Solvent-etching-induced in situ crystal structure transformation in hydrogen-bonded organic frameworks

Abstract

In situ crystal structure transformation is an important method for the emergence of new structures. Currently, there are very limited reports on crystal structure transformation in hydrogen-bonded organic frameworks (HOFs), and such transformation only occurs in response to external stimulation. Herein, we report a rare solvent-etching-induced in situ crystal structure transformation in UPC-HOF-12 and UPC-HOF-13 (UPC-HOF = China University of Petroleum-hydrogen-bonded organic framework). Remarkably, molecule recognition is observed in the crystal structure transformation, i.e., only N,N′-dimethylformamide (DMF) as the etching agent can cause the in situ crystal structure transformation, as evidenced by the consecutive changes in crystal morphology and time-dependent powder X-ray diffraction patterns. Simultaneous cleavage and regeneration of the flexible and fragile hydrogen bonds are observed with the determination of the single crystal structures. This rare example of solvent-etching-induced in situ crystal structure transformation with maintained crystallinity after crystal fragmentation can provide a new perspective for elucidating the crystal growth process in HOFs.