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

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.