- FTMS studies of sputtered metal cluster ions. (II) The chemistry of Nin+ with C2H4 and CH4 at long timescales
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Nickel cluster cations, generated in an external source by sputtering with 20 keV Xe+ were transferred to the ICR cell of a Fourier transform mass spectrometer (FTMS), collisionally cooled, and trapped for long time periods. During storage, the chemistry of Nin+ was studied with ethylene and methane in the range n = 1 ... 20. Rather than undergoing adsorption as an intact unit, C2H4 was dehydrogenated in the 1.2-position to yield HCCH adducts Nin(C2H2)m+ with a dramatic size-specificity: Whereas Nin+ ions proved absolutely inert for n = 1, 3, 4, they were found highly reactive from n = 5 on. Cyclotroning in the presence of C2H4 for up to 40 s, Ni5+ was found to add on a maximum of nine C2H2 ligands. A second 'hidden' size-specific effect was discovered between n = 11 and n = 12, where dehydrogenation intensifies to yield NinC6+ as final products. These are being discussed in terms of close-packed lattice structures. Finally, the threshold for methane activation by Ni5+ leading to Ni5C+ was determined to be 2.0 ± 0.5 eV.
- Irion,Selinger
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- Guided Ion Beam Studies of the Reactions of Co+ and Ni+ with CH3X (X = Cl, Br, I). Implications for the Metal-Methyl Ion Bond Energies
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Guided ion beam techniques are used to studie the reactions of Co+ and Ni+ with the methyl halides.The only products observed in these reactions are MCH3+ and MX+.Bond energies for the MCH3+ species a
- Fisher, Ellen R.,Sunderlin, L. S.,Armentrout, P. B.
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- Ni+(H2)n: Ligand bond energies for ground state ions
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The H2 ligand binding energies in Ni+(H2)n were measured to be 17.3, 17.6, 11.3, 7.1 and 4.2 kcal/mol, for n=1-5, respectively. The very weakly bound sixth ligand begins a new solvation sphere. Association entropies were also measured. MP2 calculations were done to determine geometries and vibration frequencies as well as the origin of the bonding. The observed changes in BDE with ligation are due to electronic rather than steric effects. Comparisons are made to the Fe+(H2)n, Co+(H2)n, Cu+(H2)n and Ni+(CO)n systems. A highly symmetric D3h planar structure is found in Ni+(H2)3 and forms the core of the Ni+(H2)4, 5 ions.
- Kemper, Paul R.,Weis, Patrick,Bowers, Michael T.
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- Reactions of Co+, Ni+, and Cu+ with Cyclopropane and Ethylene Oxide. Metal-Methylidene Ion Bond Energies
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The reactions of atomic cobalt, nickel, and copper ions with cyclopropane and ethylene oxide have been studied by using guided ion beam mass spectrometry.A predominant process in all these systems is formation of MCH2+.Analyses of these endothermic reactions yield the bond energies D0 (Co+-CH2) = 77.5 +/- 2.3 kcal/mol, D0 (Ni+-CH2) = 75.2 +/- 1.8 kcal/mol, and D0 (Cu+-CH2) = 63.9 +/- 1.6 kcal/mol.Differences between these values and those derived from earlier studies for Co+ and Ni+ are discussed.In addition to D0 (M+-CH2), bond energies for Co+-H, M-H (M = Co, Ni, Cu) and M+-O and M-O (M = Co, Ni) are evaluated and lower limits are placed on D0 (M+-C2H4) and D0 (M+-C2H2) (M = Co, Ni, Cu).The reaction mechanism for these reactions is also discussed in detail.
- Fisher, Ellen R.,Armentrout, P. B.
