Synthesis, Structural Characterization, and Guest Exchange Properties of Hydrogen-Bonded Organic Frameworks Based on Bis(benzimidazole)ZnCl<sub>2</sub> Complexes
Yurika Iwabuchi, Ryoga Yamaguchi, Tatsunari Murakami, Masaaki Okazaki, Shun Ohta
Abstract
Hydrogen-bonded organic frameworks (HOFs) based on coordination compounds constitute a developing class of interesting porous materials. Herein, we report on the synthesis, crystal structures, and guest exchange properties of four HOFs based on zinc dichlorido complexes that bear a bis(benzimidazolyl)methane ligand (bis(benzimidazole)ZnCl2). The porous structures of these bis(benzimidazole)ZnCl2-based HOFs are characterized predominantly by intermolecular N–H···Cl hydrogen bonds in conjunction with π–π interactions. One of these HOFs was found to exchange guest molecules via single-crystal-to-single-crystal transformations with or without structural change. A single-crystal X-ray diffraction study revealed that the guest exchange accompanied by a structural change is induced by the cleavage of the N–H···Cl hydrogen bonds between the bis(benzimidazole)ZnCl2 complexes, followed by the formation of alternate hydrogen bonds with guest molecules. This result suggests that the use of weaker N–H···Cl hydrogen bonds than those typically used for the construction of HOFs (e.g., carboxylic acid dimers, N-heterocycles, and charge-assisted moieties) may represent a convenient strategy to synthesize flexible HOFs.