Hybrid Zeolitic Imidazolate Frameworks with Catalytically Active TO4 Building Blocks

Abstract

Crystalline porous materials with diverse chemical compositions (e.g., inorganic porous materials, inorganic–organic hybrid frameworks, and covalent organic frameworks) and framework topologies have been intensively studied in the past 60 years. They have wide applications in fields such as heterogeneous catalysis, gas storage, and separation. Moreover, some currently emerging areas related to health, energy use, and environmental conservation and remediation are still looking for the development of new porous materials. Zeolites are among the most well known porous materials because of their typical 4-connected open frameworks with TO4 (T= Si , Al, or P etc.) building blocks and outstanding catalytic or gas separation properties. Recently, the search for new zeolite-like structures was extended to metal–organic frameworks (MOFs), and these explorations in part produced a variety of zeolitic imidazolate frameworks (ZIFs) in which the tetrahedrally coordinated divalent cations (M=Zn or Co) are connected by the uninegative imidazolate ligands (im ). The rich chemistry associated with the organic imidazolate building blocks in ZIFs leads to some exceptional properties, such as large surface area and high gas uptake capacities. A question that emerges is: “Are there material with properties intermediate of those of zeolites and ZIFs?”. It is true that there is a hybrid state that remains unknown to date. In this work, we were seeking to integrate compositional and structural features of zeolites and ZIFs by combining TO4 tetrahedra with zinc–imidazolate units. Such a combination is trusted to bear both merits of zeolites and ZIFs, for example, possession of catalytic active TO4 sits of zeolites and high porosity of ZIFs. Herein, we report this kind of hybrid zeolitic imidazolate framework [denoted HZIFs; general formula: M4(im)6TO4] with catalytically active TO4 (T=Mo 6+ or W) building blocks and high thermal stability (up to 550 8C), which presents a new class of porous materials filling the gap between zeolites and ZIFs. The HZIFs reported herein are constructed from two kinds of tetrahedral building blocks and contain two kinds of connectivity, and combine structural features of both zeolites and ZIFs (Scheme 1). The TO4 units used in HZIFs are not traditional SiO4 or AlO4 units in aluminosilicate zeolites, but