The high-level G4(MP2) composite method and B2-PLYP double-hybrid density functional theory have been used to investigate interactions of all-cis hexafluorocyclohexane and hexachlorocyclohexane molecules with a series of anions and cations in the gas phase. The calculated binding enthalpies are exceptionally high for bound complexes formed between these ions and molecular species. The binding energies of Cl- to all-cis hexafluorocyclohexane and all-cis hexachlorocyclohexane obtained at the G4(MP2)[B2-PLYP] theoretical level are 159.3 [159.6] and 149.3 [147.7] kJ mol(-1), respectively. Similar observations are made for some of the other considered complexes. We also show that for anionic complexes, the strongest complexes are formed with all-cis hexachlorocyclohexane rather than with all-cis hexafluorocyclohexane. However, for cationic complexes, an opposite behaviour is observed, with the exception of some cations such as Mg2+ and Zn2+.