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- Gas-phase chemistry of bare transition-metal ions in comparison
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Some basic principles of gas-phase organometallic chemistry are demonstrated, exemplified for the model compound 2-methylbutanenitrile (5). The reactions of first-row transition-metal ions with 5 and its deuterated isotopomers 5a-5c reveal a distinct infl
- Eller,Zummack,Schwarz
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p. 621 - 627
(2007/10/02)
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- Kinetic Energy Release Distributions as a Probe of Transition-Metal-Mediated H-H, C-H, and C-C Bond Formation Processes: Reactions of Cobalt and Nickel Ions with Alkanes
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Product translational energy release distributions are used to investigate the potential energy surfaces for elimination of H2 and small hydrocarbons from ionic cobalt and nickel complexes with alkanes.The amount of energy appearing as product translation can be used to infer details of the potential energy surfaces in the region of the exit channel and has implications for the ease with which the reverse reactions may occur.The potential energy surfaces for hydrogen and alkane elimination reactions are discussed in view of the very different kinetic energy release distributions observed for these processes.For dehydrogenation reactions, both the shape of the distribution and the maximum kinetic energy release are correlated with the reaction mechanism.For example, the amount of energy apearing in product translation is quite distinctive between reactions known to involve metal-induced 1,2- and 1,4-hydrogen elimination.The selective dehydrogenations of 2-methyl-propane-2-d1 by Co+ and butane-1,1,1,4,4,4-d6 by Ni+ serve, respectively, as models for these processes.A comparison of these translational energy distributions with those observed for loss of H2, HD, and D2 from the dehydrogenation of butan-1,1,1,4,4,4-d6 by Co+ suggest that 1,4-elimination is dominant for the cobalt system and that the observation of different isotopic products results from scrambling processes.All the dehydrogenation processes examined were characterized by kinetic energy release distributions which could not be described by statistical theories.For these reactions, the maximum kinetic energy release approaches the estimated reaction exothermicity.In contrast, the more exothermic alkane eliminations have maximum kinetic energy releases which are less than half the reaction exothermicity, and the distributions can be fit with statistical models.For these processes the excess energy in the activated complex is approximately equal to the reaction exothermicity, suggesting a loose transition state for the disruption of a complex in which the intact alkane to be eliminated is interacting strongly with the metal center.Comparison of experiment with theory yields a Co+-propene bond strength of 48 +/- 3 kcal/mol, a Co+-CO bond strength of 34 +/- 3 kcal/mol, and a sum of the first and second metal bond strengths in Co(CD3)2+ of 110 +/- 3 kcal/mol at 298 K.The latter two values are derived from statistical kinetic energy release distributions observed for the loss of C2D6 and CO, respectively, in the reaction of Co+ with aceton-d6.
- Hanratty, Maureen A.,Beauchamp, J. L.,Illies, Andreas J.,Koppen, Petra van,Bowers, M. T.
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- Charge separation (coulomb explosion) processes of doubly charged cations of sandwich compounds in the gas phase: evidence for the junction of two C5H5 units
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The charge separation reactions (coulomb explosion) of the ferrocene, cobaltocene, and nickelocene dications, generated by electron impact ionization in the gas phase, are reported.These sandwich dications display a common behaviour in their unimolecular decomposition reactions, which are characterized by two distinct charge separation pathways.One corresponds to the reaction 2+ + + C5H5+, and the other to the generation of and M+ (M=Fe, Co, Ni).From the translational energy releases, associated with the charge separation processes, the intercharge distances of the exploding dications in their transition structures have been calculated.The results demonstrate that, irrespective of the nature of the transition metal ion M, the interchange distance for the formation of +/C5H5+ is 5.0 angstroem and 6.2 angstroem for the generation of and M+.
- Drewello, Thomas,Lebrilla, Carlito B.,Schwarz, Helmut,Ast, Teodor
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p. 333 - 338
(2007/10/02)
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- Transition-Metal Cation Chemistry in 1 Torr of He: M+ + C2H6 Reaction Rates
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We have used laser vaporization of solid metal targets to create first transition series gas-phase metal cations M+ in a fast flow reactor with 1 Torr of He buffer gas.In contrast with single-collision results, all ten first transition series M+ ions, Sc+ through Zn+, react with C2H6 in our multicollision experiment.The major primary product is usually the adduct ion MC2H6+ arising from third-body collisional stabilization of long-lived intermediates.The primary reaction rates vary a factor of 250 across the series.M+ ions having ground-state or low-energy 3dn electron configurations react the fastest with alkanes in 1 Torr of He.
- Tonkyn, Russ,Weisshaar, James C.
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p. 2305 - 2308
(2007/10/02)
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- Colloidal Silver Catalyzed Multi-Electron Transfer Processes in Aqueous Solution
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(CH3)2COH radicals were γ-radiolytically produced in aqueous solutions of colloidal silver (2.5 * 10-4 mol/l, acetone (0.1-0.2 M) and propanol-2 (0.2-0.4 M).The radicals were able to reduce Cd2+, N2O, and NO3- with yields of practically 100percent.In the absence of colloidal silver, Cd2+ was not reduced, but N2O or NO3- were reduced with yields of the order of 1percent.The reduction processes in the presence of silver occurred in competition with the reduction of water by the organic radicals.The catalytic action of colloidal silver is explained by electron transferfrom the organic radicals to the silver particles that become a pool of electrons and adsorbed hydrogen atoms.The stored electrons are then used to carry out the reduction of water or of dissolved substances.Relative rate constants for a number of multi-electron transfer processes at the colloidal silver pool are given and details of the reaction mechanism including the action of adsorbed Hδ- atoms are discussed. - Radiolytically produced Cd+ ions were also reduced at the colloidal silver pool.However, Zn+, Ni+, and Co+ were found to transfer an electron to the pool.The homogeneous reaction between NO3- and (CH3)2COH was also investigated.A rate constant of 28 M-1s-1 was found for this reaction.
- Henglein, A.
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p. 253 - 259
(2007/10/02)
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