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Beyond Traditional Four-Connected Zeolitic Frameworks: Design, Syntheses and Characterization of Porous Zeolitic Imidazolate Frameworks and Open-Framework Metal Chalcogenides

  • Author(s): Wu, Tao
  • Advisor(s): Feng, Pingyun
  • et al.
Abstract

Zeolites have played essential roles in a number of industrial processes and technological applications. The intensive research in crystalline microporous materials has successfully extended such traditional inorganic zeolites to semiconducting open-framework metal chalcogenides and hybrid porous coordination polymers. Our research group has made a number of key advances in the development of metal chalcogenide clusters and their self-assembled open frameworks. Some of these key advances resulted from this thesis work and are described here. This dissertation also deals with the synthesis of some unique families of porous frameworks based on coordination polymers.

Porous zeolitic metal imidazolate frameworks can be considered as integrating features of both traditional inorganic zeolites and porous coordination polymers because the Si-O-Si angle in zeolites is coincident with that of the bridging angle formed by the Metal-Imidazolate-Metal unit. In this thesis work, two different strategies are employed. The first is the use of mixed, sterically tuned and complementary imidazole ligands, which results in several novel zeolitic topologies with both 3-ring and large rings (>12). The second is the use of novel tetrahedral nodes (e.g., Li and B), which leads to a new family of boron imidazolate open-framework materials.

Open-framework metal chalcogenides are a new generation of inorganic porous materials because their semiconducting properties could expand the utility of inorganic porous materials into areas in which traditional insulating inorganic zeolite materials have had little impact. Key synthetic discoveries made in this thesis work include (1) synthesis of a family of Sn- and/or S-doped Zn-Ga-Se clusters and frameworks and demonstration of site-selective doping chemistry controlled by the interplay of multiple fundamental chemical and geometrical factors, (2) synthesis of two selenide 3D superlattices based on dual-sized supertetrahedral clusters and demonstration of charge density tuning of chalcogenide clusters using three types of charge-complementary and yet geometry-matching metal cations (di-, tri-, and tetravalent ions), (3) synthesis of the largest discrete chalcogenide clusters with tunable band gaps, which further blurs the boundary between molecular clusters and colloidal nanoparticles, and (4) the synthesis of a new family of 3D covalent arrays of supertetrahedral clusters and negatively-charged imidazolate ligands.

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