Face-Sharing Archimedean Solids Stacking for the Construction of Mixed-Ligand Metal-Organic Frameworks

Reticular chemistry has been an important guiding principle for the design of metal-organic frameworks (MOFs). This approach utilizes discrete building units (molecules and clusters) that are connected through strong bonds into extended networks assisted by topological considerations. Although the simple design principle of connecting points and lines has proved successful, new design strategies are still needed to further explore the structures and functions of MOFs. Herein, we report the design and synthesis of two mixed-ligand MOFs, [(CH₃)₂NH₂]₄[Zn₄O]₄[Zn(TCPP)]₅[BTB]_8/3 (PCN-137) and [Zr₆(μ₃-O)₄(μ₃-OH)₄][TCPP][TBTB]_8/3 (PCN-138) (BTB = 1,3,5-benzene(tris)benzoate, TBTB = 4,4',4″-(2,4,6-trimethylbenzene-1,3,5-triyl)tribenzoate, and TCPP = tetrakis(4-carboxyphenyl)porphyrin) by the stacking of face-sharing Archimedean solids. In these two MOFs, high-symmetrical metal clusters serve as vertices, and tritopic or tetratopic carboxylate ligands function as triangular and square faces, leading to the formation of two kinds of Archimedean solids (rhombicuboctahedron and cuboctahedron). Furthermore, the ordered accumulation of Archimedean solids successfully gives rise to 3D structures through face-sharing, highlighting the polyhedron-based approach for the design and preparation of MOFs. In addition, PCN-138 was utilized as a heterogeneous catalyst toward CO₂ photoreduction under visible-light irradiation. This structure shows high photocatalytic activity, which can be attributed to the coexistence of photosensitizing porphyrin fragments and Zr-oxo centers within the PCN-138 scaffold.