Chemical origin of contracted C-Cl bonds in the halogen-bonded complexes

In this paper, we calculated a series of halogen-bonded complexes. The halogen bond donor is CFnH3−nCl, and the halogen bond acceptors are NH3, H2O, H2S, and Br−. Ten stable halogen-bonded complexes were obtained and the C-Cl bond length was contracted in all of these complexes. We carried out AIM and NBO analysis under the MP2/aug-cc-PVDZ optimized structures. The variation of the electron density at the bond critical point of C-Cl bond correlates well with Δr(C-Cl). A balance among intra- and inter-hyperconjugation and rehybridization determined the contracted C-Cl bond.