Control of single-ligand chemistry on thiolated Au₂₅ nanoclusters

Diverse methods have been developed to tailor the number of metal atoms in metal nanoclusters, but control of surface ligand number at a given cluster size is rare. Here we demonstrate that reversible addition and elimination of a single surface thiolate ligand (-SR) on gold nanoclusters can be realized, opening the door to precision ligand engineering on atomically precise nanoclusters. We find that oxidative etching of [Au₂₅SR₁₈]^- nanoclusters adds an excess thiolate ligand and generates a new species, [Au₂₅SR₁₉]⁰. The addition reaction can be reversed by CO reduction of [Au₂₅SR₁₉]⁰, leading back to [Au₂₅SR₁₈]^- and eliminating precisely one surface ligand. Intriguingly, we show that the ligand shell of Au₂₅ nanoclusters becomes more fragile and rigid after ligand addition. This reversible addition/elimination reaction of a single surface ligand on gold nanoclusters shows potential to precisely control the number of surface ligands and to explore new ligand space at each nuclearity.