Reversible Adsorption of Ammonia in the Crystalline Solid of a CO 2 H-Functionalized Cyclic Oligophenylene

Ammonia (NH ) is a viable candidate for the storage and distribution of hydrogen (H ) due to its exceptional volumetric and gravimetric hydrogen energy density. Therefore, it is desirable to develop NH storage materials that exhibit robust stability across numerous adsorption-desorption cycles. While porous materials with polymeric frameworks are often used for NH capture, achieving reversible NH uptake remains a formidable challenge, primarily due to the high reactivity of NH . Here, we advocate the use of CO H-functionalized cyclic oligophenylene with high chemical stability as a novel single-molecule-based adsorbent for NH . Simple reprecipitation of selectively yielded microporous crystalline solid ( ). Crystalline ( ) adsorbs up to 8.27 mmol/g of NH at 100 kPa and 293 K. Adsorbed NH in the pore of ( ) has a packing density of 0.533 g/cm at 293 K, which is close to the density of liquid NH (0.681 g/cm at 240 K). Crystalline ( ) also exhibits reversible NH adsorption over at least nine cycles, sustaining its storage capacity (1st cycle: 8.27 mmol/g; 9th cycle: 8.25 mmol/g at 100 kPa and 293 K) and crystallinity. During each desorption cycle, NH was removed from ( ) under reduced pressure (∼65 Pa), leaving