Structural isomerism in gold nanoparticles revealed by X-ray crystallography. [Corrected]

'Passivated Precursor' Approach to All-Alkynyl-Protected Gold Nanoclusters and Total Structure Determination of Au130

A 'passivated precursor' approach is developed for the efficient synthesis and isolation of all-alkynyl-protected gold nanoclusters. Direct reduction of dpa-passivated precursor Au-dpa (Hdpa=2,2'-dipyridylamine) in one-pot under ambient conditions gives a series of clusters including Au22(C≡CR)18 (R=-C6H4-2-F), Au36(C≡CR)24, Au44(C≡CR)28, Au130(C≡CR)50, and Au144(C≡CR)60. These clusters can be well separated via column chromatography. The overall isolation yield of this series of clusters is 40 % (based on gold), which is much improved in comparison with previous approaches. It is notable that the molecular structure of the giant cluster Au130(C≡CR)50 is revealed, which presents important information for understanding the structure of the mysterious Au130 nanoclusters. Theoretical calculations indicated Au130(C≡CR)50 has a smaller HOMO-LUMO gap than Au130(S-C6H4-4-CH3)50. This facile and reliable synthetic approach will greatly accelerate further studies on all-alkynyl-protected gold nanoclusters.

Gold-Thiolate Nanocluster Dynamics and Intercluster Reactions Enabled by a Machine Learned Interatomic Potential

Monolayer protected metal clusters comprise a rich class of molecular systems and are promising candidate materials for a variety of applications. While a growing number of protected nanoclusters have been synthesized and characterized in crystalline forms, their dynamical behavior in solution, including prenucleation cluster formation, is not well understood due to limitations both in characterization and first-principles modeling techniques. Recent advancements in machine-learned interatomic potentials are rapidly enabling the study of complex interactions such as dynamical behavior and reactivity on the nanoscale. Here, we develop an Au-S-C-H atomic cluster expansion (ACE) interatomic potential for efficient and accurate molecular dynamics simulations of thiolate-protected gold nanoclusters (Aun(SCH3)m). Trained on more than 30,000 density functional theory calculations of gold nanoclusters, the interatomic potential exhibits ab initio level accuracy in energies and forces and replicates nanocluster dynamics including thermal vibration and chiral inversion. Long dynamics simulations (up to 0.1 μs time scale) reveal a mechanism explaining the thermal instability of neutral Au25(SR)18 clusters. Specifically, we observe multiple stages of isomerization of the Au25(SR)18 cluster, including a chiral isomer. Additionally, we simulate coalescence of two Au25(SR)18 clusters and observe series of clusters where the formation mechanisms are critically mediated by ligand exchange in the form of [Au-S]n rings.

Carboxylic acid isomer-directed synthesis of CdS nanocluster isomers

Selective synthesis of nanocluster (NC) isomers with tailored structures holds significant importance for enhancing their applications. Here, we develop an effective strategy for the selective synthesis of CdS NC isomers through the judicious choice of a pair of carboxylic acid isomer additives. Specifically, CdS NC-312 and NC-323 (denoted by their UV-vis absorption peak position) could be selectively produced by introducing a conventional mixture of Cd and S precursors, with the addition of 2-methylbutyric acid (2-MA) and 3-methylbutyric acid (3-MA), respectively. The synthesized NC isomers demonstrated a precise isomeric relationship, sharing both the isomeric inorganic core and organic surface. Alternatively, the as-synthesized NCs were interconvertible by re-adding the acid isomers. The density functional theory calculations further support that 2-MA and 3-MA have specific selectivity for producing CdS NC isomers by interfacial tuning. Finally, the generality of this methodology was also evidenced with applications in other CdS NC synthetic systems. This study unveils the intriguing correlation between additive structures and the configuration of NCs, providing a foundation for the selective synthesis of NC isomers.

DNA Framework-Guided Self-Limiting Aggregation for Highly Luminescent Metal Cluster Nanoaggregates

The photoluminescent properties of atomically precise metal nanoclusters (MCs) have garnered significant attention in the fields of chemical sensing and biological imaging. However, the limited brightness of single-component nanoclusters hinders their practical applications, and the conventional ligand engineering approaches have proven insufficient in enhancing the emission efficiency of MCs. Here, we present a DNA framework-guided strategy to prepare highly luminescent metal cluster nanoaggregates. Our approach involves an amphiphilic DNA framework comprising a hydrophobic alkyl core and a rigid DNA framework shell, serving as a nucleation site and providing well-defined nanoconfinements for the self-limiting aggregation of MCs. Through this method, we successfully produced homogeneous MC nanoaggregates (10.1 ± 1.2 nm) with remarkable nanoscale precision. Notably, this strategy proves adaptable to various MCs, leading to a substantial enhancement in emission and quantum yield, up to 3011- and 87-fold, respectively. Furthermore, our investigation using total internal reflection fluorescence microscopy at the single-particle level uncovered a more uniform photon number distribution and higher photostability for MC nanoaggregates compared to template-free counterparts. This DNA-templating strategy introduces a conceptually innovative approach for studying the photoluminescent properties of aggregates with nanoscale precision and holds promise for constructing highly luminescent MC nanoparticles for diverse applications.

Chemical Flexibility of Atomically Precise Metal Clusters

Ligand-protected metal clusters possess hybrid properties that seamlessly combine an inorganic core with an organic ligand shell, imparting them exceptional chemical flexibility and unlocking remarkable application potential in diverse fields. Leveraging chemical flexibility to expand the library of available materials and stimulate the development of new functionalities is becoming an increasingly pressing requirement. This Review focuses on the origin of chemical flexibility from the structural analysis, including intra-cluster bonding, inter-cluster interactions, cluster-environments interactions, metal-to-ligand ratios, and thermodynamic effects. In the introduction, we briefly outline the development of metal clusters and explain the differences and commonalities of M(I)/M(I/0) coinage metal clusters. Additionally, we distinguish the bonding characteristics of metal atoms in the inorganic core, which give rise to their distinct chemical flexibility. Section 2 delves into the structural analysis, bonding categories, and thermodynamic theories related to metal clusters. In the following sections 3 to 7, we primarily elucidate the mechanisms that trigger chemical flexibility, the dynamic processes in transformation, the resultant alterations in structure, and the ensuing modifications in physical-chemical properties. Section 8 presents the notable applications that have emerged from utilizing metal clusters and their assemblies. Finally, in section 9, we discuss future challenges and opportunities within this area.

