Ligand Engineering toward the Trade‐Off between Stability and Activity in Cluster Catalysis

Abstract

We report the structures, stability and catalysis properties of two Ag 21 nanoclusters, namely [Ag 21 -(H 2 BTCA) 3 (O 2 PPh 2 ) 6 ]SbF 6 (1) and [Ag 21 (C�CC 6 [4]arene, R = OMe). Both Ag 21 structures possess an identical icosahedral kernel that is surrounded by eight peripheral Ag atoms. Single-crystal structural analysis and ESI-MS revealed that 1 is an 8-electron cluster and 2 has four free electrons. Theoretical results show that the P-symmetry orbitals are found as HOMO-1 and HOMO states in 1, and the frontier unoccupied molecular orbitals (LUMO, LUMO + 1 and LUMO + 2) show D-character, indicating 1 is a superatomic cluster with an electronically closed shell 1S 2 1P 6 , while 2 has an incomplete shell configuration 1S 2 1P 2 . These two Ag 21 clusters show superior stability under ambient conditions, and 1 is robust even at 90 °C in toluene and under oxidative conditions (30 % H 2 O 2 ). Significantly, 2 exhibits much higher activity than 1 as catalyst in the reduction of 4-nitrophenol. This work demonstrates that ligands can influence the electronic structures of silver clusters, and further affect their stability and catalytic performance.

Robust Enantiomeric Two-Dimensional Assembly of Atomically Precise Silver Clusters

“…9−12 In addition to modulating the core size, 13 stability, 14 and supramolecular assembly 9 of metal clusters, the employed surface-protecting ligands will also render physical and chemical properties of metal clusters including molecular chirality, 15 photoluminescence, 16 solubility, 17 and catalysis. 18 To date, chiral metal clusters protected by surface ligands have been attracting considerable research attention given their potential applications in enantioselective catalysis, chiral separation/recognition, sensing, biomedicine, and nonlinear optics. 3,7,19−24 Among various chiral metal clusters, most of them have been focused on the construction of atomically precise gold clusters; 19,23−34 in contrast, the preparation of Ag clusters with well-defined structures are still in their early stage of research advancement.…”

“…On the other hand, the stability of structurally well-defined Ag clusters is always a major concern especially in the case of using weak monothiolate ligands. 14,18 To solve this problem, an efficient strategy is to assemble discrete zero-dimensional (0D) metal clusters into a 1D cluster-based chain or 2D/3D frameworks. 46−56 Those assembled metal clusters could adopt advantages of enriched structural diversity and enhanced molecular robustness.…”

“…Atomically precise metal clusters have been emerging as a promising class of materials bridging the gap between molecules and metal nanoparticles, which have attracted much attention due to their precise chemical compositions and intriguing physicochemical properties. − A number of strategies have been developed to control the structure, size, composition, and property of metal clusters; among those, the surface-capping ligand design plays a vital role in determining the structures and properties of metal clusters. , Also, such a surface-capping ligand induced strategy is an efficient approach for intercluster assemblies of clusters in crystal lattices. − In addition to modulating the core size, stability, and supramolecular assembly of metal clusters, the employed surface-protecting ligands will also render physical and chemical properties of metal clusters including molecular chirality, photoluminescence, solubility, and catalysis …”

“…To date, chiral metal clusters protected by surface ligands have been attracting considerable research attention given their potential applications in enantioselective catalysis, chiral separation/recognition, sensing, biomedicine, and nonlinear optics. ,,− Among various chiral metal clusters, most of them have been focused on the construction of atomically precise gold clusters; ,− in contrast, the preparation of Ag clusters with well-defined structures are still in their early stage of research advancement. ,− Moreover, the origin of the chirality of these chiral Ag clusters can be mainly classified as three categories: (a) chirality induced by surface chiral ligands, − (b) postmodification of achiral Ag clusters using chiral ligands, ,− and (c) chiral metallic cores of the Ag clusters with achiral ligands. , However, the synthesis of chiral Ag clusters without a chiral metallic core using achiral ligands has yet to be reported. On the other hand, the stability of structurally well-defined Ag clusters is always a major concern especially in the case of using weak monothiolate ligands. , To solve this problem, an efficient strategy is to assemble discrete zero-dimensional (0D) metal clusters into a 1D cluster-based chain or 2D/3D frameworks. − Those assembled metal clusters could adopt advantages of enriched structural diversity and enhanced molecular robustness. For instance, Zhu and co-workers reported that the introduction of a SbF 6 – linker could render the assembled 3D superatom complex inorganic framework physical properties of larger channels, special circularly polarized luminescence behavior, and increased stability .…”

Site-specific sulfur-for-metal replacement in a silver nanocluster

“…[18][19][20][21][22][23] Even though the precise addition or removal of the components for specific nanoclusters has achieved some impressive results, most of them were inevitably triggered under severe conditions and thus appear challenging. [24][25][26][27] Compared to the strategy of removal or addition, traditional replacement including ligand exchange [28][29][30][31][32][33] and foreign metal doping [34][35][36][37][38][39] is a general method to modify a nanocluster without changing the overall structure. [40][41][42][43] In contrast to the traditional replacement, mutual substitution between nonmetal atoms and metal atoms not only inherits the merits of replacement (keeps other parts intact), but also possesses predictable characteristics such as increasing nanocluster nuclearity, modulating the electronic configuration.…”