Regulation of Coordinating Anions around Single Co(II) Sites in a Covalent Organic Framework for Boosting CO2 Photoreduction

While photocatalytic CO₂ reduction has been intensively investigated, reports on the influence of anions coordinated to catalytic metal sites on CO₂ photoreduction remain limited. Herein, different coordinated anions (F^–, Cl^–, OAc^–, and NO₃^–) around single Co sites installed on bipyridine-based three-component covalent organic frameworks (COFs) were synthesized, affording TBD-COF-Co-X (X = F, Cl, OAc, and NO₃), for photocatalytic CO₂ reduction. Notably, the presence of these coordinated anions on the Co sites significantly influences the photocatalytic performance, where TBD-COF-Co-F exhibits superior activity to its counterparts. Combined experimental and theoretical results indicate that the enhanced activity in TBD-COF-Co-F is attributed to its efficient charge transfer, high CO₂ adsorption capacity, and low energy barrier for CO₂ activation. This study provides a new strategy for boosting COF photocatalysis through coordinated anion regulation around catalytic metal sites.