Tetrahedral Imidazolate Frameworks with Auxiliary Ligands (TIF-Ax): Synthetic Strategies and Applications

Zeolitic imidazolate frameworks (ZIFs) are an important subclass of metal-organic frameworks (MOFs). Recently, we reported a new kind of MOF, namely tetrahedral imidazolate frameworks with auxiliary ligands (TIF-Ax), by adding linear ligands (Hint) into the zinc-imidazolate system. Introducing linear ligands into the M2+-imidazolate system overcomes the limitation of imidazole derivatives. Thanks to the synergistic effect of two different types of ligands, a series of new TIF-Ax with interesting topologies and a special pore environment has been reported, and they have attracted extensive attention in gas adsorption, separation, catalysis, heavy metal ion capture, and so on. In this review, we give a comprehensive overview of TIF-Ax, including their synthesis methods, structural diversity, and multi-field applications. Finally, we also discuss the challenges and perspectives of the rational design and syntheses of new TIF-Ax from the aspects of their composition, solvent, and template. This review provides deep insight into TIF-Ax and a reference for scholars with backgrounds of porous materials, gas separation, and catalysis.

Metal-Organic Framework with Structural Flexibility Responding Specifically to Acetylene and Its Adsorption Behavior

Flexible metal-organic frameworks (MOFs) are one kind of stimuli-responsive materials that exhibit reversible structural transformations in response to external stimuli. Exploring and understanding the stimuli response behavior of flexible MOFs is challenging, as it involves weak host-guest interaction. We report here the unique flexibility of MOF Zn(int)(Ad) (TIF-A1, Hint = isonicotinic acid, Had = adenine) induced by acetylene adsorption. TIF-A1 is rigid toward most gas molecules, while only C₂H₂ can induce the flexibility of TIF-A1. C₂H₂-loaded TIF-A1 is characterized by single-crystal X-ray diffraction and molecular modeling. It is revealed that the flexibility of TIF-A1 originates from the strong interaction between acetylene and the framework, which pushes the rotation of the int ligand and the expansion of the framework simultaneously. This work is helpful in deeply understanding the flexibility of MOFs and guides exploring new flexible MOFs in the future.

Design and synthesis of multifunctional metal-organic zeolites

Metal-organic zeolites (MOZs) are an important branch of metal-organic frameworks (MOFs) and combine the advantages of zeolites and MOFs, such as high surface area and porosity as well as the exceptional stability of zeolites, which would have a significant impact on catalysis chemistry, inorganic chemistry, coordination chemistry, materials science and other areas. In this review, we focus on the recent advances in MOZs with a brief outline of the most prominent examples. In particular, we highlight the basic principles of the design and synthesis approaches toward the construction of MOZs. Obeying the principle of charge matching, tuning tetrahedral metal centers, using enlarged tetrahedral building units as clusters, introducing functional groups into ligands, and combining traditional inorganic TO₄ sites in MOZs enable the final materials with diverse topological structures to exhibit superior performance for various applications, such as gas sorption/separation, catalysis, enantio-selectivity, luminescence, etc.