Au-38(SPh)(24): Au-38 Protected with Aromatic Thiolate Ligands

Au-38(SR)(24) is one of the most extensively investigated gold nanomolecules along with Au-25(SR)(18) and Au-144(SR)(60). However, so far it has only been prepared using aliphatic-like ligands, where R = -SC6H13, -SC12H25 and -SCH2CH2Ph. Au-38(SCH2CH2Ph)(24) when reacted with HSPh undergoes core-size conversion to Au-36(SPh)(24), and existing literature suggests that Au-38(SPh)(24) cannot be synthesized. Here, contrary to prevailing knowledge, we demonstrate that Au-38(SPh)(24) can be prepared if the ligand exchanged conditions are optimized, under delicate conditions, without any formation of Au-36(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 Au-38(SPh)(24) in a solid glass form showing distinct differences from that of Au-38(S-aliphatic)(24). Theoretical analysis confirms experimental assignment of the optical spectrum and shows that the stability of Au-38(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 Au-38(SPh)(24) is stable at RT, it converts to Au-36(SPh)(24) either on prolonged etching (longer than 2 hours) at RT or when etched at 80 degrees C.