Structurally Precise Dichalcogenolate-Protected Copper and Silver Superatomic Nanoclusters and Their Alloys.

The chalcogenolato silver and copper superatoms are currently a topic of cutting edge research besides the extensively studied Au n(SR) m clusters. Crystal structure analysis is an indispensable tool to gain deep insights into the anatomy of these sub-nanometer clusters. The metal framework and spatial arrangement of the chalcogenolates around the metal core assist in unravelling the structure-property relationships and fundamental mechanisms involved in their fabrication. In this Account, we discuss our contribution toward the development of dichalcogenolato Ag and Cu cluster chemistry covering their fabrication and precise molecular structures. Briefly introducing the significance of the single crystal structures of the atomically precise clusters, the novel dichalcogenolated two-electron superatomic copper and its alloy systems are presented first. The [Cu13{S2CNR}6{C≡CR'}4]+ is so far the first unique copper cluster having Cu13 centered cuboctahedra, which is a miniature of bulk fcc structure. The galvanic exchange of the central Cu with Ag or Au results in a similar anatomy of formed bimetallic [Au/Ag@Cu12(S2CN nBu2)6(C≡CPh)4][CuCl2] species. This is unique in the sense that other contemporary M13 cores in group 11 superatomic chemistry are compact icosahedra. The central doping of Ag or Au significantly affects the physiochemical properties of the bimetallic Cu-rich clusters. It is manifested in the dramatic quantum yield enhancement of the doped species [Au@Cu12(S2CN nBu2)6(C≡CPh)4]+ with a value of 0.59 at 77 K in 2-MeTHF. In the second part, the novel eight-electron dithiophosphate- and diselenophosphate-protected silver systems are presented. A completely different type of architecture was revealed for the first time from the successful structural determination of [Ag21{S2P(O iPr)2}12]+, [Ag20{S2P(O iPr)2}12] and [Au@Ag19{S2P(OPr)2}12]. They exhibit a nonhollow M13 (Ag or AuAg12) icosahedron, capped by 8 and 7 Ag atoms in the former and latter two species, respectively. The overall metal core units are protected by 12 dithiophosphate ligands and the metal-ligand interface structure was found to be quite different from that of Au n(SR) m. Notably, the [Ag20{S2P(O iPr)}12] cluster provides the first structural evidence of a silver superatom with a chiral metallic core. This chirality arises through the simple removal of one of capping Ag+ cations of [Ag21{S2P(O iPr)2}12]+ present on its C3 axis. Further, the effects of the ligand exchange on the structures of [Ag20{Se2P(O iPr)2}12], [Ag21{Se2P(OEt)2}12]+, and [AuAg20{Se2P(OEt)2}12]+ are studied extensively. The structure of the former species is similar to its dithiophosphate counterpart ( C3 symmetry). The latter two ( T symmetry) differ in the arrangement of 8 capping Ag atoms, as they form a cube engraving the Ag13 (AuAg12) icosahedron. The blue shifts in absorption spectra and photoluminescence further indicate the strong influence of the central Au atom in the doped clusters. Finally, the first paradigm of unusual heteroatom doping induced size-structure transformations is discussed by presenting the case of formation of [Au3Ag18{Se2P(O iPr)2}12]+ upon Au doping into [Ag20{Se2P(O iPr)2}12]0. Finally, before concluding this Account, we discuss the possibility of many unique structural isomers with different physical properties for the aforementioned Ag superatoms which need to be explored extensively in the future.