The optimized stable CH3SH…HOCl hydrogen bond and CH3SH…ClOH halogen bond complexes were located on the potential energy surface by means of DFT-B3LYP/6-311＋＋G**. The obvious red shifts of the H(8)—O(7) and Cl(9)—O(7) stretching vibrational frequencies in the two complexes were observed via frequency analysis. The halogen bond interaction energy of CH3SH…ClOH was －6.85 kJ•mol－1, and the hydrogen bond interaction energy of CH3SH…HOCl was －19.23 kJ•mol－1, which were calculated with basis set superposition error (BSSE) correction via a counterpoise procedure (CP) method. Natural bond orbital (NBO) theory analysis showed that two kinds of charge transfers exist in the CH3SH…ClOH halogen bond system: (i) lone pair LP[S(1)]1→σ*[Cl(9)—O(7)]; (ii) lone pair LP[S(1)]2→σ*[Cl(9)—O(7)], and the natural population of the σ*[Cl(9)—O(7)] increased. Analogous charge transfers exist in the CH3SH…HOCl hydrogen bond complex. The bond order analysis with natural resonance theory (NRT) showed that bond order of Cl(9)—O(7) in the CH3SH…ClOH halogen bond complex and that of H(8)—O(7) in the CH3SH…HOCl hydrogen bond complex both decreased. The topological properties of the hydrogen bond and halogen bond structures were also investigated by the atoms-in-molecules (AIM) theory.

Key words: CH3SH, HOCl, hydrogen bond, halogen bond, natural bond orbital theory, atoms-in-molecules theory