Ligand Exchange on Au38(SR)24: Substituent Site Effects of Aromatic Thiols
Understanding the critical roles of ligands (e.g. thiolate, SR) in forming metal nanoclusters of specific sizes has long been an intriguing task since the report of ligand-exchange-induced transformation of Au38(SR)24 to Au36(SR’)24. Herein, we conduct a systematic study of ligand exchange on Au38(SC2H4Ph)24 with 21 incoming thiols and reveal that the size/structure preference is dependent on the substituent site. Specifically, ortho-substituted benzenethiols preserve the structure of Au38(SR)24, while para- or non-substituted benzenethiols cause the transformation to Au36(SR)24. Strong electron donating or withdrawing groups do not make a difference, but will inhibit full ligand exchange. Moreover, the crystal structure of Au38(SR)24 (SR = 2,4-methylbenzenthiolate) exhibits distinctive π•••π stacking as well as “anagostic” interaction (indicated by substantially short Au•••H distances). Theoretical calculations find the raised energies of frontier orbitals for aromatic ligand-protected Au38, indicating decreased electronic stability. However, this adverse effect could be compensated by the Au•••H-C interactions which improve the geometric stability when ortho-substituted benzenethiols are used. Overall, this work reveals the substituenet site effect based on the Au38 model, and stresses the long-neglected “anagostic” interactions on the surface of Au-SR NCs which improves the structural stability.
- This article is part of the themed collection: 2020 Nanoscale HOT Article Collection