Design and Characterization of Porphyrinic Metal-Oragnic Frameworks

Abstract

Metal-Organic Frameworks (MOFs) have been a main theme in materials chemistry for the past two decades because of their potential applications such as catalysis and gas storage. Many MOFs are porous materials consisting of metal clusters and organic linkers through coordination bond with large pore. Despite of such advantages, synthesis of MOFs with unsaturated metal sites has been a daunting challenge. Thus, many research groups have been interested in metalloligand. Especially, we have been interested in the porphyrin linker to be used as a building block for MOF synthesis. Extended porphyrin linker and various SBU make more complicated structure. The resulting structures can be simplified using polyhedra such as Platonic and Archimedean solids. New Expandable Porphyrin-MOF (EP-MOF), assembled from 5, 10, 15, 20-tetrakis [3-carboxyphenyl] porphyrin (3-TCPP) ligand and three blade paddlewheel SBU (Zn2(COO)3+), is an important flexible MOF with rhombicuboctahedron as a basic structure building unit. Overall topology of this MOF can be considered as body-centered cubic packing with porphyrinic cubes. Also, the movement of the cubes is expandable upon heating, confirmed by single-crystal x-ray diffraction data. Secondly, PMOF-100 is non-pillared structures based on rhombicuboctahedron packing. The complex was constructed from 5, 10, 15, 20-Tetrakis [3, 5-dicarboxylphenyl] porphyrine (OCPP) ligand and Cu paddlewheel SBU. The upper and bottom caps, which are composed of two porphyrins and paddlewheel, are connected with Cu ions. The Cu ions as bridge are special points of middle sites in a cage. Due to Cu ions of this middle site, PMOF-100 has many unsaturated metal sites when it is activated. This structure has similar to the amount of open metal sites of HKUST-1. Lastly, new 2D porphyrinic MOF, PPF-300, was synthesized via self-assembly of 5, 10, 15, 20-tetrakis [4-carboxymethyleneoxyphenyl] porphyrin (TCMOPP) ligand and Zn paddlewheel SBU. PPF-300 has the potential flexibility due to the linker with substituted functional group unlike rigid 4-TCPP (5, 10, 15, 20-tetrakis [4-carboxyphenyl] porphyrin). A similar structure by Goldberg group is also 2D porphyrinic MOF using TCMOPP linker. PPF-300 can be represented by square-grid and Goldberg’s structure can be simplified to hourglass.