Ionic liquids have attracted a great deal of interest in recent years, illustrated by their applications in a variety of areas involved with chemistry, physics, biology, and engineering. Usually, the stabilities of ionic liquids are highlighted as one of their outstanding advantages. However, are ionic liquids really stable in all cases? This review covers the chemical stabilities of ionic liquids. It focuses on the reactivity of the most popular imidazolium ionic liquids at structural positions, including C2 position, N1 and N3 positions, and C4 and C5 positions, and decomposition on the imidazolium ring. Additionally, we discuss decomposition of quaternary ammonium and phosphonium ionic liquids and hydrolysis and nucleophilic reactions of anions of ionic liquids. The review aims to arouse caution on potential decomposition of ionic liquids and provides a guide for better utilization of ionic liquids.

Research on ionic liquids has achieved rapid progress in the last several decades. Stability is a prerequisite for the application of ionic liquids. Ionic liquids may be used at elevated temperature, as electrolytes, or under irradiation. Therefore, the thermal, electrochemical, and radiolytic stabilities of ionic liquids are important and need to be known before their usage. Many research papers and some reviews on the stabilities of ionic liquids have been published. However, new results are continuously being published and a comprehensive review and perspective on this topic are still urgently needed. In this perspective, we intend to provide a comprehensive review including characterization methods, the effects of chemical composition of the ionic liquids on the thermal, electrochemical, and radiolytic stabilities of ionic liquids, respectively. Moreover, the thermal stability of some special types of ionic liquids such as poly(ionic liquids) and mixed ionic liquids, and the thermal and electrochemical stabilities of protic ionic liquids are discussed too. For thermal stability, the interactions between ions are less important than the individual anions and cations. The decomposition temperature is mainly determined by the less-stable ion, usually the anion. For electrochemical stability, the electrochemical window is determined by both the cation and anion. The less stable ion could influence the stability by interaction between the generated species from the decomposition with the more stable ion (opposite ion). This perspective is helpful for people to avoid using unstable ionic liquids and choose suitable ionic liquids.

The mesoporous metal–organic frameworks are a family of materials that have pore sizes ranging from 2 to 50 nm, which have shown promising applications in catalysis, adsorption, chemical sensing and so on. The preparation of mesoporous metal–organic frameworks usually needs the supramolecular or cooperative template strategy. Here we report the template-free assembly of mesoporous metal–organic frameworks by using CO2-expanded liquids as switchable solvents. The mesocellular metal–organic frameworks with large mesopores (13–23 nm) are formed, and their porosity properties can be easily adjusted by controlling CO2 pressure. Moreover, the use of CO2 can accelerate the reaction for metal–organic framework formation from metal salt and organic linker due to the viscosity-lowering effect of CO2, and the product can be recovered through CO2 extraction. The as-synthesized mesocellular metal–organic frameworks are highly active in catalysing the aerobic oxidation of benzylic alcohols under mild temperature at atmospheric pressure.