Ag⁺-Mediated Structural Reconstruction of a Metastable Cu₃₅ Cluster Toward Cu-Ag Heterometallic Architectures for...

Controlled structural transformations of metal nanoclusters (NCs) via dynamic bond reorganization provide fundamental insights into cluster reactivity and open avenues for functionality tuning. Here, we report a thiacalix[4]arene-protected Cu(I)-alkynide cluster, {NaCu₃₅(TC4A)₄(Ph-C≡C)₂₀} (Cu₃₅), which exhibits remarkable structural plasticity. This metastable cluster can grow into a Cu₃₆ species via ion substitution or undergo thermal-induced fragmentation to form a smaller Cu₁₄ cluster. Under thermal etching by Ag⁺ ion, structural reconstruction is triggered, leading to the formation of the bimetallic Cu₁₄Ag₆ and Cu₄₀Ag₁₆ clusters. The structural reorganization significantly alters the catalytic outcomes in electrocatalytic CO₂ reduction. Although the monometallic Cu₃₅ and Cu₁₄ favor gaseous CH₄/C₂H₄ production, the bimetallic Cu₁₄Ag₆ demonstrates remarkable selectivity for ethanol synthesis. Notably, Cu₁₄Ag₆ achieves an impressive Faradaic efficiency (FE) of 49.27% for ethanol production, alongside a high partial current density of -67.94 mA cm^-2. This marks the highest ethanol selectivity reported to date for atomically precise cluster catalysts. Mechanistic investigations reveal that, compared to homometallic Cu⋯Cu dual sites (which typically favor C₂H₄), the unique Ag⋯Cu⋯Cu trimetallic microstructure in Cu₁₄Ag₆ is more thermodynamically favorable for asymmetric C─C coupling between *CHO and *OCH₂, facilitating the formation of the key *CHO-*OCH₂ intermediate, which drives the ethanol-selective pathway.