Advances in Cu nanocluster catalyst design: recent progress and promising applications

Polymorphism of [Cu15(PhCH2CH2S)13(PPh3)6][BF4]2 and Double-Helical Assembly of [Cu18H(PhCH2CH2S)14(PPh3)6Cl3]: Origin of Two Chiral Nanoclusters with Triple-Helical Core from Intermediates

Here, we report the solvent-induced polymorphism in [Cu15(PET)13(TPP)6][BF4]2(Cu15) (TPP = triphenylphosphine, PET = 2-phenylethanthiol), and double-helical assembly of the [Cu18H(PET)14(TPP)6Cl3] (Cu18) nanocluster (NC) from reaction intermediates. Both copper NCs have an intrinsically chiral triple-stranded helicate metal core, unlike traditional copper NCs with a polyhedral-based kernel. The chiral structure of Cu15 resembles an enantiomeric pair in the unit cell. Moreover, Cu18 has a three-layered 3D chirality of a sandwich constructed of sulfur-bridged copper NCs aligned in a top-middle-down configuration. Furthermore, the Cu18 NC self-hierarchically assembles into a complex double-stranded helix secondary structure sustained by noncovalent interactions. Electrospray ionization mass spectrometry (ESI-MS), density functional theory (DFT), and X-ray photoelectron spectroscopy (XPS) were utilized to validate the single-crystal X-ray diffraction (SCXRD) data. Overall, this study provides an interesting example of polymorphism, chirality, and hierarchical double-helical assembly of NCs, allowing for extensive understanding of complicated structures at the atomic level.

Exploring the structural evolution of Cu-thiolate nanoclusters and their property correlations

Research on copper nanoclusters (Cu NCs) is expanding rapidly due to their remarkable structural versatility and related tunable properties they exhibit. This fast-paced development creates a need for a comprehensive overview of the structural evolution of Cu NCs, especially regarding how different geometric configurations emerge from variations in the ligand choice. In light of this, this feature article focuses on the role of thiolate ligands in shaping the structural and electronic properties of Cu NCs, with a particular emphasis on how modifications of ligands influence the geometry of NCs. While thiolates play a central role in stabilizing Cu NCs, this feature article also underscores the significance of co-ligands-such as hydrides, phosphines, and halides-because relying solely on thiolates is often insufficient to fully protect the surface of Cu NCs, unlike in the case of gold or silver NCs. A detailed analysis of how various thiolates and co-ligands affect core geometry reveals a direct correlation with the electronic properties of Cu NCs, which in turn influences their optical behavior. By examining these ligand-driven structural and electronic changes, this feature article aims to provide a deeper understanding of the relationship between ligand design and the resulting NC properties. The ultimate goal is to offer a strategy for the rational design of Cu NCs with tailored functionalities, thereby advancing NC chemistry and opening up new possibilities for applications in optoelectronics, catalysis, and sensing.

Designed construction of two new atom-precise three-dimensional and two-dimensional Ag12 cluster-assembled materials

Silver cluster-assembled materials (SCAMs) are well-defined crystalline extended materials hallmarked by their unique geometric structures, atomically precise designability and functional modularity. In this study, we report for the first time the synthesis of a (3,6)-connected three-dimensional (3D) SCAM, [Ag12(StBu)6(CF3COO)6(TPMA)6]n (designated as TUS 6), TPMA = tris(pyridine-4-ylmethyl)amine, by assembling Ag12 cluster nodes with the help of a tritopic linker TPMA. Besides, we also prepared a two-dimensional (2D) SCAM, [Ag12(StBu)6(CF3COO)6(TPEB)6]n (described as TUS 7), TPEB = 1,3,5-tris(pyridine-4-ylethynyl)benzene, by reticulating Ag12 nodes with a tritopic linker TPEB. Characterized by microscopic and diffraction analyses, the SCAMs revealed distinct morphologies, structural robustness, and phase purity. This paper elucidates how the binding with the organic linkers alters the symmetry of the silver nanoclusters (NCs). Changes in the symmetry of discrete NCs to assembled structures have not been reported yet. This study provides an atomic-level explanation of the transformation of symmetry from NCs to extended structures.

