Alkynyl-Protected Chiral Bimetallic Ag22Cu7 Superatom with Multiple Chirality Origins

Abstract

Understanding the origin of chirality in the nanostructured materials is essential for chiroptical and catalytic applications. Here we report a chiral AgCu superatomic cluster, [Ag22Cu7(C≡CR)16(PPh3)5Cl6](PPh4), Ag22Cu7, protected by an achiral alkynyl ligand (HC≡CR: 3,5-bis(trifluoromethyl)phenylacetylene). Its crystal structure comprises a rare interpenetrating biicosahedral Ag17Cu2 core, which is stabilized by four different types of motifs: one Cu(C≡CR)2, four −C≡CR, two chlorides and one helical Ag5Cu4(C≡CR)10(PPh3)5Cl4. Structural analysis reveals that Ag22Cu7 exhibits multiple chirality origins, including the metal core, the metal-ligand interface and the ligand layer. Furthermore, the circular dichroism spectra of R/S-Ag22Cu7 are obtained by employing appropriate chiral molecules as optical enrichment agents. DFT calculations show that Ag22Cu7 is an eight-electron superatom, confirm that the cluster is chirally active, and help to analyze the origins of the circular dichroism.