Functionality-Induced Locking of Zeolitic Imidazolate Frameworks

Zeolitic imidazolate frameworks (ZIFs) are metal- organic analogues of zeolites that have attracted considerable interest for gas separation applications. However, the inherent framework flexibility of ZIFs during gas adsorption complicates their designed and desired performance. Herein, we report functionality-induced locking of ZIFs undergoing irreversible structural transformations, which leads to exceptional framework rigidity. Specifically, an isoreticular series of zeolite GME-type CoII- ZIFs were prepared and proven to have dynamic, flexible, and rigid behaviors after thermal activation, depending on their functional groups (i.e., -H, -CH3, and -NO2). Molecular insights into the irreversible, functionality-induced locking were determined to occur as a consequence of framework flexibility for maximizing the linker-linker interactions from pi-pi interaction to hydrogen bonding. The practical impact of functionality-induced locking in ZIFs was evaluated through high-pressure CO2/CH4 adsorptive separation for realizing more efficient methane purification. The present findings shed light on the deliberate control over the inherent flexibility observed in many porous materials to optimize their performance in practical applications.