Ligand-Dependent Intracluster Interactions in Electrochemical CO2 Reduction Using Cu14 Nanoclusters

The electrochemical CO2 reduction reaction (CO2RR) has been extensively studied because it can be leveraged to directly convert CO2 into valuable hydrocarbons. Among the various catalysts, copper nanoclusters (Cu NCs) exhibit high selectivity and efficiency for producing CO2RR products owing to their unique geometric/electronic structures. However, the influence of protective ligands on the CO2RR performance of Cu NCs remains unclear. In this study, it is shown that different thiolate ligands, despite having nearly identical geometries, can substantially affect the electrochemical stability of Cu14 NCs in the CO2RR. Notably, Cu14 NCs protected by 2-phenylethanethiolate exhibit greater stability and achieve a relatively higher selectivity (≈40%) for formic acid production compared with the cyclohexanethiolate-protected counterpart. These insights are crucial for designing Cu NCs that are both stable and highly selective, enhancing their efficacy for electrochemical CO2 reduction.

Copper nanoclusters: emerging photoredox catalysts for organic bond formations

Advancements in fine chemical synthesis and drug discovery continuously demand the development of new and more efficient catalytic systems. In this regard, numerous transition metal-based catalysts have been developed and successfully applied in industrial processes. However, the need for innovative catalyst systems to further enhance the efficiency of chemical transformations and industrial applications persists. Metal nanoclusters (NCs) represent a distinct class of ultra-small nanoparticles (<3 nm) characterized by a precise number of metal atoms coordinated with a defined number of ligands. This structure confers abundant unsaturated active sites and unique electronic and optical properties, setting them apart from conventional nanoparticles or bulk metals. The well-defined structure and monodisperse nature of NCs make them particularly attractive for catalytic applications. Among these, copper-based nanoclusters have emerged as versatile and sustainable catalysts for challenging organic bond-forming reactions. Their unique properties, including natural abundance, accessible oxidation states, diverse ligand architectures, and strong photophysical characteristics, contribute to their growing prominence in this field. In this review, we discuss the photocatalytic activities of Cu-based nanoclusters, focusing on their applications in cross-coupling reactions (C-C and C-N), click reactions, multicomponent couplings, and oxidation reactions.

Controllable Preparation of a Cu NCs@Zn-MOF Hybrid with Dual Emission Induced by an Ion Exchange Strategy for the Detection of Explosives

The precise synthesis of Cu NCs is a highly desirable and controllable route for the preparation of desired structures and properties, which facilitates the rational design of valuable probes for fluorescence sensing and the understanding of structure-property relationships. Herein, an ion-exchange strategy combined with a bottom-up synthetic approach was utilized in the synthesis process of Cu NCs for the first time, which achieved the controllable synthesis of Cu NCs and in situ anchoring of Cu NCs on the support material HPU-14. The as-prepared Cu NCs@HPU-14-4h not only had a good peroxidase-like property but also exhibited stable dual-emitting fluorescence at 470 and 620 nm. Notably, the peroxidase-like property endowed Cu NCs@HPU-14-4h with the capability of highly sensitive colorimetric detection of H2O2 in a linear concentration from 0.1 to 140 μM (detection limit of 86.7 nM), and a change in the fluorescent color from red to blue could be observed by the naked eye. Furthermore, due to the large overlap between the absorption of 2,4,6-trinitrophenol (TNP) and the excitation band of Cu NCs@HPU-14-4h, TNP could also be detected from 27 types of analogs and common ions with a limit of detection of 68 nM. Finally, a portable hydrogel probe with efficient wipe sampling was fabricated by polyvinyl alcohol (PVA) comprising Cu NCs@HPU-14-4h with the aim of on-site visualization of different explosives. Consequently, the current study not only provides a new idea for the precise synthesis of Cu NCs and their controllable anchoring on support materials but also offers an effective method for predicting H2O2 and TNP.