Temperature-Controlled Selective Formation of Silver Nanoclusters and Their Transformation to the Same Product

Herein, two atomically precise silver nanoclusters, Ag54 and Ag33, directed by inner anion templates (CrO4 2- and/or Cl-), are initially isolated as a mixed phase from identical reactants across a wide temperature range (20-80 °C). Interestingly, fine-tuning the reaction temperature can realize pure phase synthesis of the two nanoclusters; that is, a metastable Ag54 is kinetically formed at a low temperature (20 °C), whereas such a system is steered towards a thermodynamically stable Ag33 at a relatively high temperature (80 °C). Electrospray ionization mass spectrometry illustrates that the stability of Ag33 is superior to that of Ag54, which is further supported by density functional theory calculations. Importantly, the difference in structural stability can influence the pathway of 1,4-bis(pyrid-4-yl)benzene induced transformation reaction starting from Ag54 and Ag33. The former undergoes a dramatic breakage-reorganization process to form an Ag31 dimer (Ag31), while the same product can be also achieved from the latter following a noninvasive ligand exchange process. Both the Ag54 and Ag33 have the potential for further remote laser ignition applications. This work not only demonstrates how temperature controls the isolation of a specific phase, but also sheds light on the structural transformation pathway of nanoclusters with different stability.

An insight, at the atomic level, into the structure and catalytic properties of the isomers of the Cu22 cluster

The study of structural isomerism in copper nanoclusters has been relatively limited compared to that in gold and silver nanoclusters. In this work, we present the controlled synthesis and structures of two isomeric copper nanoclusters, denoted as Cu22-1 and Cu22-2, whose compositions were determined to be Cu22(SePh)10(Se)6(P(Ph-4F)3)8 through single-crystal X-ray diffraction (SCXRD). The structural isomerism of Cu22-1 and Cu22-2 arises from the different arrangements of a few Cu(SeR)(PR3) motifs on the surface structure. These subtle changes in the surface structure also influence the distortion of the core and the spatial arrangement of the clusters, and affect the electronic structure. Furthermore, due to their distinct structures, Cu22-1 and Cu22-2 exhibit different catalytic properties in the copper-catalyzed [3 + 2] azide-alkyne cycloaddition (CuAAC). Notably, Cu22-1 demonstrates efficient catalytic activity for photoinduced AAC, achieving a yield of 90% within 1 hour. This research contributes to the understanding of structural isomerism in copper nanoclusters and offers insights into the structure-function relationship in these systems.

Concomitant Near-Infrared Photothermy and Photoluminescence of Rod-Shaped Au52(PET)32 and Au66(PET)38 Synthesized Concurrently

Gold nanoclusters exhibiting concomitant photothermy (PT) and photoluminescence (PL) under near-infrared (NIR) light irradiation are rarely reported, and some fundamental issues remain unresolved for such materials. Herein, we concurrently synthesized two novel rod-shaped Au nanoclusters, Au52(PET)32 and Au66(PET)38 (PET = 2-phenylethanethiolate), and precisely revealed that their kernels were 4 × 4 × 6 and 5 × 4 × 6 face-centered cubic (fcc) structures, respectively, based on the numbers of Au layers in the [100], [010], and [001] directions. Following the structural growth mode from Au52(PET)32 to Au66(PET)38, we predicted six more novel nanoclusters. The concurrent synthesis provides rational comparison of the two nanoclusters on the stability, absorption, emission and photothermy, and reveals the aspect ratio-related properties. An interesting finding is that the two nanoclusters exhibit concomitant PT and PL under 785 nm light irradiation, and the PT and PL are in balance, which was explained by the qualitative evaluation of the radiative and non-radiative rates. The ligand effects on PT and PL were also investigated.

Insight to the Catalytic Activity of Atomically Precise Ag4Ni2 Nanoclusters on Silicon Carbide for Nitroarene Reduction

Atomically precise Ag4Ni2 nanoclusters with 2,4-dimethylbenzenethiol as the ligands were synthesized and characterized as a cocatalyst of SiC for the selective hydrogenation of nitroarenes to arylamine in the presence of NaBH4. The obtained Ag4Ni2/SiC samples exhibited extraordinary catalytic activity, and a self-accelerated catalytic process was observed with the reduction of nitrophenol to aminophenol as the model reaction. Experimental comparison between the Ag4Ni2/SiC samples before and after the catalysis showed that the transformation of Ag4Ni2 clusters to polydisperse Ag particles as well as amorphous NiOx on the surface of SiC in the catalysis was the key to their high activity. AIMD calculations revealed that the transformation of Ag4Ni2 was driven by the presence of multiple hydrides on the cluster, which induced the detachment of the thiol ligand of the nanoclusters.

Aggregation Inducing Reversible Conformational Isomerization of Surface Staple in Au18SR14 Nanoclusters

The conformation of molecules and materials is crucial in determining their properties and applications. Here, this work explores the reversible transformation between two distinct conformational isomers in metal nanoclusters. This work demonstrates the successful manipulation of a controllable and reversible isomerization of Au18SR14 within an aqueous solution through two distinct methods: ethanol addition and pH adjustment. The initial driver is the alteration of the solution environment, leading to the aggregation of Au18SR14 protected by ligands with smaller steric hindrance. At the atomic level, the folding mode of the unique Au4SR5 staple underpins the observed structural transformation. The reversal of staple conformation leads to color shifting between green and orange-red, and tailors a second emission peak at 725 nm originating from charge transfer from the thiolate to the Au9 core. This work not only deepens the understanding of the surface structure and dual-emission of metal nanoparticles, but also enhances the comprehension of their isomerization.

