Exploiting the σ-Hole Concept: An Infrared and Raman-Based Characterization of the S⋅⋅⋅O Chalcogen Bond between 2,2,4,4-Tetrafluoro-1,3-dithiethane and Dimethyl Ether.

Abstract

In the last decade, halogen bonds, noncovalent interactions formed between positive regions in the electrostatic potential on halogen atoms, often referred to as σ-holes, and electron-rich sites, have gained a lot of interest. Recently, this interest has been expanded towards interactions with Group V and Group VI elements, giving rise to pnicogen and chalcogen bonds. Although chalcogen bonds have already shown some promising results for applications in crystallography and catalysis, experimental results characterising these noncovalent interactions remain scarce. In this combined experimental and theoretical study, original data allowing the characterization of S⋅⋅⋅O chalcogen bonds is obtained by studying the 1:1 molecular complexes between 2,2,4,4-tetrafluoro-1,3-dithiethane (C2 F4 S2 ) and dimethyl ether (DME). Ab initio calculations of the C2 F4 S2 ⋅DME dimer yield two stable chalcogen-bonded isomers, the difference being the presence or absence of secondary F⋅⋅⋅H interactions. Liquid-krypton solutions containing C2 F4 S2 and DME were studied using FTIR and Raman spectroscopy. Upon subtraction of rescaled monomer spectra, clear complex bands are observed. The observed complexation shifts agree favourably with the ab initio calculated shifts of the chalcogen-bonded complexes. The 1:1 stoichiometry of the complex is confirmed and a complexation enthalpy of -13.5(1) kJ mol-1 is found, which is in good agreement with the calculated values. A Ziegler-Rauk energy decomposition analysis revealed that electrostatic interactions prominently dominate over orbital interactions. Nevertheless, significant charge transfer occurs from the oxygen in DME to one of the sulfur atoms in C2 F4 S2 and the carbon along the extension of the chalcogen bond.