Desolvation-Induced Network Reformation and Cracking in the Single Crystals of Hydrogen-Bonded Frameworks Composed of Tetraazaanthraquinone and Anthraquinone Derivatives.

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 tetraazaanthraquinone 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.