Bright near-infrared emission from the Au39(SR)29 nanocluster

The synthesis of atomically precise gold nanoclusters with high photoluminescence quantum yield (PLQY) in the near-infrared (NIR) region and understanding their photoluminescence mechanism are crucial for both fundamental science and practical applications. Herein, we report a highly luminescent, molecularly pure Au39(PET)29 (PET = 2-phenylethanethiolate) nanocluster with PLQY of 19% in the NIR range (915 nm). Steady state and time-resolved PL analyses, as well as temperature-dependent PL measurements reveal the emission nature of Au39(PET)29, which consists of prompt fluorescence (weak), thermally activated delayed fluorescence (TADF), and phosphorescence (predominant). Furthermore, strong dipole-dipole interaction in the solid-state (e.g., Au39(PET)29 nanoclusters embedded in a polystyrene thin-film) is found to narrow the energy gap between the S1 and T1 states, which results in faster intersystem crossing and reverse intersystem crossing; thus, the ratio of TADF to phosphorescence varies and the total PLQY is increased to 32%. This highly luminescent nanocluster holds promise in imaging, sensing and optoelectronic applications.

Bottom-Up Construction of Metal-Organic Framework Loricae on Metal Nanoclusters with Consecutive Single Nonmetal Atom Tuning for Tailored Catalysis

The introduction of single or multiple heterometal atoms into metal nanoparticles is a well-known strategy for altering their structures (compositions) and properties. However, surface single nonmetal atom doping is challenging and rarely reported. For the first time, we have developed synthetic methods, realizing "surgery"-like, successive surface single nonmetal atom doping, replacement, and addition for ultrasmall metal nanoparticles (metal nanoclusters, NCs), and successfully synthesized and characterized three novel bcc metal NCs Au38I(S-Adm)19, Au38S(S-Adm)20, and Au38IS(S-Adm)19 (S-Adm: 1-adamantanethiolate). The influences of single nonmetal atom replacement and addition on the NC structure and optical properties (including absorption and photoluminescence) were carefully investigated, providing insights into the structure (composition)-property correlation. Furthermore, a bottom-up method was employed to construct a metal-organic framework (MOF) on the NC surface, which did not essentially alter the metal NC structure but led to the partial release of surface ligands and stimulated metal NC activity for catalyzing p-nitrophenol reduction. Furthermore, surface MOF construction enhanced NC stability and water solubility, providing another dimension for tunning NC catalytic activity by modifying MOF functional groups.

Controlled Sequential Doping of Metal Nanocluster

Atomically precise doping of metal nanoclusters provides excellent opportunities not only for subtly tailoring their properties but also for in-depth understanding of composition (structure)-property correlation of metal nanoclusters and has attracted increasing interest partly due to its significance for fundamental research and practical applications. Although single and multiple metal atom doping of metal nanoclusters (NCs) has been achieved, sequential single-to-multiple metal atom doping is still a big challenge and has not yet been reported. Herein, by introducing a second ligand, a novel multistep synthesis method was developed, controlled sequential single-to-multiple metal atom doping was successfully achieved for the first time, and three doped NCs Au25Cd1(p-MBT)17(PPh3)2, Au18Cd2(p-MBT)14(PPh3)2, and [Au19Cd3(p-MBT)18]- (p-MBTH: para-methylbenzenethiol) were obtained, including two novel NCs that were precisely characterized via mass spectrometry, single-crystal X-ray crystallography, and so forth. Furthermore, sequential doping-induced evolutions in the atomic and crystallographic structures and optical and catalytic properties of NCs were revealed.

A concise guide to chemical reactions of atomically precise noble metal nanoclusters

Nanoparticles (NPs) with atomic precision, known as nanoclusters (NCs), are an emerging field in materials science in view of their fascinating structure-property relationships. Ultrasmall noble metal NPs have molecule-like properties that make them fundamentally unique compared with their plasmonic counterparts and bulk materials. In this review, we present a comprehensive account of the chemistry of monolayer-protected atomically precise noble metal nanoclusters with a focus on the chemical reactions, their diversity, associated kinetics, and implications. To begin with, we briefly review the history of the evolution of such precision materials. Then the review explores the diverse chemistry of noble metal nanoclusters, including ligand exchange reactions, ligand-induced structural transformations, and reactions with metal ions, metal thiolates, and halocarbons. Just as molecules do, these precision materials also undergo intercluster reactions in solution. Supramolecular forces between these systems facilitate the creation of well-defined hierarchical assemblies, composites, and hybrid materials. We conclude the review with a future perspective and scope of such chemistry.

Catalytic Hydrogenation of Nitroarenes over Ag33 Nanoclusters: The Ligand Effect

Using ligand-protected metallic nanoclusters with atomic precision as catalysts and elucidating its ligand effect in the catalysis are the prerequisites to deepen the structure-catalysis relationship of nanoclusters at the molecular level. Herein, a series of Ag33 nanoclusters protected with different thiolate ligands (2-phenylethanethiol, 4-chlorobenzyl mercaptan, and 4-methoxybenzyl mercaptan as precursors) were synthesized and used as heterogeneous catalysts for the conversion of nitroarenes to arylamine with NaBH4 as reductant. The obtained nanoclusters exhibited ligand-dependent catalytic activity, with benzyl thiolate ligands distinctly superior to the phenethyl thiolate ligands. DFT calculations revealed that the ligand regulated catalytic activity of the nanoclusters was ascribed to the H-π and π-π interactions between the ligands and the substrates, owing to the presence of phenyl rings in these structures. This work highlighted the importance of the ligands on the metallic nanoclusters in catalysis and provides a strategy to regulate the catalytic activity by utilizing weak interactions between the catalysts and the substrates.

