Metal Nanoparticles Confronted with Foreign Ligands: Mere Ligand Exchange or Further Structural Transformation?

Ligand exchange reactions have attracted extensive interest due to their utility in tailoring the properties and applications of metal nanoparticles, but these techniques are not well understood due to the unclearness of metal nanoparticles at an atomic level. The emerging ultrasmall metal nanoparticles (metal nanoclusters) provide excellent opportunities for investigating this challenging issue. Herein, it is revealed that structurally similar Au-25(SC2H4Ph)(18), Au24Cd(SC2H4Ph)(18,)and Au24Hg(SC2H4Ph)(18)transform to Au-24(SCH2Ph-Bu-t)(20), Au24Cd(SCH2Ph-Bu-t)(18)and approximate to 5 nm gold nanoparticles after reacting with HSCH2Ph-Bu-t, respectively. Based on this and some other facts, it is suggested that the intrinsic stability is one key factor that determines the ligand exchange direction, whether by mere ligand exchange or further structure transformation (including aggregation). Single crystal X-ray crystallography further reveals that the partial surface ligand configuration reverses after ligand exchange, providing structure evidence for the unimolecular nucleophilic substitution (S(N)1)-like mechanism.

Automated summary

Ligand exchange reactions in metal nanoparticles, especially metal nanoclusters, have attracted significant interest for tailoring their properties. The intrinsic stability plays a key role in determining the direction of ligand exchange, as revealed by single crystal X-ray crystallography. The reversal of surface ligand configuration after exchange provides evidence for a unimolecular nucleophilic substitution mechanism.