Competitive inclusion of disubstituted benzene regioisomers with crystals of p-tert-butylcalix[4]arene

A crystal of p-tert-butylcalix[4]arene (1) has selectively included regioisomers of eight different disubstituted benzenes, giving inclusion crystals classified into four types: 2:1 (host/guest) with p-isomer and 1:1 with o-, m-, and p-isomers. X-ray crystallographic analysis of 1₂p-xylene, 1ocresol, 1m-dichlorobenzene, and 1p-chlorotoluene, which were chosen as representatives for the individual types of inclusion crystals, revealed that the electrostatic properties and steric bulk of the substituents in the rigid guest molecules are efficiently reflected in the interaction with the host molecules, which construct flexible bilayer-based packing structures in the inclusion crystals. This is considered as a principal origin for the high selectivity and wide applicability achieved in the inclusion of aromatic regioisomers with crystals of compound 1.