Heterocyclic-N-Coordinated Ag₂^δ- Monolayer Self-Assembled on Ag(100)

The charge states of metal adatoms on surfaces play a crucial role in controlling adsorption and interaction behaviors that underpin surface chemistry and catalysis, yet the atomically precise synthesis of negatively charged metal atoms remains a significant challenge. Here, we report negatively charged Ag dimer (Ag₂^δ-) arrays assembled on Ag(100) surface through coordination with a polycyclic aromatic hydrocarbon, 8,9-diaza-8a-borabenzo[fg]tetracene (DBT), featuring a doping moiety with N-B-N bonds at zigzag edge. The Ag dimers are stabilized by two DBT monomers through N-Ag-N coordination bonding. In contrast to surface Ag atoms, the coordinated dimers display anionic character, as demonstrated by noncontact atomic force microscopy, Kelvin probe force microscopy, X-ray photoelectron spectroscopy, and density functional theory calculations. Neutral dimers Ag₂⁰ can be converted from the coordinated complex by tip-induced detachment of one DBT monomer and showed markedly higher affinity for CO adsorption, a process that is suppressed on Ag₂^δ-. These findings establish an atomically defined platform for stabilizing and controlling anionic metal centers on metallic surfaces, providing a model system for exploring charge-state effects in surface chemistry.