Halogen bonding to a divalent sulfur atom: an experimental study of the interactions of CF3X (X = Cl, Br, I) with dimethyl sulfide

Abstract

Using FTIR and Raman spectroscopy, the formation of halogen bonded complexes of the trifluorohalomethanes CF₃Cl, CF₃Br and CF₃I with dimethyl sulfide (DMS) dissolved in liquid krypton has been investigated. For CF₃Br and CF₃I, evidence was found for the formation of C–X⋯S halogen bonded 1 ∶ 1 complexes. At higher concentrations of CF₃I weak absorptions due to a 2 ∶ 1 complex were also observed. Using spectra recorded at temperatures between 118 and 163 K, the complexation enthalpies for the complexes were determined to be −9.5(5) kJ mol⁻¹ for CF₃Br·DMS, −17.4(1) kJ mol⁻¹ for CF₃I·DMS and −30.8(16) kJ mol⁻¹ for (CF₃I·)₂DMS. The results from the cryospectroscopic study are compared with ab initio calculations at the MP2/aug-cc-pVDZ(-PP) level. Apart from vibrational modes localized in the trifluorohalomethanes and the DMS moieties, for both CF₃Br and CF₃I, an additional band, which we assign as the intermolecular stretching mode in the complex, was identified in the infrared and Raman spectra.