Aurozyme: A Revolutionary Nanozyme in Colitis, Switching Peroxidase-Like to Catalase-Like Activity

A therapeutic strategy that could address colitis of multiple etiologies while restoring the dysbiosis of gut microbiota is attractive. Here, Aurozyme, a novel nanomedicine comprised of gold nanoparticles (AuNPs) and glycyrrhizin (GL) with a glycol chitosan coating layer, as a promising approach for colitis, is demonstrated. The unique feature of Aurozyme is the conversion of harmful peroxidase-like activity of AuNPs to beneficial catalase-like activity due to the amine-rich environment provided by the glycol chitosan. This conversion process enables Aurozyme to oxidize the hydroxyl radicals derived from AuNP, producing water and oxygen molecules. In fact, Aurozyme effectively scavenges reactive oxygen/reactive nitrogen species (ROS/RNS) and damage-associated molecular patterns (DAMPs), which can attenuate the M1 polarization of macrophage. It exhibits prolonged adhesion to the lesion site, promoting sustained anti-inflammatory effects and restoring intestinal function in colitis-challenged mice. Additionally, it increases the abundance and diversity of beneficial probiotics, which are essential for maintaining microbial homeostasis in the gut. The work highlights the transformative potential of nanozymes for the comprehensive treatment of inflammatory disease and represents an innovative switching technology of enzyme-like activity by Aurozyme.

Total Structure, Electronic Structure and Catalytic Hydrogenation Activity of Metal-Deficient Chiral Polyhydride Cu57 Nanoclusters

Accurate identifying and in-depth understanding of the defect sites in a working nanomaterial could hinge on establishing specific defect-activity relationships. Yet, atomically precise coinage-metal nanoclusters (NCs) possessing surface vacancy defects are scarce primarily owing to challenges in the synthesis and isolation of such defective NCs. Herein we report a mixed-ligand strategy to synthesizing an intrinsically chiral and metal-deficient copper hydride-rich NC [Cu57 H20 (PET)36 (TPP)4 ]+ (Cu57 H20 ). Its total structure (including hydrides) and electronic structure are well established by combined experimental and computational results. Crystal structure reveals Cu57 H20 features a cube-like Cu8 kernel embedded in a corner-missing metal-ligand shell of Cu49 (PET)36 (TPP)4 . Single Cu vacancy defect site occurs at one corner of the shell, evocative of mono-lacunary polyoxometalates. Theoretical calculations demonstrate that the above-mentioned point vacancy causes one surface hydride exposed as an interfacial capping μ3 -H- , which is accessible in chemical reaction, as proved by deuterated experiment. Moreover, Cu57 H20 shows catalytic activity in the hydrogenation of nitroarene. The success of this work opens the way for the research on well-defined chiral metal-deficient Cu and other metal NCs, including exploring their application in asymmetrical catalysis.

Sandwich-Kernelled AgCu Nanoclusters with Golden Ratio Geometry and Promising Photothermal Efficiency

Metal nanoclusters have recently attracted extensive interest from the scientific community. However, unlike carbon-based materials and metal nanocrystals, they rarely exhibit a sheet kernel structure, probably owing to the instability caused by the high exposure of metal atoms (particularly in the relatively less noble Ag or Cu nanoclusters) in such a structure. Herein, we synthesized a novel AgCu nanocluster with a sandwich-like kernel (diameter≈0.9 nm and length≈0.25 nm) by introducing the furfuryl mercaptan ligand (FUR) and the alloying strategy. Interestingly, the kernel consists of a centered silver atom and two planar Ag10 pentacle units with completely mirrored symmetry after a rotation of 36 degrees. The two Ag10 pentacles and some extended structures show an unreported golden ratio geometry, and the two inner five-membered rings and the centered Ag atom form an unanticipated full-metal ferrocene-like structure. The featured kernel structure causes the dominant radial direction transition of excitation electrons, as determined via time-dependent density functional theory calculations, which affords the protruding absorption at 612 nm and contributes to the promising photothermal conversion efficiency of 67.6 % of the as-obtained nanocluster, having important implications for structure-property correlation and the development of nanocluser-based photothermal materials.

Ce-mediated molecular tailoring on gigantic polyoxometalate {Mo132} into half-closed {Ce11Mo96} for high proton conduction

Precise synthesis of polyoxometalates (POMs) is important for the fundamental understanding of the relationship between the structure and function of each building motif. However, it is a great challenge to realize the atomic-level tailoring of specific sites in POMs without altering the major framework. Herein, we report the case of Ce-mediated molecular tailoring on gigantic {Mo132}, which has a closed structural motif involving a never seen {Mo110} decamer. Such capped wheel {Mo132} undergoes a quasi-isomerism with known {Mo132} ball displaying different optical behaviors. Experiencing an 'Inner-On-Outer' binding process with the substituent of {Mo2} reactive sites in {Mo132}, the site-specific Ce ions drive the dissociation of {Mo2*} clipping sites and finally give rise to a predictable half-closed product {Ce11Mo96}. By virtue of the tailor-made open cavity, the {Ce11Mo96} achieves high proton conduction, nearly two orders of magnitude than that of {Mo132}. This work offers a significant step toward the controllable assembly of POM clusters through a Ce-mediated molecular tailoring process for desirable properties.

Counteranion-induced structural isomerization of phosphine-protected PdAu8 and PtAu8 clusters

Controlling the geometric structures of metal clusters through structural isomerization allows for tuning of their electronic state. In this study, we successfully synthesized butterfly-motif [PdAu₈(PPh₃)₈]²⁺ (PdAu8-B, B means butterfly-motif) and [PtAu₈(PPh₃)₈]²⁺ (PtAu8-B) by the structural isomerization from crown-motif [PdAu₈(PPh₃)₈]²⁺ (PdAu8-C, C means crown-motif) and [PtAu₈(PPh₃)₈]²⁺ (PtAu8-C), induced by association with anionic polyoxometalate, [Mo₆O₁₉]^2- (Mo6) respectively, whereas their structural isomerization was suppressed by the use of [NO₃]^- and [PMo₁₂O₄₀]^3- as counter anions. DR-UV-vis-NIR and XAFS analyses and density functional theory calculations revealed that the synthesized [PdAu₈(PPh₃)₈][Mo₆O₁₉] (PdAu8-Mo6) and [PtAu₈(PPh₃)₈][Mo₆O₁₉] (PtAu8-Mo6) had PdAu8-B and PtAu8-B respectively because PdAu8-Mo6 and PtAu8-Mo6 had bands in optical absorption at the longer wavelength region and different structural parameters characteristic of the butterfly-motif structure obtained by XAFS analysis. Single-crystal and powder X-ray diffraction analyses revealed that PdAu8-B and PtAu8-B were surrounded by six Mo6 with rock salt-type packing, which stabilizes the semi-stable butterfly-motif structure to overcome high activation energy for structural isomerization.

