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

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 PbX₆ networks. Moreover, their ionic-bound nature and highly symmetric PbX₆ units often result in structural instability and suppressed C─C coupling capabilities, posing significant challenges for photocatalytic CO₂-to-C₂₊ 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 Pb₆Cu₄X₁₀(ida)₃ (ida = iminodiacetate, X = Cl^-/Br^-). The embedding of cubane-type [Cu₄X₄] 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 CO₂ photoreduction by stabilizing the key *COCOH intermediates. As a result, these heterobimetallic architectures enable highly selective photocatalytic CO₂-to-C₂H₄ 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 C₂ fuel production.