Geometry-Controlled Synergy of Adjacent Cu(I) Sites Enhances C-C Coupling for Efficient CO₂-to-C₂₊ Electroreduction

The electrochemical reduction of CO₂ to multicarbon (C₂₊) products offers a promising route to sustainable fuels and chemicals, while controlling the critical C-C coupling step remains a fundamental challenge. Here, we demonstrate that engineering the molecular geometry of Cu(I) sites in crystalline Cu-triazine frameworks directly tunes the selectivity of CO₂RR. Two structurally well-defined copper frameworks, the Cu₃I₃-triazine and Cu₂I₂-triazine with different Cu-I-Cu bridge geometries, are employed as catalysts for CO₂ electroreduction. The Cu₂I₂-triazine catalysts achieved a high Faradaic efficiency of 73.7% for C₂₊ products at a current density of -300 mA cm^-2, significantly outperforming the Cu₃I₃-triazine counterpart in CO₂ electroreduction. Through a combination of in situ spectroscopy and density functional theory calculations, we elucidate that the adjacent Cu(I) sites in Cu₂I₂-triazine catalyst facilitate interfacial water dissociation for the stabilization of critical *CHO intermediates, and steer the C-C coupling pathway for efficient C₂₊ formation. This work establishes a direct link between molecular-scale spatial symmetry of molecular catalysts and their catalytic synergy for C₂₊ products in CO₂RR.