Au₃₈(SPh)₂₄: Au₃₈ Protected with Aromatic Thiolate Ligands

Au₃₈(SR)₂₄ is one of the most extensively investigated gold nanomolecules along with Au₂₅(SR)₁₈ and Au₁₄₄(SR)₆₀. However, so far it has only been prepared using aliphatic-like ligands, where <i>R</i> = −SC₆H₁₃, −SC₁₂H₂₅ and −SCH₂CH₂Ph. Au₃₈(SCH₂CH₂Ph)₂₄ when reacted with HSPh undergoes core-size conversion to Au₃₆(SPh)₂₄, and existing literature suggests that Au₃₈(SPh)₂₄ cannot be synthesized. Here, contrary to prevailing knowledge, we demonstrate that Au₃₈(SPh)₂₄ can be prepared if the ligand exchanged conditions are optimized, under delicate conditions, without any formation of Au₃₆(SPh)₂₄. Conclusive evidence is presented in the form of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), electrospray ionization mass spectra (ESI-MS) characterization, and optical spectra of Au₃₈(SPh)₂₄ in a solid glass form showing distinct differences from that of Au₃₈(S-aliphatic)₂₄. Theoretical analysis confirms experimental assignment of the optical spectrum and shows that the stability of Au₃₈(SPh)₂₄ is not negligible with respect to that of its aliphatic analogous, and contains a significant component of ligand−ligand attractive interactions. Thus, while Au₃₈(SPh)₂₄ is stable at RT, it converts to Au₃₆(SPh)₂₄ either on prolonged etching (longer than 2 hours) at RT or when etched at 80 °C