Crystal Structure of Barrel-Shaped Chiral Au130(p-MBT)50 Nanocluster

Molecular Interactions in Atomically Precise Metal Nanoclusters

For nanochemistry, precise manipulation of nanoscale structures and the accompanying chemical properties at atomic precision is one of the greatest challenges today. The scientific community strives to develop and design customized nanomaterials, while molecular interactions often serve as key tools or probes for this atomically precise undertaking. In this Perspective, metal nanoclusters, especially gold nanoclusters, serve as a good platform for understanding such nanoscale interactions. These nanoclusters often have a core size of about 2 nm, a defined number of core metal atoms, and protecting ligands with known crystal structure. The atomically precise structure of metal nanoclusters allows us to discuss how the molecular interactions facilitate the systematic modification and functionalization of nanoclusters from their inner core, through the ligand shell, to the external assembly. Interestingly, the atomic packing structure of the nanocluster core can be affected by forces on the surface. After discussing the core structure, we examine various atomic-level strategies to enhance their photoluminescent quantum yield and improve nanoclusters' catalytic performance. Beyond the single cluster level, various attractive or repulsive molecular interactions have been employed to engineer the self-assembly behavior and thus packing morphology of metal nanoclusters. The methodological and fundamental insights systemized in this review should be useful for customizing the cluster structure and assembly patterns at the atomic level.

Single-atom alloy structure and unique bonding properties of Au104Ag40(PET)60 nanoclusters

The detailed characterization of AuAg alloy nanoclusters is essential to guide the discovery of species ideal for applications in various fields including catalysis and biomedicine. This work presents structural analysis of the Au104Ag40(PET)60 species through X-ray absorption spectroscopy (XAS). First, XAS fitting is utilized to model the distribution of Au and Ag atoms within the structure. Our proposed model assigns Ag atoms to the vertex sites of the second shell of the metal core, as well as the outermost staple sites. This distribution reveals Au104Ag40(PET)60 to be a Ag single-atom alloy. The proposed model shows outstanding agreement with the coordination number values derived from XAS. XAS near-edge analysis is employed to investigate the alloy bonding interactions between Au and Ag. Substantial d-electron transfer from Au to Ag is observed in this sample, beyond the magnitude of previously studied AuAg NCs. This work enhances the understanding of the structure-property relationship of AuAg alloy NCs, offering insights which can be applied to other large NCs and even NPs. These insights will in turn aid the discovery of new materials for use in various applications.

'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.

Chiral Inversion of Au40(SR)24 Nanocluster Driven by Rotation of Gold Tetrahedra in the Kekulé-like Core

Studying the chiral characteristics and chiral inversion mechanisms of gold nanoclusters is important to promote their applications in the field of chiral catalysis and chiral recognition. Herein, we investigated the chiral inversion process of the Au40(SR)24 nanocluster and its derivatives using density functional theory calculations. The results showed that the chiral inversion process can be achieved by rotation of tetrahedra units in the gold core without breaking the Au-S bond. This work found that Au40 nanoclusters protected by different ligands have different chiral inversion mechanisms, and the difference is mainly attributable to the steric effects of the ligands. Moreover, the chiral inversion of the derivative clusters (Au34, Au28, and Au22) of the Au40 nanocluster can also be accomplished by the rotation of the Au4 tetrahedra units in the gold core. The energy barrier in the chiral inversion process of gold nanoclusters increases with the decrease of Au4 tetrahedra units in the gold core. This work identifies a chiral inversion mechanism with lower reaction energy barriers and provided a theoretical basis for the study of gold nanocluster chirality.

Evolution of the atomic and electronic structures of CuO clusters: a comprehensive study using the DFT approach

One of the most fundamental aspects of cluster science is to understand the structural evolution at the atomic scale. In this connection, here we report a comprehensive study of the atomic and electronic structures of (CuO)n clusters for n = 1 to 12 using DFT-based formalisms. Both the plane wave-based pseudo-potential approach and LCAO-MO-based method have been employed to obtain the ground state geometries of neutral, cation and anion copper oxide clusters. The results reveal that neutral copper oxide clusters favor a planar ring structure up to heptamer and from octamer onwards they adopt a three-dimensional motif with (CuO)9 and (CuO)12 forming a barrel-shaped layered structure. Detailed electronic structure analysis reveals that the transition of the atomic structure from 2D to 3D is guided by the energy balance of the Cu-O (d-p) and Cu-Cu (d-d) bonds. The removal of one electron from the cluster (cation) results in slightly stretched bonds while the addition of one electron (anion) showed compression in the overall geometries. The thermodynamic and electronic stability of these clusters has been analyzed by estimating their binding energy, ionization energy and electron affinity as a function of size. Remarkably, among these clusters, the octamer (CuO)8 and dodecamer (CuO)12 show higher binding energy and electron affinity (∼6.5 eV) with lower ionization energy (5.5-6.0 eV). This unique feature of the octamer and dodecamer indicates that they are very promising candidates for both oxidizing and reducing agents in different important chemical reactions.

