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

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 Au3Cu(iPrNHCiPr)(PhC≡C)4 (Au3Cu, where iPrNHCiPr 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 Au3Ag(iPrNHCiPr)(PhC≡C)4 retains a tetrahedral metal framework and surface coordination pattern similar to Au3Cu, yet the single-atom variation (Ag for Cu) triggers profound differences. Notably, while Au3Cu exists as a monomer, the Au3Ag clusters spontaneously dimerize, forming Au3Ag(iPrNHCiPr)(PhC≡C)42 (denoted as (Au3Ag)2). Single-cluster junction conductance measurements reveal a colossal conductance difference of up to 30-fold of magnitude between the two systems. Furthermore, the (Au3Ag)2 dimer exhibits exceptional catalytic selectivity in electrocatalytic CO2 reduction, achieving a CO Faradaic efficiency of 70%-more than double that of the Au3Cu monomer. Density functional theory calculations and experimental data elucidate the origin of these dramatic structural and functional disparities induced by a single-atom change.