Structural Control of Metal-Organic Framework Bearing N-Heterocyclic Imidazolium Cation and Generation of Highly Stable Porous Structure.

Building a well-defined porous structure with permanent porosity in a metal-organic framework (MOF) is significant to achieve selective adsorption of guest molecules and its practicality. There have been various efforts to develop new functional frameworks, but chasing both advantages (functions and stability) is always challenging. Herein, we report a highly stable and porous 3D MOF having an imidazolium group. By adjusting counteranions of the imidazolium group, we could prepare two distinct MOFs. The 2D MOF constructed by applying bicarbonate anion inhibited three-dimensional growth and showed N adsorption with BET results of 330 m/g. However, the 3D MOF (Imi-3D) formed by applying chloride anion on the imidazolium group evolved into a 4-fold interpenetrated cube structure. The Imi-3D has high porosity in spite of the folded nature of the structure, with BET results of 1400 m/g. Interestingly, unlike the usual trend of unstable zinc carboxylate based MOFs, the multiple π-π interactions of the Imi-3D presents a unique tolerance toward various solvents, especially toward water, for 6 months and without decomposition or collapse of the framework. Moreover, since the porous 3D MOF consists of imidazolium groups, the MOF shows a cationic feature with strong adsorption toward anionic guests in aqueous media.