Ligand
exchange has been widely used to synthesize novel thiolated
gold nanoclusters and to regulate their specific properties. Herein,
density functional theory (DFT) calculations were conducted to investigate
the kinetic profiles of the ligand exchange of the [Au23(SCy)16]− nanocluster with an aromatic
thiolate (2-napthalenethiol). The three types of staple motifs (i.e.,
trimetallic Au3S4, monometallic AuS2, and the bridging thiolates) of the Au23 cluster precursor
could be categorized into eight groups of S sites with different chemical
environments. The ligand exchange of all of them occurs favorably
via the SN1-like pathway, with one site starting with the
Au–S dissociation and seven other sites starting with the H-transfer
steps. By contrast, the SN2-like pathway (i.e., the synergistic
SCy-to-SAr exchange prior to the H-transfer
step) is unlikely in the target systems. Meanwhile, the Au–S
bond on the capping Au atom of the bicapped icosahedral Au15 core is the most active one, while the S sites on Au3S4 (except for the one remote from the metallic core)
are all competitive exchanging sites. The ligand exchange activity
of the bridging thiolate and the remote S site on Au3S4 is significantly less reactive. The calculation results correlate
with the multiple ligand exchange within only a few minutes and the
preferential etching of the AuS2 staple with the foreign
ligands reported in earlier experiments. The relative activity of
different staples might be helpful in elucidating the inherent principles
in the ligand exchange-induced size-evolution of metal nanoclusters.