Ligand exchange on Au38(SR)24: substituent site effects of aromatic thiols

Understanding the critical roles of ligands (e.g. thiolates, SR) in the formation of metal nanoclusters of specific sizes has long been an intriguing task since the report of ligand exchange-induced transformation of Au-38(SR)(24) into Au-36(SR ')(24). Herein, we conduct a systematic study of ligand exchange on Au-38(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 Au-38(SR)(24), while para- or non-substituted benzenethiols cause its transformation into Au-36(SR)(24). Strong electron-donating or -withdrawing groups do not make a difference, but they will inhibit full ligand exchange. Moreover, the crystal structure of Au-38(SR)(24) (SR = 2,4-dimethylbenzenethiolate) exhibits distinctive pi MIDLINE HORIZONTAL ELLIPSIS pi stacking and anagostic interactions (indicated by substantially short AuMIDLINE HORIZONTAL ELLIPSISH distances). Theoretical calculations reveal the increased energies of frontier orbitals for aromatic ligand-protected Au-38, indicating decreased electronic stability. However, this adverse effect could be compensated for by the AuMIDLINE HORIZONTAL ELLIPSISH-C interactions, which improve the geometric stability when ortho-substituted benzenethiols are used. Overall, this work reveals the substituent site effects based on the Au-38 model, and highlights the long-neglected anagostic interactions on the surface of Au-SR NCs which improve the structural stability.