Embedding Cu ₄ X ₄ Cubane Clusters into Lead Halide Lattices: Stable 3D Cu‐Pb Bimetallic Halide Frameworks for Photocatalytic CO ₂ ‐to‐Ethylene Conversion in Water

Abstract 3D hybrid lead halides have emerged as promising photofunctional materials; however, the 3D structural prototypes remain scarce due to the stringent requirements for organic cations to fit within the framework cavities and stabilize PbX 6 networks. Moreover, their ionic‐bound nature and highly symmetric PbX 6 units often result in structural instability and suppressed C─C coupling capabilities, posing significant challenges for photocatalytic CO 2 ‐to‐C 2+ conversion in aqueous environments. Herein, a heterometallic crystal engineering strategy is presented for the coordination‐driven assembly of two 3D M I /M II bimetallic halides with the general formula Pb 6 Cu 4 X 10 (ida) 3 (ida = iminodiacetate, X = Cl − /Br − ). The embedding of cubane‐type [Cu 4 X 4 ] clusters within the lead halide frameworks via covalent Pb II –X–Cu I linkages result in decreased exciton binding energies, smaller Huang–Rhys factors, and extended photoluminescence lifetimes, which suppress exciton trapping and facilitate carrier transport. Both M I /M II halide frameworks feature asymmetric, halogen‐bridged heterobimetallic sites (Pb II ─X─Cu I ) with intrinsic charge polarization, which facilitate C─C coupling during CO 2 photoreduction by stabilizing the key *COCOH intermediates. As a result, these heterobimetallic architectures enable highly selective photocatalytic CO 2 ‐to‐C 2 H 4 conversion, achieving up to 95% selectivity in pure water. This work demonstrates a viable strategy for atomic‐level engineering of 3D metal halides toward solar‐driven C 2 fuel production.