Heterogeneous catalysis involves solid-state catalysts, among which metal nanoparticles occupy an important position. Unfortunately, no two nanoparticles from conventional synthesis are the same at the atomic level, though such regular nanoparticles can be highly uniform at the nanometer level (e.g., size distribution ∼5%). In the long pursuit of well-defined nanocatalysts, a recent success is the synthesis of atomically precise metal nanoclusters protected by ligands in the size range from tens to hundreds of metal atoms (equivalently 1−3 nm in core diameter). More importantly, such nanoclusters have been crystallographically characterized, just like the protein structures in enzyme catalysis. Such atomically precise metal nanoclusters merge the features of well-defined homogeneous catalysts (e.g., ligand-protected metal centers) and enzymes (e.g., protein-encapsulated metal clusters of a few atoms bridged by ligands). The well-defined nanoclusters with their total structures available constitute a new class of model catalysts and hold great promise in fundamental catalysis research, including the atomically precise size dependent activity, control of catalytic selectivity by metal structure and surface ligands, structure−property relationships at the atomic-level, insights into molecular activation and catalytic mechanisms, and the identification of active sites on nanocatalysts. This Review summarizes the progress in the utilization of atomically precise metal nanoclusters for catalysis. These nanocluster-based model catalysts have enabled heterogeneous catalysis research at the single-atom and single-electron levels. Future efforts are expected to achieve more exciting progress in fundamental understanding of the catalytic mechanisms, the tailoring of active sites at the atomic level, and the design of new catalysts with high selectivity and activity under mild conditions.

CONSPECTUS:The chalcogenolato silver and copper superatoms are currently a topic of cutting edge research besides the extensively studied Au n (SR) m clusters. The crystal structural analysis is an indispensable tool to gain deep insights into the anatomy of these subnanometer clusters. The metal framework and spatial arrangement of the chalcogenolates around the metal core assist in unravelling the structure-property relationship and fundamental mechanistic involved in their fabrication. In this Account, we discuss our contribution towards the development of dichalcogenolato Ag and Cu cluster chemistry covering their fabrications and precise molecular structures. Briefly introducing the significance of the single crystal structures of the atomically precise clusters; the novel dichalcogenolated 2-electron superatomic copper and their alloy systems are presented first. The [Cu 13 {S 2 CNR} 6 {C≡CR'} 4 ] + is so far the first unique copper cluster having Cu 13 centred cuboctahedron, which is a miniature of bulk fcc. The galvanic exchange of the central Cu with Ag/Au results in a similar anatomy of formed bimetallic [Au/Ag@Cu 12 (S 2 CN n Bu 2 ) 6 (C≡CPh) 4 ][CuCl 2 ] species. This is unique in a sense that other contemporary M 13 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 1 yield enhancement of the doped species [Au@Cu 12 (S 2 CN n Bu 2 ) 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 [Ag 21 {S 2 P(O i Pr) 2 } 12 ] + , [Ag 20 {S 2 P(O i Pr) 2 } 12 ] and [Au@Ag 19 {S 2 P(OPr) 2 } 12 ]. They exhibit a non-hollow M 13 (Ag or AuAg 12 ) 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 [Ag 20 {S 2 P(O i Pr)} 12 ] cluster provides the first structural evidence of silver superatom with a chiral metallic core. This chirality arises through the simple removal of one of capping Ag + cation of [Ag 21 {S 2 P(O i Pr) 2 } 12 ] + present on its C 3 axis. Further, the effects of the ligand exchange on the structures of [Ag 20 {Se 2 P(O i Pr) 2 } 12 ], [Ag 21 {Se 2 P(OEt) 2 } 12 ] + and [AuAg 20 {Se 2 P(OEt) 2 } 12 ] + are studied extensively. The structure of the former species is similar to its dithiophosphate counterpart (C 3 symmetry). The latter two (T symmetry) differ in the arrangement of 8 capping Ag atoms, as they form a cube engraving the Ag 13 (AuAg 12 ) icosahedron. The blue shifts in absorption spectra and photoluminescence further indicate the strong influence of ...

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