Guest Exchange as a Synthetic Strategy for Hydrogen-Bonded Organic Frameworks

Hydrogen-bonded organic frameworks (HOFs) are mainly synthesized via recrystallization from solutions that contain molecular building blocks; however, this is not an infallible strategy. For example, the formation of hydrogen bonds between the building blocks and molecules of the crystallization solvent may prevent the construction of the frameworks. Herein, we propose a guest- exchange-based strategy for converting non-HOF crystals to HOFs. Specifically, non-HOF crystals of bis(benzimidazole)ZnCl2 complex 1 (bis(benzimidazole) = phenylbis(benzimidazol-2-yl)methane) obtained from its N,N-dimethylformamide (DMF) solution (12·(DMF)5) were converted to HOF crystals via the exchange of DMF to acetone or tetrahydrofuran by exposing 12·(DMF)5 to the corresponding vapor. Interestingly, the complete guest exchange is not always required, which further emphasizes the convenience of the guest-exchange strategy in HOF synthesis. We also demonstrate that HOF crystals synthesized via guest exchange can serve as an adsorber for acetone and diethyl- ether vapors.