Controlling the Atomic Structure of Au30 Nanoclusters by a Ligand-Based Strategy

Recent Advances in Ligand Engineering for Gold Nanocluster Catalysis: Ligand Library, Ligand Effects and Strategies

Advances in new ligands in the last decade facilitated in-depth studies on the property-relationship of gold nanoclusters and promoted the rational synthesis and related applications of such materials. Currently, more and more new ligands are being explored; thus, the ligand library of AuNCs is being expanded fast, which also enables investigation of ligand effects of AuNCs via direct comparison of different ligating shell with the identical gold core. It is now widely accepted that ligands influence the properties of AuNCs enormously including stability, catalysis, photoluminescence among others. These studies inspired ligand engineering of AuNCs. One of the goals for ligand engineering is to develop ligated AuNC catalysts in which the ligands are able to exert big-enough influence on electronic and steric control over catalysis as in a transition-metal or an enzyme system. Although increasing attention is paid to the further expansion of ligand library, the investigation of design principles and strategies regarding ligands are still in their infant stage. This review summarizes the ligands for AuNC synthesis, the ligand effects on stability and catalysis, and recently developed strategies in promoting AuNC catalytic performance via ligand manipulation.

Electrocatalytic CO2 Reduction over Atomically Precise Metal Nanoclusters Protected by Organic Ligands

The electrochemical carbon dioxide reduction reaction (CO₂RR) is a promising method to realize carbon recycling and sustainable development because of its mild reaction conditions and capability to utilize the electric power generated by renewable energy such as solar, wind, or tidal energy to produce high-value-added liquid fuels and chemicals. However, it is still a great challenge to deeply understand the reaction mechanism of CO₂RRs involving multiple chemical processes and multiple products due to the complexity of the traditional catalyst's surface. Organic ligand-protected metal nanoclusters (NCs) with accurate compositions and definite atom packing structures show advantages for revealing the reaction mechanism of CO₂RRs. This Review focuses on the recent progress in CO₂RRs catalyzed by atomically precise metal NCs, including gold, copper, and silver NCs. Particularly, the influences of charge, ligand, surface structure, doping of Au NCs, and binders on the CO₂RR are discussed in detail. Meanwhile the reaction mechanisms of CO₂RRs including the active sites and the key reaction intermediates are also discussed. It is expected that progress in this research area could promote the development of metal NCs and CO₂RRs.

The New Ag-S Cluster [Ag50S13(StBu)20][CF3COO]4 with a Unique hcp Ag14 Kernel and Ag36 Keplerian-Shell-Based Structural Architecture and Its Photoresponsivity

In metal nanoclusters (NCs), the kernel geometry and the nature of the surface protecting ligands are very crucial for their structural stability and properties. The synthesis and structural elucidation of Ag NCs is challenging because the zerovalent oxidation state of Ag is very reactive and prone to oxidization. Here, we report the NC [Ag₅₀S₁₃(S^tBu)₂₀][CF₃COO]₄ with a hexagonal close-packed (hcp) cagelike Ag₁₄ kernel. A truncated cubic shell and an octahedral shell encapsulate the hcp-layered kernel via an interstitial S^2- anionic shell to form an Ag₃₆ Keplerian outer shell of the NC. A theoretical study indicates the stability of this NC in its 4+ charge state and the charge distribution between the kernel and Keplerian shell. The unprecedented electronic structure facilitates its application toward sustainable photoresponse properties. The new insights into this novel Ag NC kernel and Keplerian shell structure may pave the way to understanding the unique structure and developing electronic structure-based applications.

A theoretical study of the monolayer-protected gold cluster Au317(SR)110

Significant efforts have been made to uncover the structures of monolayer-protected gold nanoclusters. However, the synthesis, crystallization, and structural analysis of gold nanoclusters with over 300 metal atoms is a grand challenge. In this work, a new gold nanocluster containing 317 gold atoms and 110 thiolate (SH) ligands (referred to as Au₃₁₇(SH)₁₁₀) is theoretically studied, which is larger in size than the formerly reported Au₂₇₉(SR)₈₄ cluster. The stability of the Au₃₁₇(SH)₁₁₀ cluster is studied based on calculations of the averaged cluster formation energy (E_ave), indicating that Au₃₁₇(SH)₁₁₀ has good structural stability and that the SPhCOOH (p-MBA) ligand is a good candidate for stabilizing the cluster. The calculation of density of state and the time-dependent density functional theory (TD-DFT) calculations of the optical absorption properties show that Au₃₁₇(SH)₁₁₀ is in a metallic state.

