An ab initio investigation of some hydrogen-bonded complexes of methanethiol

The hydrogen-bonded complexes formed between methanethiol, as proton donor, and trimethyl amine, dimethyl ether, methyl fluoride, trimethyl phosphine, dimethyl sulphide and methyl chloride, as proton acceptors, have been studied by means of ab initio calculations at the second order level of Møller-Plesset perturbation theory and using the 6-311++G(d,p) basis set. The hydrogen bond energies were found to correlate with the gas phase basicities of the proton acceptors. The increases of the SH bond lengths, the shifts of the wavenumbers of the SH stretching modes and the increases of their infrared intensities were also found to be dependent on the interaction energies. The results for the CH3SH·S(CH3)2 complex are anomalous, and this is attributed to deficiencies with the basis set used for sulphur. The data for the CH3SH complex closely mirror the behaviour of the corresponding complexes of CH3OH and (CH3)2NH, with the perturbations of the various properties varying consistently in the order CH3OH > (CH3)2NH > CH3SH.