Hexameric assembly of 5,17-di-substituted calix[4]arene in the solid state

Abstract

Chiral 5,17-difunctionalized-25,26,27,28-tetrapropyloxycalix[4]arene possessing (S)-mandelamide arms ((S,S)-1) afforded cocrystals (S,S)-1·(solvent) (solvent = MeOH, EtOH, 1-PrOH, 2-PrOH, and CH₃CN). X-ray diffraction analysis revealed that (S,S)-1 formed head-to-tail columnar structures. In most cocrystals (MeOH, EtOH, 1-PrOH, and CH₃CN), the columnar structures were arranged hexamerically to form a chiral hexagonal channel, which is a rare example of calix[4]arene derivatives in the solid state. The fact that the branched guest (2-PrOH) and the racemic mixture of the host formed different crystal packings wherein no hexameric structure existed indicates that both the linearity of the guest and the homochirality of the host are important factors for driving the columnar structures to form the hexameric assembly. Apohost (S,S)-1_apo showed interesting adsorption behavior; it adsorbed benzene among the organic molecules tested. The adsorption and desorption processes were repeated several times, demonstrating the sponge-like character of (S,S)-1_apo.