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Issue 30, 2019
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The S∴π hemibond and its competition with the S∴S hemibond in the simplest model system: infrared spectroscopy of the [benzene-(H2S)n]+ (n = 1–4) radical cation clusters

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Abstract

The S∴π hemibond (two-center three-electron, 2c-3e, bond) is an attractive interaction between a sulfur atom and π electrons. The S∴π hemibond is of essential importance in understanding chemistry of sulfur radical cations, and its roles in biochemistry have recently attracted much interest. In the present study, we observe the S∴π hemibond in the simplest model system in the gas phase. Infrared spectroscopy is applied to the [benzene-(H2S)n]+ (n = 1–4) radical cation clusters. In n = 1, the CH stretch and SH stretch bands of the benzene and H2S moieties, respectively, are clearly different from those of the neutral molecules but similar to those of the ionic species. These vibrational features show that the positive charge is delocalized over the cluster due to the S∴π hemibond formation. In n = 2–4, the S∴S hemibond and S–π–S multicenter hemibond (three-center five-electron, 3c-5e, bond) can compete with the S∴π hemibond. The observed vibrational features clearly indicate that the S∴S hemibond formation is superior to the S∴π hemibond and S–π–S multicenter hemibond. Calculations of several dispersion-corrected density functionals are compared with the observations. While all the tested functionals qualitatively catch the feature of the S∴π hemibond, the energy order among the isomers of the different hemibond motifs strongly depends on the functionals. These results demonstrate that the [benzene-(H2S)n]+ clusters can be a benchmark of density functionals to evaluate the sulfur hemibonds.

Graphical abstract: The S∴π hemibond and its competition with the S∴S hemibond in the simplest model system: infrared spectroscopy of the [benzene-(H2S)n]+ (n = 1–4) radical cation clusters

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Publication details

The article was received on 21 May 2019, accepted on 19 Jun 2019 and first published on 19 Jun 2019


Article type: Edge Article
DOI: 10.1039/C9SC02476J
Chem. Sci., 2019,10, 7260-7268
  • Open access: Creative Commons BY license
    All publication charges for this article have been paid for by the Royal Society of Chemistry

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    The S∴π hemibond and its competition with the S∴S hemibond in the simplest model system: infrared spectroscopy of the [benzene-(H2S)n]+ (n = 1–4) radical cation clusters

    D. Wang, K. Hattori and A. Fujii, Chem. Sci., 2019, 10, 7260
    DOI: 10.1039/C9SC02476J

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