Hydrogen production catalysed by atomically precise metal clusters

Atomically precise metal clusters that possess the exact atom number, definitive composition, and tunable geometric and electronic structures have emerged as ideal model catalysts for many important chemical processes. Recently, metal clusters have been widely used as excellent catalysts for hydrogen production to explore the relationship between the structure and catalytic properties at the atomic level. In this review, we systematically summarize the significant developments concerning metal clusters as electrocatalysts and photocatalysts for hydrogen generation. This review also puts forward the challenges and perspectives of atomically precise metal clusters in electrocatalysis and photocatalysis in the hope of providing a valuable reference for the rational design of high-performance catalysts for hydrogen production.

Exploring the impact of various reducing agents on Cu nanocluster synthesis

The synthesis of copper (Cu) nanoclusters (NCs) has experienced significant advancements in recent years. Despite the exploration of metal NCs dating back almost two decades, challenges specific to Cu NC synthesis arise from the variable oxidation states and heightened reactivity of intermediate Cu complexes, distinguishing it from its analogous counterparts. In this study, we present a comprehensive overview of this newly evolving research domain, focusing on the synthetic aspects. We delve into various factors influencing the synthesis of Cu NCs, with specific emphasis on the role of reducing agents. The impact of the reducing agent is particularly pivotal in this synthetic process, ultimately influencing the formation of model M(0)-containing NCs, which are less readily accessible in the context of Cu NCs. We anticipate that this frontier article will pave the way for accelerated research in the field of Cu NCs. By aiding in the selection of specific reaction conditions and reducing agents, we believe that this work will contribute to a faster-paced exploration of Cu NCs, further advancing our understanding and applications in this exciting area of nanomaterial research.

Construction of novel Ag(0)-containing silver nanoclusters by regulating auxiliary phosphine ligands

Controlled synthesis of metal clusters through minor changes in surface ligands holds significant interest because the corresponding entities serve as ideal models for investigating the ligand environment's stereochemical and electronic contributions that impact the corresponding structures and properties of metal clusters. In this work, we obtained two Ag(0)-containing nanoclusters (Ag17 and Ag32) with near-infrared emissions by regulating phosphine auxiliary ligands. Ag17 and Ag32 bear similar shells wherein Ag17 features a trigonal bipyramid Ag5 kernel while Ag32 has a bi-icosahedral interpenetrating an Ag20 kernel. Ag17 and Ag32 showed a near-infrared emission (NIR) of around 830 nm. Benefiting from the rigid structure, Ag17 displayed a more intense near-infrared emission than Ag32. This work provides new insight into the construction of novel superatomic silver nanoclusters by regulating phosphine ligands.

Doping effect on a two-electron silver nanocluster

This study investigates the effects of metal addition and doping of a 2-electron silver superatom, [Ag10{S2P(OiPr)2}8] (Ag10). When Ag+ is added to Ag10 in THF solution, [Ag11{S2P(OiPr)2}8(OTf)] (Ag11) is rapidly formed almost quantitatively. When the same method is used with Cu+, a mixture of alloys, [CuxAg11-x{S2P(OiPr)2}8]+ (x = 1-3, CuxAg11-x), is obtained. In contrast, introducing Au+ to Ag10 leads to decomposition. The structural and compositional analysis of Ag11 was characterized by single-crystal X-ray diffraction (SCXRD), ESI-MS, NMR spectroscopy, and DFT calculations. While no crystal structure was obtained for CuxAg11-x, DFT calculations provide insights into potential sites for copper location. The absorption spectrum exhibits a notable blue shift in the low-energy band after copper doping, contrasting with that of the slight shift observed in 8-electron Cu-doped Ag nanoclusters. Ag11 and CuxAg11-x are strongly emissive at room temperature, and solvatochromism across different organic solvents is highlighted. This study underscores the profound influence of metal addition and doping on the structural and optical properties of silver nanoclusters, providing important contributions to understanding the nanoclusters and their photophysical behaviors.

