Desolvation‐Induced Network Reformation and Cracking in the Single Crystals of Hydrogen‐Bonded Frameworks Composed of Tetraazanthraquinone and Anthraquinone Derivatives

Abstract

A molecular‐level understanding of how structural transformations induce morphological changes in organic crystals is essential for developing flexible crystalline materials. Herein, we report that two solvated hydrogen‐bonded organic frameworks (HOFs) undergo structural transformations, giving rise to crystal crack propagation in the directions corresponding to their molecular displacements. The HOFs are composed of the tetracarboxylic acids, 4,4',4'',4'''‐(5,10‐dioxo‐5,10‐dihydropyrazino[2,3‐g]quinoxaline‐2,3,7,8‐tetrayl)tetrabenzoic acid (TAAQ) and 4,4',4'',4'''‐(9,10‐dioxo‐9,10‐dihydroanthracene‐2,3,6,7‐tetrayl)tetrabenzoic acid (AQ), incorporating tetraazanthraquinone and anthraquinone cores, respectively. Although TAAQ and AQ have closely similar molecular geometries, their HOFs have entirely different hydrogen‐bonded networks. In both HOFs, we found that specific directional hydrogen bonds cleaved, and new hydrogen bonds re‐formed, resulting in quasi single‐crystal‐to‐single‐crystal transformations. The direction of molecular displacement and crystal cell shrinkage were aligned parallel to the crack propagation. These results contribute to a deeper understanding of the underlying micro‐macro property correlations induced by hydrogen bond cleavage and re‐formation.