Cation-π Interactions in Calix[4]arene-based Host Molecules. What Kind of Cavity-shape ls Favored for the Cation-binding?

The cation-π interaction was studied using 9 calix[n]arenes with the different cavity size and the different cavity shape: the efficient binding of N-methylpyridinium iodide was observed for calix[6]arenes among calix[n]arenes and for cone isomers among calix[4]arene conformers, indicating the importance of the host-guest-type cation inclusion in the π-base cavities.