A thiolated copper-hydride nanocluster with chloride bridging as a catalyst for carbonylative C-N coupling of aryl amines under mild conditions: a combined experimental and theoretical study

Atomically precise copper nanoclusters (Cu NCs), an emerging class of nanomaterials, have garnered significant attention owing to their versatile core-shell architecture and their potential applications in catalytic reactions. In this study, we present a straightforward synthesis strategy for [Cu29(StBu)12(PPh3)4Cl6H10][BF4] (Cu29) NCs and explore their catalytic activity in the carbonylative C-N coupling reaction involving aromatic amines and N-heteroarenes with dialkyl azodicarboxylates. Through a combination of experimental investigations and density functional theory studies, we elucidate the radical mechanisms at play. The crucial step in the catalytic process is identified as the decomposition of diisopropyl azodicarboxylates on the surface of Cu29 NCs, leading to the generation of oxyacyl radicals and the liberation of nitrogen gas. Subsequently, an oxyacyl radical abstracts a hydrogen atom from aniline, initiating the formation of an aminyl radical. Finally, the aminyl radical reacts with another oxyacyl radical, culminating in the synthesis of the desired carbamate product. This detailed analysis provides insights into the intricate catalytic pathways of Cu29 NCs, shedding light on their potential for catalyzing carbonylative C-N coupling reactions.

A Comprehensive Analysis of Luminescent Crystallized Cu Nanoclusters

Photoluminescence (PL) emission is an intriguing characteristic displayed by atomically precise d10 metal nanoclusters (NCs), renowned for their meticulous atomic arrangements, which have captivated the scientific community. Cu(I) NCs are a focal point in extensive research due to their abundance, cost-effectiveness, and unique luminescent attributes. Despite similar core sizes, their luminescent characteristics vary, influenced by multiple factors. Progress hinges on synthesizing new NCs and modifying existing ones, with postsynthetic alterations impacting emission properties. The rapid advancements in this field pose challenges in discerning essential points for excelling amidst competition with other d10 NCs. This Perspective explores the intricate origins of PL emission in Cu(I) NCs, providing a comprehensive review of their correlated structural architectures. Understanding the mechanistic origin of PL emission in each cluster is crucial for correlating diverse characteristics, contributing to a deeper comprehension from both fundamental and applied scientific perspectives.

Gold Nanoclusters Synthesized within Single-Chain Nanoparticles as Catalytic Nanoreactors in Water

Metalloenzymes are able to catalyze complex biochemical reactions in cellular (aqueous) media with high efficiency. In recent years, a variety of metal-containing single-chain nanoparticles (SCNPs) have been synthesized as simplified metalloenzyme-mimetic nano-objects. However, most of the metal-containing SCNPs reported so far contained complexed metal ions but not metal nanoclusters (NCs) with diameter <5 nm, which could be used as powerful, emerging catalysts. Herein, we report the synthesis of gold nanoclusters (Au-NCs) within SCNPs and the further use of Au-NCs/SCNPs as catalytic nanoreactors in water. We demonstrate that a common motif contained in several drugs (i.e., the aminophenyl-oxazolidinone fragment present in Rivaroxaban, Sutezolid, and Linezolid) can be efficiently prepared in water from a hydrophobic precursor compound by using the Au-NCs/SCNPs as efficient catalytic nanoreactors. In summary, this work paves the way forthe synthesis of metal-NCs/SCNPs for advanced catalysis in aqueous media.

Atom-Precise Ligated Copper and Copper-Rich Nanoclusters with Mixed-Valent Cu(I)/Cu(0) Character: Structure-Electron Count Relationships

Copper homometallic and copper-rich heterometallic nanoclusters with some Cu(0) character are reviewed. Their structure and stability are discussed in terms of their number of "free" electrons. In many aspects, this structural chemistry differs from that of their silver or copper homologs. Whereas the two-electron species are by far the most numerous, only one eight-electron species is known, but more electron-rich nanoclusters have also been reported. Owing to the relatively recent development of this chemistry, it is likely that more electron-rich species will be reported in the future.