Ag⁺‐Mediated Structural Reconstruction of a Metastable Cu 35 Cluster Toward Cu–Ag Heterometallic Architectures for Superior Electrocatalytic CO 2 ‐to‐Ethanol Conversion

Abstract 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, {NaCu 35 (TC4A) 4 (Ph‐C≡C) 20 } ( Cu 35 ), which exhibits remarkable structural plasticity. This metastable cluster can grow into a Cu 36 species via ion substitution or undergo thermal‐induced fragmentation to form a smaller Cu 14 cluster. Under thermal etching by Ag + ion, structural reconstruction is triggered, leading to the formation of the bimetallic Cu 14 Ag 6 and Cu 40 Ag 16 clusters. The structural reorganization significantly alters the catalytic outcomes in electrocatalytic CO 2 reduction. Although the monometallic Cu 35 and Cu 14 favor gaseous CH 4 /C 2 H 4 production, the bimetallic Cu 14 Ag 6 demonstrates remarkable selectivity for ethanol synthesis. Notably, Cu 14 Ag 6 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 C 2 H 4 ), the unique Ag⋯Cu⋯Cu trimetallic microstructure in Cu 14 Ag 6 is more thermodynamically favorable for asymmetric C─C coupling between *CHO and *OCH 2 , facilitating the formation of the key *CHO−*OCH 2 intermediate, which drives the ethanol‐selective pathway.