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NMR and INS line shapes of transition metal hydrides in the presence of coherent and incoherent dihydrogen exchange

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.
120, In: Journal of the American Chemical Society, (31), pp. 7929-7943, [Online-Edition: http://apps.webofknowledge.com/full_record.do?product=WOS&se...],
[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
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...
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111CQ Times Cited:34 Cited References Count:83

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