Chiral footprint of the ligand layer in the all-alkynyl-protected gold nanocluster Au(CCPhF)

The electronic structure and chiroptical properties of the recently isolated and structurally characterized all-alkynyl-protected gold nanocluster Au(CCPhF) were analyzed via density functional theory (DFT) computations and compared to those of the structurally similar all-thiolate-protected Au(SCHPh). While DFT predicts very strong CD signals of similar strength for both clusters, the origins of chiroptical activity are markedly different. The chiral response of Au(CCPhF) originates only from the footprint of the outermost gold-ligand layer of 30 FPhCC-Au-CCPhF units covering an achiral I-symmetric Au core whereas the Au core of the Au(SCHPh) cluster has a chiral I symmetry and it alone produces CD signals that are comparable to those of the well-studied chiral Au(SR). These signals are then amplified by a chiral arrangement of the protecting 30 PhHCS-Au-SCHPh units. These results shed light on the origins of chiroptical activity of ligand-protected gold clusters that form an important class of atom-precise nanomaterials with potential applications in chiral sensing and enantioselective catalysis.