Synthesis, Structure and Light‐Driven H2 Production of a {Ti21} Titanium‐Oxo Cluster Featuring Pentagonal {Ti(Ti5)} Motifs

Abstract Pentagonal {Ti(Ti 5 )} motifs play a crucial role during the assembly of novel titanium‐oxide clusters (TOCs), whose development is still in its infancy. In this work, an unprecedented TOC [(CH 3 ) 2 NH 2 ] 2 [Ti 21 O 29 (O i Pr) 12 (DMF) 6 (SO 4 ) 8 ] ({Ti 21 }) based on {Ti(Ti 5 )} motifs had been obtained under hydrothermal conditions. It possesses ‘fused’ dimeric {Ti 11 } as well as trimeric {Ti 12 } subunits featuring unexpected bonding modes based on pentagonal {Ti(Ti 5 )} motifs. Furthermore, {Ti 21 } exhibits good water and solvent tolerance. As an atomically precise TOCs‐based semiconductor photocatalyst, {Ti 21 } exhibits appreciable photocatalytic hydrogen evolution activity with an optimal hydrogen generation rate of 191.94 μmol/g/h under UV/Vis light. This work provides significant advances and favorable models for the further synthesis of TOCs with unique structure and functionality.