A comparative study of the chalcogen bond, halogen bond and hydrogen bond S⋯O/Cl/H formed between SHX and HOCl.

Ab initio quantum chemistry methods were used to analyze the noncovalent interactions between HOCl and SHX (X = F, CN, NC, Cl, Br, NO2, CCH, CH3, H). Three energetic minimal configurations were characterized for each case, where the S center acts as a Lewis acid interacting with O to form a chalcogen bond, as well as a Lewis base interacting with Cl or H of HOCl to form halogen bond and hydrogen bond, respectively. An electronegative substituent such as F, CN, NC and NO2 tends to form a stronger chalcogen bond, while an electropositive substituent such as CCH, CH3 and H is inclined to form a more stable H-bonded complex. The chalcogen-bonded, halogen-bonded and H-bonded complexes are stabilized by charge transfers from Lp(O) to σ*(SX), from Lp(S) to σ*(ClO), and from Lp(S) to σ*(HO), respectively. As a result, the SHX unit becomes positively charged in halogen-bonded and hydrogen-bonded complexes but negatively charged in chalcogen-bonded complexes. Theory of atoms in molecules, natural bond orbital analysis, molecular electrostatic potential and localized molecular orbital energy decomposition analysis were applied to investigate these noncovalent bonds.