Metallosalphen-Based 2D Covalent Organic Frameworks with an Unprecedented tju Topology via K-Shaped Two-in-One Monomers

Increasing research interest has been raised in two-dimensional covalent organic frameworks (2D COFs) probably due to their intriguing structural features and versatile functions. However, due to the relatively limited configuration of precursors, the documented 2D COFs to date have been limited to only nine topologies which greatly restricts their development. Herein, we newly designed and synthesized three K-shaped “two-in-one” building units (Ni-Salphen, Cu-Salphen, and Zn-Salphen), which not only feature a special configuration distinguished from the reported monomers but also integrate metallosalphen functional moieties. Self-polycondensation of these K-shaped monomers facilely afforded three new metallosalphen-based COFs (Ni-Salphen-COF, Cu-Salphen-COF, and Zn-Salphen-COF) with an unprecedented tju topology (tju = Tianjin University) that does not exist in the database of ToposPro. Regarding to the densely and uniformly distributed metallosalphens in the skeletons, the photocatalytic bromination performance of the three COFs were further investigated. Among them, Ni-Salphen-COF exhibited the highest performance on both conversion efficiency (>99%) and selectivity (>90%).