Programmable kernel structures of atomically precise metal nanoclusters for tailoring catalytic properties

The unclear structures and polydispersity of metal nanoparticles (NPs) seriously hamper the identification of the active sites and the construction of structure-reactivity relationships. Fortunately, ligand-protected metal nanoclusters (NCs) with atomically precise structures and monodispersity have become an ideal candidate for understanding the well-defined correlations between structure and catalytic property at an atomic level. The programmable kernel structures of atomically precise metal NCs provide a fantastic chance to modulate their size, shape, atomic arrangement, and electron state by the precise modulating of the number, type, and location of metal atoms. Thus, the special focus of this review highlights the most recent process in tailoring the catalytic activity and selectivity over metal NCs by precisely controlling their kernel structures. This review is expected to shed light on the in-depth understanding of metal NCs' kernel structures and reactivity relationships.

Impact of the metal core on the electrochemiluminescence of a pair of atomically precise Au20 nanocluster isomers

Although the electrochemiluminescence (ECL) of metal nanoclusters has been reported, revealing the correlation between structure and ECL at an atomic level is highly challenging. Here, we reported the impact of the metal core of Au₂₀(SAdm)₁₂(CHT)₄ (Au₂₀-AC for short; SAdm = 1-adamantanethiolate; CHT= cyclohexanethiol) and its isomer Au₂₀(TBBT)₁₆ (TBBT = 4-tert-butylthiophenol) on their solution-state and solid-state electrochemiluminescence. In self-annihilation ECL experiments, Au₂₀-AC showed a strong cathodic ECL but a weak anodic ECL, while the ECL signal of Au₂₀(TBBT)₁₆ was weak and barely detectable. Density functional theory (DFT) calculations showed that the Au₇ kernel of [Au₂₀-AC]^- is metastable, weakening its anodic ECL. Au₂₀-AC in solution-state displayed an intense co-reactant ECL in the near-infrared region, which is 7 times higher than that of standard Ru(bpy)₃²⁺. The strongest solid-state ECL emissions of Au₂₀-AC and Au₂₀(TBBT)₁₆ were at 860 and 770 nm, respectively - 15 nm red-shifted for Au₂₀-AC and 20 nm blue-shifted for Au₂₀(TBBT)₁₆, compared to their corresponding solid-state photoluminescence (PL) emissions. This work shows that ECL is significantly affected by the subtle differences of the metal core, and offers a potential basis for sensing and immunoassay platforms based on atomically precise emissive metal nanoclusters.

Enhanced Antibacterial Activity of Novel Fluorescent Glutathione-Capped Ag Nanoclusters

Ag nanomaterials are promising candidates for the discovery of next-generation antibiotics with a high antibacterial effect against multi-drug resistant strains. This paper reports a simple synthesis of novel water-soluble glutathione-capped silver nanoclusters (GSH-Ag NCs) with an enhanced antibacterial activity. According to thin layer chromatography (TLC), the synthesized GSH-Ag NCs are an individual fraction of the same composition without any impurities. According to matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) and energy dispersive X-ray (EDX) analyses, the silver core of the GSH-Ag NCs contains approximately 35 silver atoms, and the molecular weight of these nanoclusters is about 11 kDa. The fabricated silver nanoclusters have a reddish fluorescence (λex/λem = 509/645 nm), with a large Stokes shift (>130 nm), and ultra-small size (less than 2 nm) according to transmission electron microscopy (TEM) data and dynamic light scattering (DLS) analysis. The antibacterial activity and minimal inhibitory concentrations of the silver nanoclusters towards Escherichia coli, Staphylococcus aureus, Bacillus cereus and Enterobacter cloacae were evaluated using the agar well-diffusion method and resazurin metabolism assay. The antibacterial activity of chelated silver in the nanoclusters was found to be significantly higher compared to the activity of free silver ions. To explain the possible mechanisms underlying the antibacterial actions of the GSH-Ag nanoclusters, molecular docking was performed, and prospective bacterial targets were identified using AutoDock.

Direct and Indirect Pathways of CdTeSe Magic-Size Cluster Isomerization Induced by Surface Ligands at Room Temperature

The field of isomerization reactions for colloidal semiconductor magic-size clusters (MSCs) remains largely unexplored. Here, we show that MSCs isomerize via two fundamental pathways that are regulated by the acidity and amount of an incoming ligand, with CdTeSe as the model system. When MSC-399 isomerizes to MSC-422 at room temperature, the peak red-shift from 399 to 422 nm is continuous (pathway 1) and/or stepwise (pathway 2) as monitored in situ and in real time by optical absorption spectroscopy. We propose that pathway 1 is direct, with intracluster configuration changes and a relatively large energy barrier. Pathway 2 is indirect, assisted by the MSC precursor compounds (PCs), from MSC-399 to PC-399 to PC-422 to MSC-422. Pathway 1 is activated when PC-422 to MSC-422 is suppressed. Our findings unambiguously suggest that when a change occurs directly on a nanospecies, its absorption peak continuously shifts. The present study provides an in-depth understanding of the transformative behavior of MSCs via ligand-induced isomerization upon external chemical stimuli.

