Metal‐Organic Cages Assembled From {Ni ₆ } Nodes for Selective CO ₂ Reduction

Abstract

Abstract Constructing cluster‐based nodes and using them as catalytic sites can bring new structure and function for metal‐organic cages (MOCs). However, successful examples are very limited. Herein, we found that a 2‐mercapto‐5‐methyl‐1,3,4‐thiadiazole (Hmmt) based {Ni 6 } subunit is robust in building such MOCs. The {Ni 6 } node is based on the central Ni 4 cubane and two wing Ni(II) ions with virtually three or four connected features. When various carboxylate ligands are incorporated the triangular prismatic [Ni 18 (Hmmt) 3 (mmt) 12 (BPDC) 6 (CH 3 O) 12 (H 2 O) 6 (DMF) 6 ] ( 4 /MOC‐18N, H 2 BPDC = biphenyl‐4,4′‐dicarboxylic acid), tetrahedral‐like [Ni 24 (Hmmt) 4 (mmt) 16 (BTC) 4 (CH 3 O) 16 Cl 4 (H 2 O) 4 (DMF) 5 (CH 3 OH) 3 ] ( 5 /MOC‐24N, H 3 BTC = 1,3,5‐benzenetricarboxylic acid) and the octahedral [Ni 36 (Hmmt) 6 (mmt) 24 (BTC) 8 (CH 3 O) 24 (H 2 O) 12 (DMF) 12 ] ( 6 /MOC‐36N) can be isolated. Interestingly, MOCs 4–6 can uptake CO 2 in solid states. Moreover, they can effectively and selectively convert CO 2 into CO under visible light owing to the active wing Ni(II) ions, which are ancillarily coordinated with solvent molecules. All of them show turnover frequencies larger than 3500 µmol·g −1 ·h −1 and selectivity higher than 90%. This is a much higher performance compared to the usage of cage space for CO 2 reduction in previously reported MOCs and competitive to most Ni(II)‐based simple coordination complexes. As such, this work may open a new paradigm for designing node based catalytic function for MOCs.