Limbach, H. H. and Ulrich, S. and Grundemann, S. and Buntkowsky, G. and Sabo-Etienne, S. and Chaudret, B. and Kubas, G. J. and Eckert, J. (1998):
NMR and INS line shapes of transition metal hydrides in the presence of coherent and incoherent dihydrogen exchange.
In: Journal of the American Chemical Society, 120 (31), pp. 7929-7943. [Article]
Abstract
In this paper a unified description of the effects of the coherent and incoherent dihydrogen exchange on the NMR and INS spectra of transition metal hydrides based on the quantum-mechanical density matrix formalism of Alexander-Binsch is proposed. The dynamic parameters of the line shape analyses are the exchange couplings or rotational tunnel splittings J of the coherent exchange and the rate constants k of the incoherent exchange. As experimental examples, we report the temperature dependent values J and k for 1 equivalent to Cp*RuH3(PCy3) (Cp* equivalent to C-5(CH3)(5) and Cy equivalent to cyclohexyl) including the kinetic HH/HD/DD isotope effects on the incoherent exchange, determined by NMR, and for the tungsten dihydrogen complex 2 equivalent to W(PCy3)(2) (CO)(3)-(eta-H-2), determined by INS. The temperature dependence of J and Ic is interpreted qualitatively in terms of a simple reaction scheme involving at each temperature a ground state and a dominant ro-vibrationally excited state. Using formal kinetics it is shown that a coherent exchange in the excited state contributes to J only if this exchange presents the rate Limiting reaction step, i.e., if vibrational deactivation is fast. This is the case for levels located substantially below the top of the barrier. A very fast coherent exchange of levels located close to the top of the barrier contributes only to k. This result reproduces in a simple way the quantum-mechanical results of Szymanski, S. J. Chem. Phys. 1996, 104, 8216 and Scheurer, C.; Wiedenbruch, R.; Meyer, R.; Ernst, R. R. J. Chern. Phys. 1997, 106, 1. The results concerning the coherent and incoherent exchange processes in 1 and 2 are discussed in terms of the simplified reaction model.
| Item Type: | Article |
|---|---|
| Erschienen: | 1998 |
| Creators: | Limbach, H. H. and Ulrich, S. and Grundemann, S. and Buntkowsky, G. and Sabo-Etienne, S. and Chaudret, B. and Kubas, G. J. and Eckert, J. |
| Title: | NMR and INS line shapes of transition metal hydrides in the presence of coherent and incoherent dihydrogen exchange |
| Language: | English |
| Abstract: | In this paper a unified description of the effects of the coherent and incoherent dihydrogen exchange on the NMR and INS spectra of transition metal hydrides based on the quantum-mechanical density matrix formalism of Alexander-Binsch is proposed. The dynamic parameters of the line shape analyses are the exchange couplings or rotational tunnel splittings J of the coherent exchange and the rate constants k of the incoherent exchange. As experimental examples, we report the temperature dependent values J and k for 1 equivalent to Cp*RuH3(PCy3) (Cp* equivalent to C-5(CH3)(5) and Cy equivalent to cyclohexyl) including the kinetic HH/HD/DD isotope effects on the incoherent exchange, determined by NMR, and for the tungsten dihydrogen complex 2 equivalent to W(PCy3)(2) (CO)(3)-(eta-H-2), determined by INS. The temperature dependence of J and Ic is interpreted qualitatively in terms of a simple reaction scheme involving at each temperature a ground state and a dominant ro-vibrationally excited state. Using formal kinetics it is shown that a coherent exchange in the excited state contributes to J only if this exchange presents the rate Limiting reaction step, i.e., if vibrational deactivation is fast. This is the case for levels located substantially below the top of the barrier. A very fast coherent exchange of levels located close to the top of the barrier contributes only to k. This result reproduces in a simple way the quantum-mechanical results of Szymanski, S. J. Chem. Phys. 1996, 104, 8216 and Scheurer, C.; Wiedenbruch, R.; Meyer, R.; Ernst, R. R. J. Chern. Phys. 1997, 106, 1. The results concerning the coherent and incoherent exchange processes in 1 and 2 are discussed in terms of the simplified reaction model. |
| Journal or Publication Title: | Journal of the American Chemical Society |
| Journal volume: | 120 |
| Number: | 31 |
| Uncontrolled Keywords: | quantum-mechanical exchange iridium trihydride complexes molecular-hydrogen complexes nuclear-magnetic-resonance solid-state spectroscopic properties temperature-dependence dynamic nmr couplings tautomerism |
| Divisions: | 07 Department of Chemistry 07 Department of Chemistry > Physical Chemistry |
| Date Deposited: | 27 Oct 2014 20:45 |
| Official URL: | http://apps.webofknowledge.com/full_record.do?product=WOS&se... |
| Additional Information: | 111CQ Times Cited:34 Cited References Count:83 |
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