[N⋯Br⋯N]⁺ Type Halogen Bonding: From Structure to Applications

Noncovalent halogen bonding, particularly the three-center four-electron (3c-4e^-) [N⋯X⋯N]⁺ motif, represents a critical tool in supramolecular chemistry and materials science. While I⁺-based systems are well-studied, this review focuses on the emerging and highly functional [N⋯Br⋯N]⁺ motif and its application in halogen-bonded organic frameworks (XOFs). The authors comprehensively summarize the synthetic strategies required to overcome the instability of the Br⁺ species, including halogen bond network spatial constraint, cation substitution, ligand exchange, and precise anionic regulation. Structural analysis reveals that the shorter N⋯Br bond length (2.07 Å) and stronger electron-deficient characteristics of the Br⁺-bridge provide unique functional advantages. This structural superiority translates to enhanced performance in applications such as selective alcohol oxidation and highly efficient photocatalytic H₂O₂ production, where XOFs(Br) materials consistently outperform their I-analogues and molecular precursors. Furthermore, it also highlights the potential of XOFs(Br) in biomedical fields, including superior antimicrobial activity and applications in photothermal therapy. This work confirms the significant potential of the [N⋯Br⋯N]⁺ motif to drive future innovation in controllable functional materials, paving the way for the design of stable Br⁺-bridged XOFs for catalysis, precision medicine, and others.