Charge-Neutral N–H···Br as a Hydrogen-Bond Family for the Construction of Hydrogen-Bonded Organic Frameworks

Abstract The design, synthesis, and application of porous molecular crystals constructed using intermolecular hydrogen bonds (hydrogen-bonded organic frameworks; HOFs) have attracted significant attention due to the potential flexibility and solution processability of HOFs, which arise from the nature of hydrogen bonds. HOFs are generally constructed via highly directional intermolecular N–H···N and O–H···O hydrogen bonds, while the study of HOFs constructed by low-directional hydrogen bonds has lagged somewhat. The present study reveals that charge-neutral N–H···Br hydrogen bonds are suitable for the construction of HOFs. Specifically, single crystals of a bis(benzimidazole)NiBr2 complex (bis(benzimidazole) = phenylbis(benzimidazol-2-yl)methane) were found to be a HOF supported by intermolecular N–H···Br hydrogen bonds. This HOF exhibits interesting flexibility, i.e., the intermolecular N–H···Br hydrogen bonds are cleaved and reformed upon the adsorption/desorption of organic vapors. Moreover, it can adsorb organic vapors in a recyclable fashion (for at least 10 cycles when acetone is used). This study expands the classes of low-directional hydrogen bonds applicable to the construction of HOFs.