Self-isomerization of nearly planar superatoms formed by actinide embedded gold clusters

First-principles calculations show a self-isomerization process of the nearly planar superatom, in which the maximum energy difference between different extreme points is below 0.1 eV and a crossing between singlet and triplet states is also involved. Further UV-Vis spectra reveal a correlation between the spectra and structures caused by self-isomerization.

From Au11 to Au13: Tailored Synthesis of Superatomic Di-NHC/PPh3-Stabilized Molecular Gold Nanoclusters

Herein, we report a new method to synthesize molecular gold nanoclusters (AuNCs) stabilized by phosphine (PR₃) and di-N-heterocyclic carbene (di-NHC) ligands. The interaction of di-NHC gold(I) complexes, with the general formula [(di-NHC)Au₂Cl₂] with well-known [Au₁₁(PPh₃)₈Cl₂]Cl clusters provides three new classes of AuNCs through a controllable reaction sequence. The synthesis involves an initial ligand metathesis reaction to produce [Au₁₁(di-NHC)(PPh₃)₆Cl₂]⁺ (type 1 clusters), followed by a thermally induced rearrangement/metal complex addition with the formation of Au₁₃ clusters [Au₁₃(di-NHC)₂(PPh₃)₄Cl₄]⁺ (type 2 clusters). Finally, an additional metathesis process yields [Au₁₃(di-NHC)₃(PPh₃)₃Cl₃]²⁺ (type 3 clusters). The electronic and steric properties of the employed di-NHC ligand affect the product distribution, leading to the isolation and full characterization of different clusters as the main product. A type 3 cluster has been also structurally characterized and was preliminarily found to be strongly emissive in solution.

Direct Observation of the Pressure-Induced Structural Variation in Gold Nanoclusters and the Correlated Optical Response

The ability to gradually modify the atomic structures of nanomaterials and directly identify such structural variation is important in nanoscience research. Here, we present the first example of a high-pressure single-crystal X-ray diffraction analysis of atomically precise metal nanoclusters. The pressure-dependent, subangstrom structural evolution of an ultrasmall gold nanoparticle, Au₂₅S₁₈, has been directly identified. We found that a 0.1 Å decrease of the Au-Au bond length could induce a blue-shift of 30 nm in the photoluminescence spectra of gold nanoclusters. From theoretical calculations, the origins of the blue-shift and enhanced photoluminescence under pressure are investigated, which are ascribed to molecular orbital symmetry and conformational locking, respectively. The combination of the high-pressure in situ X-ray results with both theoretical and experimental optical spectra provides a direct and generalizable avenue to unveil the underlying structure-property relations for nanoclusters and nanoparticles which cannot be obtained through traditional physical chemistry measurements.

Assembly-induced spin transfer and distance-dependent spin coupling in atomically precise AgCu nanoclusters

Nanoparticle assembly paves the way for unanticipated properties and applications from the nanoscale to the macroscopic world. However, the study of such material systems is greatly inhibited due to the obscure compositions and structures of nanoparticles (especially the surface structures). The assembly of atomically precise nanoparticles is challenging, and such an assembly of nanoparticles with metal core sizes strictly larger than 1 nm has not been achieved yet. Here, we introduced an on-site synthesis-and-assembly strategy, and successfully obtained a straight-chain assembly structure consisting of Ag₇₇Cu₂₂(CHT)₄₈ (CHT: cyclohexanethiolate) nanoparticles with two nanoparticles separated by one S atom, as revealed by mass spectrometry and single crystal X-ray crystallography. Although Ag₇₇Cu₂₂(CHT)₄₈ bears one unpaired shell-closing electron, the magnetic moment is found to be mainly localized at the S linker with magnetic isotropy, and the sulfur radicals were experimentally verified and found to be unstable after disassembly, demonstrating assembly-induced spin transfer. Besides, spin nanoparticles are found to couple and lose their paramagnetism at sufficiently short inter-nanoparticle distance, namely, the spin coupling depends on the inter-nanoparticle distance. However, it is not found that the spin coupling leads to the nanoparticle growth.

The assembly of atomically precise clusters into ordered superstructures enables new functional material designs. Here, the authors propose a strategy for linear arrangements of AgCu clusters and explore the consequent transfer and coupling of magnetic spins.

Co-reactant-Free Transformation in Atomically Precise Metal Nanoclusters

Transformation chemistry has advanced significantly in recent years as an excellent methodology for synthesizing new nanoclusters and functionalizing the existing ones. However, rational synthesis and fundamental understanding of the structural evolution among clusters have not yet been achieved in nanocluster science. A deeper understanding of the fundamental aspects of structure-property correlation is necessary for the employment of befitting nanoclusters for specific applications. Very recently, the transformation of nanoclusters without the use of conventional co-reactants has been brought to light. These co-reactant-less transformations are triggered by various conditions, such as pH, solvent, light, temperature, etc. In this perspective, we discuss how this unique method of transformation without any co-reactant benefits the basic understanding of growth patterns and the corresponding property evolution in nanoclusters.

Structural Prediction of Anion Thiolate Protected Gold Clusters of [Au28+7n(SR)17+3n]− (n = 0-4)

Structural prediction of thiolate-protected gold nanocluster (AuNCs) with diverse charge states can enrich the understanding of this species. Till now, most expementally synthesized or theoretically predicted AuNCs structures own neutral total charge. In this work, a series of gold nanoclusters with negative total charge including [Au28(SR)17]−, [Au35(SR)20]−, [Au42(SR)23]−, [Au49(SR)26]−, and [Au56(SR)29]− are designed. Following crystallized [Au23(SR)16]- prototype structure, the inner core of the newly predicted clusters are obtained through packing crossed Au7. Next, proper protecting thiolate ligands are arranged to fullfil the duet rule to obtain Au3(2e) and Au4(2e). Extensive analysis indicates these cluster own high stabilities. Molecular orbital analysis shows that the orbitals for the populations of the valence electron locate at each Au3(2e) and Au4(2e), which demonstrates the reliability the GUM model. This work should be helpful for enriching the structural diversity of AuNCs.

