Enhanced Surface Ligands Reactivity of Metal Clusters by Bulky Ligands for Controlling Optical and Chiral Properties

Abstract

Surface ligands play critical roles in determining the surface properties of metal clusters. However, modulating the properties and controlling the surface structure of clusters through surface‐capping agent displacement remain a challenge. In this work, a silver cluster, [Ag 14 (SPh(CF 3 ) 2 ) 12 (PPh 3 ) 4 (DMF) 4 ] ( Ag 14 ‐DMF , where HSPh(CF 3 ) 2 is 3,5‐bis(trifluoromethyl)benzenethiol, PPh 3 is triphenylphosphine and DMF is N,N‐Dimethylformamide), with weakly coordinated DMF ligands on the surface silver sites, was synthesized by using a mixed ligands strategy (bulky thiolates, phosphines and small solvents). The as‐prepared Ag 14 ‐DMF is a racemic mixture of chiral molecules. Owing to the unusually high surface reactivity of Ag 14 ‐DMF , the surface ligands are labile, easily dissociated or exchanged by other ligands. Based on the enhanced surface reactivity, easy modulation on the optical properties of Ag 14 by reversible “on‐off” DMF ligation was realized. The mechanism was unraveled and rationalized by density functional theory (DFT) calculations. When chiral amines were introduced to as‐prepared products, all eight surface ligands were replaced by amines and the racemic Ag 14 clusters were converted to optically pure homochiral Ag 14 clusters as evidenced by circular dichroism (CD) activity and single‐crystal X‐ray diffraction (SCXRD). This work not only provides a new insight as to how to modulate the optical properties of metal clusters, but also unveils an efficient way to obtain atomically precise homochiral clusters for specific applications.