Enhancing the binding of calix[5]arene containers for ferrocenes by a fluorophobic effect through the release of high-energy perfluoro-1-iodoalkanes†

A hydrogen bonded calix[5]arene cavitand has been designed and prepared, which has a bowl-like cavity of about 0.85 nm width. The binding affinity of the container for ferrocene and eight of its derivatives in chloroform is modest. In a binary perfluoro-1-iodohexane and chloroform mixture (9 : 1 v/v), binding constants for the complexes of the seven fluorine-free guests increase by 14.0–144.1 times. In contrast, binding constants for the complexes of two guests that bear a perfluoroheptyl group do not exhibit similar increases. Similar enhancement of binding affinity can also be observed in binary solvents of perfluoro-1-iodobutane or perfluoro-1-iodooctane and chloroform. The results support that perfluoro-1-iodoalkanes in the cavity of the calix[5]arene container function as high-energy solvent molecules and their release into the bulk phase is the major driving force for enhanced inclusion by the calix[5]arene container of the fluorine-free guests.