Effect of Ligands on the Stability of Gold Nanoclusters

Gold nanoclusters (AuNCs) are atomic architectures that can be precisely tailored for catalytic applications. In this work, we studied two benchmark AuNCs, Au₂₅(SR)₁₈ and Au₁₄₄(SR)₆₀, covered by aromatic and aliphatic ligands to envision how the 3D structure of the ligand impacts the stability of the nanomaterial. Surprisingly, we found that increasing the alkanethiol length has a poor or null effect on the stability of the AuNCs, a trend opposite to that on Au(111) surfaces. When considering the aromatic or aliphatic nature, the AuNC stability follows the same trend as on Au(111): the thermodynamical stability is dictated by the ligand density rather than its chemical nature, where the aliphatic ligand imparts more stability than the aromatic one. Our findings provide a tool to predict how an ultrasmall gold core can interact with the environment, substrate, and themselves according to the stability of its protecting ligand shell.

Identification of the Active Species in Bimetallic Cluster Catalyzed Hydrogenation

Identification of the authentic active species of cluster catalysis is rather challenging, and direct structural evidence is quite valuable and difficult to obtain. Two "isostructural" clusters, Ag₂₅Cu₄Cl₆(dppb)₆(PhC≡C)₁₂(SO₃CF₃)₃ (1) and Ag₂₅Cu₄Cl₆H₈(dppb)₆(PhC≡C)₁₂(SO₃CF₃)₃ (2_H) (dppb is 1,4-bis(diphenylphosphine)butane), have been successfully isolated and structurally characterized. Both these clusters have a centered icosahedron Ag₁₃ core with the same peripheral composition and structure. The only difference is that 2_H has eight hydrides but 1 has none, that is, the kernels are Ag₁₃⁵⁺ and Ag₁₃H₈⁵⁺ in 1 and 2_H, respectively. The catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) as a model reaction is assessed with the two clusters. Cluster 2_H is very active with 100% yield within 2 h, whereas 1 shows a very low conversion (∼8%) under the same conditions. Interestingly, high catalytic activity was observed when 1 was converted to 2_H with the oxidation of H₂O₂ under catalytic conditions. The unprecedented transformation of a reduced nanocluster to an Ag(I)Cu(I) bimetallic cluster compound provides an excellent platform to determine the real active cluster in terms of metal cluster catalysis. The present work presents clear structural evidence that the catalytic performance of metal nanoclusters can be modulated by properly regulating the oxidation state of their constituted metal atoms.

Solvent-Induced Isomeric Cu13 Nanoclusters: Chlorine to Copper Charge Transfer Boosting Molecular Oxygen Activation in Sulfide Selective Oxidation

Isomers with minimal structural dissimilarities are promising research objects to obtain a comprehensive understanding of structure-property relationships; however, comparability of isomeric structures is a prerequisite. Herein, two quasi-structurally isomeric 13-nuclei copper nanoclusters (Cu NCs) (Cu13a and Cu13b) containing highly similar Cu₁₃ kernels and different arrangements of peripheral ligands were obtained using a solvent-induced strategy. The exotic chloride ion is shown to play a prominent role in inducing the selective formation of two quasi-isomers, where the comparative study to establish a structure-property relationship was realized. Due to the charge transition from chlorine to the copper core (X_(Cl)M_(Cu)CT), the molecular oxygen activation of Cu13a showed higher singlet oxygen (¹O₂) and lower superoxide radical (O₂^•-) yields compared to those of Cu13b, which gives it better catalytic selectivity for the ¹O₂ involved selective oxidation of sulfides. The present work not only offers a controllable strategy for the rational design and synthesis of quasi-structurally isomeric Cu NCs but also provides a pathway to boost catalytic selectivity by a halogen to metal core charge transition.

New structural insights into the stability of Au22(SR)16 nanocluster under ring model guidance

This study presents thorough structural insights into the stability of crystallized Au₂₂(SAdm)₁₆ (HSAdm = 1-adamantanethiol) nanocluster. With the recently developed Ring Model for describing the interaction between inner gold cores and outer protecting ligands in thiolate-protected gold nanoclusters, the experimental spontaneous transformation from the crystallized Au₂₂(SAdm)₁₆ to Au₂₁(SAdm)₁₅ could be well understood as structurally unfavorable for the current Au₂₂(SAdm)₁₆ and could also be attributed to the weaker aurophilic interaction between the inner Au₄ core and the surrounding rings in Au₂₂(SAdm)₁₆ over that in Au₂₁(SAdm)₁₅. Furthermore, with the Ring Model and the grand unified model, two new Au₂₂(SCH₃)₁₆ isomers with evident lower energies, higher HOMO-LUMO gaps as well as distinct optical properties over the available crystallized isomer were obtained. This study deepens the current knowledge on the structure of the Au₂₂(SR)₁₆ cluster from a new structural point of view and also confirms the validity as well as practicability of the Ring Model in understanding and predicting the stable structures of thiolate-protected gold nanoclusters.

Bis-Schiff base linkage-triggered highly bright luminescence of gold nanoclusters in aqueous solution at the single-cluster level

Metal nanoclusters (NCs) have been developed as a new class of luminescent nanomaterials with potential applications in various fields. However, for most of the metal NCs reported so far, the relatively low photoluminescence quantum yield (QY) in aqueous solution hinders their applications. Here, we describe the utilization of bis-Schiff base linkages to restrict intramolecular motion of surface motifs at the single-cluster level. Based on Au₂₂(SG)₁₈ (SG: glutathione) NCs, an intracluster cross-linking system was constructed with 2,6-pyridinedicarboxaldehyde (PDA), and water-soluble gold NCs with luminescence QY up to 48% were obtained. The proposed approach for achieving high emission efficiency can be extended to other luminescent gold NCs with core-shell structure. Our results also show that the content of surface-bound Au(I)-SG complexes has a significant impact on the PDA-induced luminescence enhancement, and a high ratio of Au(I)-SG will be beneficial to increasing the photoluminescence intensity of gold NCs.

