less favored for the former than for the latter. CID experiments reveal that [UO2 OCH2 CH3 ](+) dissociates to generate [UO2 CH3 ](+) , a relatively rare species with a U-C bond, and [UO2 (O = CH2 )](+) ., (Copyright © 2016 John Wiley & Sons, Ltd.)