Polyoxometalate-organic cage with {Ni4SiW9} node for photocatalytic hydrogen evolution

The design and syntheses of metal-organic cages (MOCs) based on polyoxometalates (POMs) building blocks have been attracted increasing attention due to their intriguing molecular architectures and physicochemical properties. In this work, we have successfully synthesized and systematically characterized a tetrahedral polyoxometalate-based organic cage (POC), K3Na17H12[(C4H6O6)6[Ni4(OH)3(A-α-SiW9O34)]4]·96H2O (Ni16L6(SiW9)4), using tritopic Ni4-substituted Keggin cluster (Ni4SiW9) as nodes and flexible L-(+)-tartaric acid ligands as linkers. The resulting POC tetrahedron has been firstly investigated as efficient catalyst for visible-light-driven hydrogen production, achieving a turnover number of 15500 after 96-h photocatalysis. Such high catalytic performance of Ni16L6(SiW9)4 POC catalyst could be attributed to its unique cage structure, thereby offering more efficient catalytic component accessibility. In addition, spectroscopic analyses illustrated the photocatalytic mechanism and the structural stability of the TBA-Ni16L6(SiW9)4 catalyst during the photocatalytic process.