Au 38 (SPh) 24 : Au 38 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 R = -SC6 H13 , -SC12 H25 and -SCH2 CH2 Ph. Au38 (SCH2 CH2 Ph)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.