Oxygen insertion at the cage center: an unconventional tuning strategy for enhancing the photocatalytic performance of atomically precise copper cluster cocatalysts

To fully comprehend the correlation between the structure and photocatalytic performance of copper clusters, an atomically precise model is imperative. Nevertheless, the challenge of precisely controlling the electronic structure of these clusters persists. Herein, by accurately manipulating experimental conditions, three fourteen-nuclear thiolate copper clusters of [Cu14(SCPh)12(P(Ph-F)3)6](NO3)2 (Cu14) [Cu14(mu 6-O)(SCPh)12(P(Ph-F)3)6] (O@Cu14) and [Cu14(SCPh)12(P(Ph-F)3)6][Cu14(mu 8-O)(SCPh)12(P(Ph-F)3)6](NO3)2 ([Cu14][O@Cu14]), are demonstrated. Especially in O@Cu14 and [Cu14][O@Cu14], the subunit of the Cu8 cage center facilitates the insertion of a central oxygen atom. Although researchers have predicted that the Cu8 cage center can accommodate a central oxygen atom, to date, there have been no reports of copper clusters with such sub-structural units. Moreover, the impact of central oxygen atom insertion, particularly on the catalytic performance of copper clusters, remains an unresolved issue. When these copper clusters are loaded onto the surface of hydroxyl-functionalized g-C3N4 nanosheets (g-C3N4(OH)), the resulting composites exhibit excellent H2-production performance compared to that of g-C3N4(OH). Moreover, the significantly enhanced catalytic activity of O@Cu14@g-C3N4(OH) compared to Cu14@g-C3N4(OH) demonstrates that the insertion of oxygen atoms in the Cu8 cage can markedly affect the electronic structure of copper clusters, thereby enhancing the photocatalytic activity. In the case of [Cu14][O@Cu14]@g-C3N4(OH), the matching effect between two copper clusters' HOMO-LUMO energy levels additionally enhances the photocatalytic activity, leading to a value-added effect. This study not only confirms the long-standing prediction that the Cu8 center can accommodate an oxygen atom but also demonstrates a novel central atom regulation strategy to obtain highly active copper clusters as photocatalysts. This work not only confirms the long-standing prediction that the Cu8 center can accommodate an oxygen atom but also demonstrates a novel central atom regulation strategy to obtain highly active copper clusters as photocatalysts.