One Atom Makes a Big Difference in NHC‐Ligated Alloy Nanoclusters: From Structure and Properties to Catalysis

ABSTRACT Despite active research on N‐heterocyclic carbene (NHC)‐protected metal nanoclusters, their development faces challenges due to limited structural and property control. Especially, the precise manipulation of structure and property of NHC‐ligated alloy nanoclusters remains unexplored. Here, we present an atomistic‐level model system demonstrating single‐atom control in NHC‐stabilized alloy nanoclusters. By varying a single copper atom with silver in Au 3 Cu( iPr NHC iPr )(PhC≡C) 4 (Au 3 Cu, where iPr NHC iPr is a bidentate NHC ligand and PhC≡C is phenylacetylide), we reveal how one atomic change dramatically alters the structure, properties, and catalytic behavior of these clusters. The newly synthesized Au 3 Ag( iPr NHC iPr )(PhC≡C) 4 retains a tetrahedral metal framework and surface coordination pattern similar to Au 3 Cu, yet the single‐atom variation (Ag for Cu) triggers profound differences. Notably, while Au 3 Cu exists as a monomer, the Au 3 Ag clusters spontaneously dimerize, forming [Au 3 Ag( iPr NHC iPr )(PhC≡C) 4 ] 2 (denoted as (Au 3 Ag) 2 ). Single‐cluster junction conductance measurements reveal a colossal conductance difference of up to 30‐fold of magnitude between the two systems. Furthermore, the (Au 3 Ag) 2 dimer exhibits exceptional catalytic selectivity in electrocatalytic CO 2 reduction, achieving a CO Faradaic efficiency of 70%—more than double that of the Au 3 Cu monomer. Density functional theory calculations and experimental data elucidate the origin of these dramatic structural and functional disparities induced by a single‐atom change.