A Heterometallic Metal–Organic Framework with Atomically Precise Single-Cu Sites for Photocatalysis

Atomically precise single-atom catalysts (SACs) are essential for establishing reliable structure-activity relationships, yet synthetic routes that afford SACs with fully resolved coordination microenvironments remain a significant challenge. Here we report a secondary building unit (SBU) deconstruction-reorganization strategy that converts the dicopper Cu₂(COO)₄ cluster in Cu₂(TCA)_4/3 (H₃TCA = 4,4',4″-tricarboxytriphenylamine) framework into a Y₄(μ₃-OH)₄Cu₂(COO)₁₂ heterometallic cluster through the introduction of Y³⁺ and 2-fluorobenzoic acid modulator. Single-crystal X-ray diffraction unambiguously captures this reorganization, which expands the Cu···Cu distance from 2.6 to 10.3 Å, generates two isolated square CuO₄ sites, and preserves the spatial arrangement of all TCA linkers with minimal lattice perturbation. The resulting framework, CCNUF-51, adopts a (3,8)-connected <b>the</b> topology arising from merging two adjacent 4-connected paddlewheel nodes of the parent <b>pto</b> net into a single 8-connected node. CCNUF-51 exhibits good chemical stability (pH 2-12), attributed to the synergistic coordination of hard Y³⁺ and soft Cu²⁺ within the heterometallic SBU. The atomically dispersed Cu sites are intimately coupled to photoactive TCA linkers, enabling highly efficient photocatalytic benzylic C(sp³)-H functionalization─including esterification, sulfonamidation, and methoxylation─that outperforms CuI, Cu(OAc)₂, Cu₂(TCA)_4/3, and benchmark Cu/UiO-66 SAC. This work establishes SBU deconstruction-reorganization as an effective route for accessing SACs with atomically well-defined active sites.