Eight-Electron Superatomic Cu31 Nanocluster with Chiral Kernel and NIR-II Emission

Owing to the inherent instability caused by the low Cu(I)/Cu(0) half-cell reduction potential, Cu(0)-containing copper nanoclusters are quite uncommon in comparison to their Ag and Au congeners. Here, a novel eight-electron superatomic copper nanocluster [Cu₃₁(4-MeO-PhC≡C)₂₁(dppe)₃](ClO₄)₂ (Cu₃₁, dppe = 1,2-bis(diphenylphosphino)ethane) is presented with total structural characterization. The structural determination reveals that Cu₃₁ features an inherent chiral metal core arising from the helical arrangement of two sets of three Cu₂ units encircling the icosahedral Cu₁₃ core, which is further shielded by 4-MeO-PhC≡C^- and dppe ligands. Cu₃₁ is the first copper nanocluster carrying eight free electrons, which is further corroborated by electrospray ionization mass spectrometry, X-ray photoelectron spectroscopy and density functional theory calculations. Interestingly, Cu₃₁ demonstrates the first near-infrared (750-950 nm, NIR-I) window absorption and the second near-infrared (1000-1700 nm, NIR-II) window emission, which is exceptional in the copper nanocluster family and endows it with great potential in biological applications. Of note, the 4-methoxy groups providing close contacts with neighboring clusters are crucial for the cluster formation and crystallization, while 2-methoxyphenylacetylene leads only to copper hydride clusters, Cu₆H or Cu₃₂H₁₄. This research not only showcases a new member of copper superatoms but also exemplifies that copper nanoclusters, which are nonluminous in the visible range may emit luminescence in the deep NIR region.

Atomically precise gold nanoclusters at the molecular-to-metallic transition with intrinsic chirality from surface layers

The advances in determining the total structure of atomically precise metal nanoclusters have prompted extensive exploration into the origins of chirality in nanoscale systems. While chirality is generally transferrable from the surface layer to the metal-ligand interface and kernel, we present here an alternative type of gold nanoclusters (138 gold core atoms with 48 2,4-dimethylbenzenethiolate surface ligands) whose inner structures are not asymmetrically induced by chiral patterns of the outermost aromatic substituents. This phenomenon can be explained by the highly dynamic behaviors of aromatic rings in the thiolates assembled via π - π stacking and C - H···π interactions. In addition to being a thiolate-protected nanocluster with uncoordinated surface gold atoms, the reported Au₁₃₈ motif expands the size range of gold nanoclusters having both molecular and metallic properties. Our current work introduces an important class of nanoclusters with intrinsic chirality from surface layers rather than inner structures and will aid in elucidating the transition of gold nanoclusters from their molecular to metallic states.

Size Effects of Atomically Precise Gold Nanoclusters in Catalysis

The emergence of ligand-protected, atomically precise gold nanoclusters (NCs) in recent years has attracted broad interest in catalysis due to their well-defined atomic structures and intriguing properties. Especially, the precise formulas of NCs provide an opportunity to study the size effects at the atomic level without complications by the polydispersity in conventional nanoparticles that obscures the relationship between the size/structure and properties. Herein, we summarize the catalytic size effects of atomically precise, thioate-protected gold NCs in the range of tens to hundreds of metal atoms. The catalytic reactions include electrochemical catalysis, photocatalysis, and thermocatalysis. With the precise sizes and structures, the fundamentals underlying the size effects are analyzed, such as the surface area, electronic properties, and active sites. In the catalytic reactions, one or more factors may exert catalytic effects simultaneously, hence leading to different catalytic-activity trends with the size change of NCs. The summary of literature work disentangles the underlying fundamental mechanisms and provides insights into the size effects. Future studies will lead to further understanding of the size effects and shed light on the catalytic active sites and ultimately promote catalyst design at the atomic level.

