Reticular Synthesis of 3D Metal Cluster-Based COFs With Record High-Connectivity for Efficient Photocatalytic H2O2 Synthesis.

The assembly of metal clusters with organic building units by covalent bonds to form metal cluster-based covalent-organic frameworks (MCCOFs) material is a novel strategy in reticular synthesis. However, only 2, 3, and 6 connectivity of MCCOFs have been achieved in reported structures. Developing a higher connectivity remains a great challenge in the MCCOFs due to the difficulties in introducing multiple connecting nodes to the metal cluster. In this work, two 3D [8 + 2]-connected MCCOFs were synthesized by condensing an 8-connectivity aluminum cluster-based building block (termed Al8-8c) with linear dialdehyde linkers. Furthermore, these AlCCOFs showed efficient photocatalytic O2-to-H2O2 conversion due to the suitable energy band structure, efficient photoelectron conversion capability and the AlCCOF-1 showed H2O2 photosynthetic efficiency of 16794.69 µmol g-1 h-1 using water and benzyl alcohol reaction system. The in situ EPR, in situ FTIR, and DFT calculations were then performed to study the structure-function relationships on the two AlCCOFs for H2O2 photosynthesis. This work is the first report of high-connectivity MCCOFs bearing 8-connected cluster units, showing the great potential of using metal clusters to construct complicate reticular frameworks by covalent linkage.