Assembly of calix[4]arene carboxylic acid derivatives by hydrogen bonding

Abstract

The crystal structures of cone-tetra-O-propoxy-tetra-p-carboxylatocalix[4]arene·tetrahydrofuran (1·THF), cone-di-O-isopropoxy-tri-p-carboxylatocalix[4]arene·tetrahydrofuran (6·THF) and cone-di-O-isopropoxy-tri-p-carboxylatocalix[4]arene·tetrahydrofuran·methanol (6·THF·MeOH) in THF–MeOH as a mixed solvent for crystallization, and the crystal structures of 1,3-alt-tetra-O-propoxy-tetra-p-carboxylatocalix[4]arene (7), 1,3-alt-tetra-O-isopropoxy-tetra-p-carboxylatocalix[4]arene·pyridine (8·Py), 1,3-alt-tetra-O-isopropoxy-tri-p-carboxylatocalix[4]arene·methanol (9·MeOH), 1,2-alt-A,C-di-O-benzoyl-di-p-carboxylatocalix[4]arene (10) and 1,2-alt-A,B-di-O-benzoyl-di-p-carboxylatocalix[4]arene·methanol (11·MeOH) in Py–MeOH as a mixed solvent for crystallization have been investigated. The effects of the following factors on the self-assembly of the calixarene derivatives have been studied: (1) crystallization solvent, (2) the conformation of the calixarene, and (3) steric hinderance of the substituents at the lower rim of the calixarene. The results indicate that different supramolecular aggregate structures could be obtained in different types of solvent or proportions of the mixed solvent. 1,3-alternate calixarenes could easily form a nanometer scale capsule-like structure based on their own cavities. The carboxyl group in the upper rim would dominate the self-assembly of the calixarene, and all of the compounds except for compound 8 form a head-to-head or head-to-tail dimer through type I hydrogen bonds. As an exception, compound 8 forms a head-to-head dimer through type II hydrogen bonds between Py molecules and the macrocyclic molecule.