Boosting the luminescence of atomically precise metal clusters is a main goal in view of applications. Here, the authors describe a strategy to increase the photoluminescence quantum yield of water-soluble gold clusters at the single-cluster level via formation of bis-Schiff base linkages, providing detailed insight into the mechanism.

Insight into the Mechanism of Single-Metal-Atom Tailoring on the Surface of Au-Cu Alloy Nanoclusters

Tailoring the surface structure of nanomaterials is desirable for investigating their mechanisms and properties from a nanochemistry perspective. The modification of the surface of metal nanoparticles with a single metal atom has proven difficult, which has hindered the understanding of the contribution of different motifs in nanoclusters to their properties. Herein, we report single-metal-atom surface tailoring by thermally etching the nanocluster Au_xCu_15-x(DPPMH)₃(SPhCl₂)₉ (x = 8 or 9) to obtain Au_xCu_16-x(DPPMH)₂(DPPM)(SPhCl₂)₉ (x = 9 or 10) nanoclusters. An Au₇Cu₄ core was observed in both nanoclusters, which can be regarded as part of an icosahedron. Experiments and theoretical simulations revealed the tailoring processes of the icosahedron. Both nanoclusters displayed an NIR-II emission, and the introduction of the surface metal atom led to a red-shift in the emission band from 983 to 1025 nm. This work contributes to the development of precisely tailored nanocluster structures and provides an understanding of structure-property correlations.

Master key to coinage metal nanoclusters treasure chest: 38-metal clusters

Atomically precise metal nanoclusters with specific chemical compositions have become a popular research topic due to their precise structures, attractive properties, and wide range of applications in various fields. Currently, among more than 100 reported metal nanoclusters with precise formulas, 38-atom coinage metal nanoclusters stand out due to their unique structural diversities, such as face-centered cubic (FCC) and body-centered cubic (BCC) arrangements. Among them, the formation of the metal cores includes vertex-sharing, face-fusion, and FCC cubes fusion. Due to their geometrical features, 38-atom coinage metal nanoclusters exhibit attractive properties, making them an ideal model for exploring structure-property relationships. Therefore, 38-atom coinage metal nanoclusters are a universal key to the treasure trove of nanoclusters, which can open almost all fields and are of great research significance. This paper focuses on the structure of 38-atom coinage metal nanoclusters and reviews the preparation and crystallization methods, excellent properties, and practical applications. Finally, future research prospects and development opportunities are provided.

Plasmons: untangling the classical, experimental, and quantum mechanical definitions

Plasmons have been widely studied over the past several decades because of their ability to strongly absorb light and localize its electric field on the nanoscale, leading to applications in spectroscopy, biosensing, and solar energy storage. In a classical electrodynamics framework, a plasmon is defined as a collective, coherent oscillation of the conduction electrons of the material. In recent years, it has been shown experimentally that noble metal nanoclusters as small as a few nm can support plasmons. This work has led to numerous attempts to identify plasmons from a quantum mechanical perspective, including many overlapping and sometimes conflicting criteria for plasmons. Here, we shed light on the definitions of plasmons. We start with a brief overview of the well-established classical electrodynamics definition of a plasmon. We then turn to the experimental features used to determine whether a particular system is plasmonic, connecting the experimental results to the corresponding features of the classical electrodynamics description. The core of this article explains the many quantum mechanical criteria for plasmons. We explore the common features that these criteria share and explain how these features relate to the classical electrodynamics and experimental definitions. This comparison shows where more work is needed to expand and refine the quantum mechanical definitions of plasmons.

D–π–A type conjugated indandione derivatives: ultrafast broadband nonlinear absorption responses and transient dynamics

The ultrafast nonlinear optical response of two 1,3-indandione derivatives (INB3 and INT3) was systematically investigated by the femtosecond Z-scan and pump-probe technique at multiple visible and near infrared wavelengths. Both compounds show strong broadband nonlinear absorption (NLA) and different wavelength-dependent two-photon absorption (TPA) characteristics in the range of 650–1100 nm. The TPA cross section of trithiophene-based compound INT3 was found to be larger than that of triphenylamine-based compound INB3 in the red region (650–800 nm), which is attributed to its longer π-conjugated structure and better molecular planarity. Interestingly, the effective NLA of INB3 was found to be larger than INT3 in the NIR region (800–1100 nm), which is related to the excited state absorption (ESA) induced by TPA. The ultrafast dynamics of both compounds were investigated by femtosecond transient absorption spectroscopy, which revealed a broadband ESA including several relaxation processes. This work extends nonlinear optical research on indandione derivatives, and the results suggest that these derivatives are promising candidates for optical limiting applications.

In the red region (650–800 nm), the nonlinear absorption of trithiophene-based compound INT3 is greater than that of triphenylamine-based compound INB3, while in the NIR region (800–1100 nm), the strength of nonlinear absorption is the opposite.

Identifying Highly Photoelectrochemical Active Sites of Two Au21 Nanocluster Isomers toward Bright Near-Infrared Electrochemiluminescence

Thus far, no correlation between nanocluster structures and their electrochemiluminescence (ECL) has been identified. Herein, we report how face-centered-cubic and hexagonal close-packed structures of two Au₂₁(SR)₁₅ nanocluster isomers determine their chemical reactivity. The relationships were explored by means of ECL and photoluminescence spectroscopy. Both isomers reveal unprecedented ECL efficiencies in the near-infrared region, which are >10- and 270-fold higher than that of standard Ru(bpy)₃²⁺, respectively. Photoelectrochemical reactivity as well as ECL mechanisms were elucidated based on electrochemistry, spooling photoluminescence, and ECL spectroscopy, unfolding the three emission enhancement origins: (i) effectively exposed reactive facets available to undergo electron transfer reactions; (ii) individual excited-state regeneration loops; (iii) cascade generations of various exited states. Indeed, these discoveries will have immediate impacts on various applications including but not limited to single molecular detection as well as photochemistry and electrocatalysis toward clean photon-electron conversion processes such as light-harvesting and light-emitting technologies.