Influence of molecular electronic properties on the IR spectra of dimeric hydrogen bond systems: polarized spectra of 2-hydroxybenzothiazole and 2-mercaptobenzothiazole crystals |
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Authors: | Henryk T Flakus Artur MirosPeter G Jones |
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Institution: | a Institute of Chemistry, University of Silesia, 9 Szkolna Street, Pl-40006 Katowice, Poland b Institut f(ür Anorganische und Analytische Chemie, Technische Universität Braunschweig, Postfach 3329, Braunschweig 38023, Germany |
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Abstract: | We have studied the polarized IR spectra of the hydrogen-bonded molecular crystals of 2-hydroxybenzothiazole (HBT) and 2-mercaptobenzothiazole (MBT). The crystal structure of 2-hydroxybenzothiazole was determined by X-ray diffraction. The polarized spectra of the crystals were measured, in the frequency ranges of the νN-H and νN-D bands, at room temperature, and at 77 K. In both systems an extremely strong H/D isotopic effect in the spectra was observed, involving reduction of the well-developed νN-H band fine structure to a single prominent νN-D line only. The two νN-H bands were also shown to exhibit almost identical properties, band shapes, temperature and dichroic properties included. The spectra were quantitatively reconstituted, along with the strong isotopic effect, when calculated using the ‘strong-coupling’ theory, assuming the centrosymmetric dimers of HBT or MBT to be the structural units responsible for the crystalline spectral properties. The similarity of the spectra of the two crystalline systems was considered to be a result of longer-distance couplings between the proton vibrations in the dimers, via the aromatic ring electrons. When investigating the ‘residual’ νN-H band shapes for crystals isotopically diluted by deuterium, we observed some ‘self-organization’ effects in the spectra, indicating the energetically favored presence of two identical hydrogen isotopes in each hydrogen bond dimer. |
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Keywords: | Hydrogen bond Molecular crystals Polarized spectra in the IR Isotopic effects Temperature effects Strong-coupling model Electronic effects Self-organization effects |
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