The ligand effect of atomically precise gold nanoclusters in tailoring catalytic properties

It is well known that surface ligands are vital layers for ligand-protected Au_n nanoclusters. Improving the knowledge of the relationship between ligands and catalytic properties is a forefront research topic for Au_n nanoclusters. Enormous effort has been devoted to realizing the ligand effect in synthesis, including well-controlled sizes and shapes as well as structural transformation. However, the crucial function of surface ligands has not been addressed yet in catalytic reactions. Here, this review mainly aims to summarize the recent progress concerning the influence of surface ligand layers on catalytic activity and selectivity, based on the various types of ligand protected Au_n nanoclusters. Besides, the potential challenges and opportunities of Au_n nanoclusters are indicated, mainly in terms of surface ligands to guide the improvement of catalytic performances.

Distinct chemical fixation of CO2 enabled by exotic gold nanoclusters

Atomically precise metal nanoclusters, especially the metal nanoclusters with an exotic core structure, have given rise to a great deal of interest in catalysis, attributing to their well-defined structures at the atomic level and consequently unique electronic properties. Herein, the catalytic performances of three gold nanoclusters, such as Au₃₈S₂(S-Adm)₂₀ with a body-centered cubic (bcc) kernel structure, Au₃₀(S-Adm)₁₈ with a hexagonal close-packed (hcp) core structure, and Au₂₁(S-Adm)₁₅ with a face-centered cubic (fcc) kernel structure, were attempted for the CO₂ cycloaddition with epoxides toward cyclic carbonates. Due to the excess positive charge with a strong Lewis acidity and large chemical adsorption capacity, the bcc-Au₃₈S₂(S-Adm)₂₀ nanocluster outperformed the hcp-Au₃₀(S-Adm)₁₈ and fcc-Au₂₁(S-Adm)₁₅ nanoclusters. Additionally, the synergistic effect between the gold nanocluster and co-catalyst played a crucial role in CO₂ cycloaddition.

Alternating Array Stacking of Ag26 Au and Ag24 Au Nanoclusters

An assembly strategy for metal nanoclusters using electrostatic interactions with weak interactions, such as C-H⋅⋅⋅π and π⋅⋅⋅π interactions in which cationic [Ag₂₆ Au(2-EBT)₁₈ (PPh₃ )₆ ]⁺ and anionic [Ag₂₄ Au(2-EBT)₁₈ ]^- nanoclusters gather and assemble in an unusual alternating array stacking structure is presented. [Ag₂₆ Au(2-EBT)₁₈ (PPh₃ )₆ ]⁺ [Ag₂₄ Au(2-EBT)₁₈ ]^- is a new compound type, a double nanocluster ion compound (DNIC). A single nanocluster ion compound (SNIC) [PPh₄ ]⁺ [Ag₂₄ Au(2-EBT)₁₈ ]^- was also synthesized, having a k-vector-differential crystallographic arrangement. [PPh₄ ]⁺ [Ag₂₄ Au(2,4-DMBT)₁₈ ]^- adopts a different assembly mode from both [Ag₂₆ Au(2-EBT)₁₈ (PPh₃ )₆ ]⁺ [Ag₂₄ Au(2-EBT)₁₈ ]^- and [PPh₄ ]⁺ [Ag₂₄ Au(2-EBT)₁₈ ]^- . Thus, the striking packing differences of [Ag₂₆ Au(2-EBT)₁₈ (PPh₃ )₆ ]⁺ [Ag₂₄ Au(2-EBT)₁₈ ]^- , [PPh₄ ]⁺ [Ag₂₄ Au(2-EBT)₁₈ ]^- and the existing [PPh₄ ]⁺ [Ag₂₄ Au(2,4-DMBT)₁₈ ]^- from each other indicate the notable influence of ligands and counterions on the self-assembly of nanoclusters.

Atomically Tailored Gold Nanoclusters for Catalytic Application

Recent advances in the synthetic chemistry of atomically precise metal nanoclusters (NCs) have significantly broadened the accessible sizes and structures. Such particles are well defined and have intriguing properties, thus, they are attractive for catalysis. Especially, those NCs with identical size but different core (or surface) structure provide unique opportunities that allow the specific role of the core and the surface to be mapped out without complication by the size effect. Herein, we summarize recent work with isomeric Au_n NCs protected by ligands and isostructural NCs but with different surface ligands. The highlighted work includes catalysis by spherical and rod-shaped Au₂₅ (with different ligands), quasi-isomeric Au₂₈ (SR)₂₀ with different R groups, structural isomers of Au₃₈ (SR)₂₄ (with identical R) and Au₃₈ S₂ (SR)₂₀ with body-centred cubic (bcc) structure, and isostructural [Au₃₈ L₂₀ (PPh₃ )₄ ]²⁺ (different L). These isomeric and/or isostructural NCs have provided valuable insights into the respective roles of the kernel, surface staples, and the type of ligands on catalysis. Future studies will lead to fundamental advances and development of tailor-made catalysts.