Competition and cooperativity between hydrogen bond and σ-hole bond in SCS-(HF)n (n = 1 and 2) systems

Quantum chemical calculations have been performed for 1:1 and 1:2 systems of SCS and HF at the MP2/aug-cc-pVTZ level. There are two isomers for SCS-HF dimer. One is combined through a hydrogen bond with SCS as the electron donor; the other is formed by a σ-hole bond with SCS as the electron acceptor. Although the σ-hole bond is weaker than the hydrogen bond, the former is still competitive with the latter in this system. For comparison, the OCO-HF, SeCSe-HF, and SCS-HCl systems have also been analyzed. The most stable structure is the trimer where there are a FH⋯S hydrogen bond and a direct HF-HF contact simultaneously. It is shown that there is a cooperative effect between the hydrogen bond and the σ-hole bond. The band of 3843 cm−1 is assigned to the H-F stretch vibration in the σ-hole-bonded dimer. The natural bond orbital (NBO) and atoms in molecules (AIM) analyses have been performed for a better understanding the interactions.