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 Cu 2 (COO) 4 cluster in Cu 2 (TCA) 4/3 (H 3 TCA = 4,4′,4″-tricarboxytriphenylamine) framework into a Y 4 (μ 3 –OH) 4 Cu 2 (COO) 12 heterometallic cluster through the introduction of Y 3+ 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 CuO 4 sites, and preserves the spatial arrangement of all TCA linkers with minimal lattice perturbation. The resulting framework, CCNUF-51, adopts a (3,8)-connected the topology arising from merging two adjacent 4-connected paddlewheel nodes of the parent pto net into a single 8-connected node. CCNUF-51 exhibits good chemical stability (pH 2–12), attributed to the synergistic coordination of hard Y 3+ and soft Cu 2+ within the heterometallic SBU. The atomically dispersed Cu sites are intimately coupled to photoactive TCA linkers, enabling highly efficient photocatalytic benzylic C(sp 3 )–H functionalization─including esterification, sulfonamidation, and methoxylation─that outperforms CuI, Cu(OAc) 2, Cu 2 (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.