All-N-Heterocyclic-Carbene Protected Superatomic Ag₈ Cluster

Atomically precise monolayer-protected coinage metal nanoclusters (CMNCs) have drawn increasing attention for their diverse structures and intriguing properties. Nevertheless, not all-N-heterocyclic-carbene (NHC)-protected atomically precise silver nanoclusters have been synthesized yet. Herein, we report the synthesis and crystal structure of the first all-NHC-protected superatomic silver cluster. This NHC-ligand-stabilized Ag₈ cluster, characterized as Ag₈K₂L₄(CO₃)₂(PF₆)₆, was prepared by reacting Ag₂O with bisimidazolium salt H₂-L(PF₆)₂ under alkaline conditions in dimethylformamide via a one-pot reaction. The results of single-crystal X-ray diffraction analysis, multinuclear nuclear magnetic resonance (NMR) spectroscopy, and high-resolution electrospray-ionization (HR-ESI) mass spectrometry revealed a cluster centered with a stable Ag₈ ring. Energy decomposition analysis combined with the natural orbital for chemical valence method (EDA-NOCV) was employed to analyze the nature of the Ag–ligand bonding, and the results suggested that the stabilization energy originated from the strong electrostatic attraction of the Ag₈ ring to the NHC ligand. This work is expected to enable new applications of various NHC ligands in the formation of NHC-protected metal clusters with attractive properties.