A theoretical study of the interactions of iodo-perfluorocarbon and iodo-hydrocarbon with haloid anions

Ab initio calculations have been performed on a series of complexes formed between iodo-perfluorocarbons(PFCs) and iodo-hydrocarbons(HCs) and haloid anions to gain a deeper insight into the nature of halogen bonds. It appears that halogen bonds in these complexes are much stronger than neutral halogen bonds. Calculations also show that the strength of halogen bonds in iodo-PFC⋯haloid anion dimers are greater than those in iodo-HC⋯haloid anion dimers. A comparison of the two complex series reveals that the hybridization state of the carbon atom bonded to iodine has a less pronounced effect on the interatomic distances I ⋯ X in the iodo-PFC series in relation to the iodo-HC series. PCM calculations used to investigate the solvent effect on halogen bonds unveil that, in the gas phase, fluorine anion prefers to form halogen-bonded complexes with respect to chloride, bromide, and iodine anions; however, the preference is not obvious, and even an opposite order is observed in solutions. It is worth mentioning that the iodo-PFC⋯fluorine anion complexes present a special structure, i.e. the interatomic I⋯F distances in these complexes are relatively short and the corresponding C-I bonds tend to be further broken. These features, in combination with the geometrical data, indicate that ate-complexes are formed between iodo-PFC and fluorine anions.