Calix[4]arene-5,17-dicarboxylic acids and their interactions with aliphatic amines. Part 2. A crystal engineering approach

Abstract

The possible interactions between diacid functionalised conformationally diverse calix[4]arene molecules and simple amines were investigated. The aim was to establish an understanding of the solid state constructions obtained upon crystallising the salts formed between the acids and the amines. Each component of the acid–base system was subject to variations through the degree of chemical substitution and conformational diversity of the calix[4]arene system and through the degree of chemical substitution for the amine system pertaining to primary, secondary and tertiary amines. Unlike the known solution behaviour where tertiary amines behave differently from secondary and primary amines as a group it was found that the solid state behaviour was further differentiated. In the solid state primary amines give rise to salt bridged closed networks whereas secondary amines give rise to open polymeric salt bridged networks and tertiary amines give rise to monomeric salts. Furthermore the patterns that were uncovered from the isolated studies could be used to predict the structural behaviour of a more complex case such as the biological molecule ephedrine for which a calix[4]arene based sensing system was developed in our previous paper.