Unraveling Bonding Evolution in Carbon-Centered Gold(I) Clusters: Structural, Electronic, and Ligand Effects

Despite recent advances in the synthesis and structural characterization of carbon-centered gold(I) clusters, the fundamental nature of their C−Au bonding and its relationship with the number of Au atoms remain elusive. Here, we report a comprehensive theoretical investigation of CAuIn (n = 6, 5, 4) clusters protected by N-heterocyclic carbene and triphenylphosphine ligands, revealing a systematic evolution of the bonding architecture. Using adaptive natural density partitioning analysis, we identified the transition from classical two-center two-electron (2c−2e) C−Au bonds in the CAu4 core to delocalized three-center two-electron (3c−2e) Au−C−Au bonds specific to the CAu6 core. Notably, the CAuI5 cluster acts as a structural bridge, featuring two axial 2c−2e bonds with orbital characteristics resembling those of the 3c−2e bonds in CAuI6, together with three equatorial 2c−2e bonding environments. This study demonstrates that the relative contributions of the central carbon 2s and 2p orbitals serve as a key electronic descriptor of the nature of C−Au bonding. Furthermore, the coordinated ligands influence the structural distortion of the CAu6 core. Smaller ligands tend to favor symmetric CAu6 cores, whereas bulkier ligands are associated with greater core distortion and a preference for asymmetric CAu6 cores. Both the distortion of the CAu6 core and the chiral ligands contribute to the chirality of the entire metal cluster. This study provides an integrated bonding model that correlates the number of Au atoms in the cluster, electronic structure, ligand effects, stability, and chirality, offering valuable insights for the rational design of functionalized gold(I) nanoclusters.