In Situ Metal Chelation for Topology Regulation and Single‐Site Construction in Covalent Organic Frameworks

Precise regulation over the dimensionality and topology of covalent organic frameworks (COFs) through metal coordination remains a fundamental challenge. Herein, we report an in situ metal‐chelation strategy for topology regulation and single‐site construction in COFs using a bifunctional β ‐hydroxy ketone‐functionalized HDBC monomer. Metal‐free Schiff‐base condensation of HDBC with TAPy affords a one‐dimensional covalent ribbon framework, named COF‐HDBC. Strikingly, in situ Cu 2+ chelation during solvothermal crystallization redirects the assembly pathway toward a two‐dimensional bex ‐type Cu‐COF‐HDBC containing framework‐embedded Cu─O coordination sites. Post‐synthetic metalation of preassembled COF‐HDBC fails to trigger this transformation, verifying the indispensable structure‐directing effect of in situ chelation during nucleation and growth. This strategy is extendable to Ni 2+ and Co 2+ , affording isostructural metal‐chelated COFs. Multiscale characterizations and Cu K‐edge XAFS collectively support the proposed framework structures and the predominantly isolated nature of the Cu centers. As a functional validation, Cu‐COF‐HDBC enables selective CO 2 /CO electroreduction to CH 4 . This work establishes in situ metal chelation as a synthetic handle for programming COF topology and constructing framework‐embedded single‐metal sites, offering a versatile route to crystalline porous materials with complex architectures and tunable functions.