Unveiling the structural features of the host–guest complexes of carboxylated pillar[5]arene with viologen derivatives

Abstract

Despite the impressive progress in the study of the aqueous host–guest chemistry of carboxylated pillar[n]arenes, these macrocyclic molecules represent a completely unexplored class of molecular building blocks in the solid state supramolecular chemistry. Here we describe the formation of crystalline host–guest complexes of carboxylated pillar[5]arene with four viologen derivatives, emphasizing its inclusion and self-assembly behavior in the presence of cationic electron-deficient guests. The macrocyclic cavity is prone to slight distortion upon the inclusion of alkyl viologens, but competitive inclusion of ethanol molecules takes place in the case of bulky benzyl viologen. The different distribution of carboxylic versus carboxylate substituents of pillar[5]arene renders self-assembly via carboxylic–carboxylic or carboxylic–carboxylate supramolecular synthons.