Enhancing stability through ligand-shell engineering: A case study with Au25(SR)18 nanoclusters

Abstract

While thiolate-protected Au nanoclusters (NCs) have drawn considerable interest in various fields, their poor stability in aqueous solution remains a major hurdle for practical applications. Here, we report a unique strategy based on ligand-shell engineering to improve the stability of thiolated Au NCs in solution. By employing two thiol-terminated ligands having oppositely charged functional groups on the surface of the NCs, we demonstrate that the electrostatic attraction between the oppositely charged functional groups of neighboring ligands could amplify the coordination among surface ligands, leading to the formation of pseudo-cage-like structures on the NC surface that could offer higher protection to the Au core in aqueous solution. The strategy developed in this study could be extended to other metal NCs, further paving the way toward practical applications.

Charge Neutralization Strategy: A Novel Synthetic Approach to Fully Cationized Thiolate‐Protected Au25(SR+)18 Clusters with Atomic Precision

“…The reduced decomposition temperature observed in Figure may indicate the lower stability of fully cationized Au clusters. A similar phenomenon was also reported in anionic charged Au 25 (mercaptocarboxylic acid) 18 clusters, where shorter alkyl chain lengths drastically decreased the thermal stability of a cluster in solution due to the shorter distance between the charges . Densely populated cationic groups on the surface of Au 25 clusters probably reduce the thermal stability in our case.…”

“…Under such heterogeneous conditions, homogeneous reduction and growth of the Au clusters is expected to be highly restricted. Moreover, Coulombic repulsion between densely populated cationic charges on the cluster surfaces may decrease the thermal stability, as similarly reported for anionic Au 25 (mercaptocarboxylic acid) 18 clusters with different chain lengths . Due to the considerations outlined above, the synthesis of cationic thiolate‐protected Au clusters has been highly limited.…”

Thermodynamic stability of ligand-protected metal nanoclusters

“…Toward understanding ligand impact we highlight that experimentally41 and theoretically42, the [Au 25 SR 18 ] − NC has been shown to be stable for a wide variety of ligands, and was successfully synthesized even with small, ethyl R groups43. Therefore, the exceptional structural stability of [Au 25 SR 18 ] − NC seems to be experimentally independent of the ligand type, highlighting the importance of metal structure and AuS −1 stoichiometry in determining stable NCs.…”

Practical stability of Au25(SR)18−1/0/+1

“…6–8 This is an area that has been well studied for larger colloidal particles 9–12 , but it is not clear whether the same principles apply to the smaller particles, and how colloidal descriptions of stability and superatomic descriptions of stability interact.…”

“…17,20 For water soluble nanoclusters, manipulation of ligand shell charge has been shown to improve solution stability. 8,21 …”