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(^iPrNHC^iPr)(PhC≡C)₄ (Au₃Cu, where ^iPrNHC^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 Au₃Ag(^iPrNHC^iPr)(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(^iPrNHC^iPr)(PhC≡C)₄]₂ (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.