Hydrogen-Bonded Ladder Frameworks Composed of Low Symmetric Tricarboxylic Acids

Abstract

Preorganization of supramolecular network structures by designing building block molecules from aspects of supramolecular synthons and tectons is fundamental for developing porous organic materials. Benzene derivatives possessing 4-carboxyphenyl groups are suitable systems to explore the relationship between the symmetry of tectons and the resultant supramolecular network structures because of directional hydrogen bonding of the carboxy groups. Herein, supramolecular network structures composed of C_s-symmetric 1,2,4-tris(4-carboxyphenyl)benzene and its analogues with pyridine and isoquinoline cores are reported. These tritopic carboxylic acids form a ladder-shaped motif instead of a brick-type network motif via intermolecular hydrogen bonding. Their crystal structures and thermal behaviors are thoroughly investigated, revealing that they showed multistep structural transformations upon release of the solvent molecules included in their voids. The behaviors strongly depend on the cores. These results can contribute to the field of reticular chemistry from aspects of molecular symmetry and the resultant network topology.