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Toluene was discovered as the structure template for the synthesis of large-cage RHO-type zeolitic imidazolate frameworks (ZIF-11 and ZIF-12) in an alcohol-based solution where benzimidazole-toluene interactions play a decisive structure-directing role; otherwise it leads to small-cage SOD-type ZIF-7 and ZIF-9 without toluene. The specific π-π interactions make toluene molecules adopt a specific and oriented arrangement in the unit cell. XRD intensity of the (100) plane is strongly dependent on the amount of toluene: apparent intensity degradation is observed after removing toluene by solvent exchange or thermal treatment, and the peak intensity is recoverable by filling of the pores with toluene vapor. More-polar methanol as compared to ethanol is favorable for the formation of RHO-type ZIFs due to the enhanced interactions between toluene and imidazolate linkers.

Zeolitic imidazolate frameworks (ZIFs) have attracted considerable attention for many potential applications because they have a unique porous structure and excellent thermal and chemical stabilities. In recent years, significant efforts have been made to develop different methods for the controllable synthesis of ZIFs with desirable crystal structure and morphologies, and for decreasing the excessive amounts of organic ligands and solvents used in the synthesis process to reduce the costs and environmental impacts. This paper highlights the strategies recently reported, including the controllable synthesis of ZIFs with desirable morphologies and pore structure using a surfactant and a template in aqueous solution, the synthesis of ZIF particles and nanocrystals in base solution, and the dry gel and mechanochemical syntheses of ZIFs with minimal solvent usage. [ABSTRACT FROM AUTHOR]