Platonic and Archimedean solids in discrete metal-containing clusters

Metal-containing clusters have attracted increasing attention over the past 2-3 decades. This intense interest can be attributed to the fact that these discrete metal aggregates, whose atomically precise structures are resolved by single-crystal X-ray diffraction (SCXRD), often possess intriguing geometrical features (high symmetry, aesthetically pleasing shapes and architectures) and fascinating physical properties, providing invaluable opportunities for the intersection of different disciplines including chemistry, physics, mathematical geometry and materials science. In this review, we attempt to reinterpret and connect these fascinating clusters from the perspective of Platonic and Archimedean solid characteristics, focusing on highly symmetrical and complex metal-containing (metal = Al, Ti, V, Mo, W, U, Mn, Fe, Co, Ni, Pd, Pt, Cu, Ag, Au, lanthanoids (Ln), and actinoids) high-nuclearity clusters, including metal-oxo/hydroxide/chalcogenide clusters and metal clusters (with metal-metal binding) protected by surface organic ligands, such as thiolate, phosphine, alkynyl, carbonyl and nitrogen/oxygen donor ligands. Furthermore, we present the symmetrical beauty of metal cluster structures and the geometrical similarity of different types of clusters and provide a large number of examples to show how to accurately describe the metal clusters from the perspective of highly symmetrical polyhedra. Finally, knowledge and further insights into the design and synthesis of unknown metal clusters are put forward by summarizing these "star" molecules.

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.

Face-Centered Cubic Silver Nanoclusters Consolidated with Tetradentate Formamidinate Ligands

Growing attention has been paid to nanoclusters with face-centered cubic (fcc) metal kernels, due to its structural similarity to bulk metals. We demonstrate that the use of tetradentate formamidinate ligands facilitate the construction of two fcc silver nanoclusters: [Ag₅₂(5-F-dpf)₁₆Cl₄](SbF₆)₂ (Ag₅₂, 5-F-Hdpf = N,N'-di(5-fluoro-2-pyridinyl)formamidine) and [Ag₅₃(5-Me-dpf)₁₈](NO₃)₅ (Ag₅₃, 5-Me-Hdpf = N,N'-di(5-methyl-2-pyridinyl)formamidine). Single-crystal X-ray structural analysis revealed that the silver atoms in both clusters are in a layer-by-layer arrangement, which can be viewed as a portion of the fcc packing of silver. The nitrogen donors of amidinate ligands selectively passivate the {111} facets. All silver atoms are involved in the fcc packing, that is, no staple motifs are observed due to the linear arrangement of the four N donors of the dpf ligands. The characteristic optical absorption bands of Ag₅₂ and Ag₅₃ have been studied with a time-dependent density functional theory. This work provides a facile access to assembling atomically precise fcc-type nanoclusters and shows the prospect of amidinates as protecting ligands in synthesizing metal nanoclusters.

Understanding a ligand's effects on intra-cluster and inter-cluster assembly

Ligands play an essential role in cluster assembly; however, understanding this behavior at the atomic level is far off. In this work, Cd₁₂Ag₃₂(S-PhOMe)₃₆(PPh)₄@Cd₆Ag₂(S-PhOMe)₆Cl₆(PPh₃)₈@Ag₆(S-PhOMe)₆Cl₂ (Abbrev. Cd12Ag32-1) and Cd₁₂Ag₃₂(S-c-C₆H₁₁)₃₆ (Abbrev. Cd12Ag32-2) were synthesized and structurally determined by single-crystal X-ray diffraction. An important finding is the selective adsorption of phosphine ligands that is caused by the different types of thiol ligands. In addition, Cd12Ag32-1 follows a unique stacking pattern in a superlattice with multiple inter-cluster channels. Overall, this study is helpful for an in-depth understanding of the effect of mixed ligands on nanocluster formation and the correlation between structure and properties in the nanocluster range.

Interactions of Metal Nanoclusters with Light: Fundamentals and Applications

The interactions of materials with light determine their applications in various fields. In the past decade, ultrasmall metal nanoclusters (NCs) have emerged as a promising class of optical materials due to their unique molecular-like properties. Herein, the basic principles of optical absorption and photoluminescence of metal NCs, their interactions with polarized light, and light-induced chemical reactions, are discussed, highlighting the roles of the core and protecting ligands/motifs of metal NCs in their interactions with light. The metal core and protecting ligands/motifs determine the electronic structures of metal NCs, which are closely related to their optical properties. In addition, the protecting ligands/motifs of metal NCs contribute to their photoluminescence and chiral origin, further promoting the interactions of metal NCs with light through various pathways. The fundamentals of light-NC interactions provide guidance for the design of metal NCs in optical applications, which are discussed in the second part. In the last section, some strategies are proposed to further understand light-NC interactions, highlighting the challenges and opportunities. It is hoped that this work will stimulate more research on the optical properties of metal NCs and their applications in various fields.

Site-specific doping of silver atoms into a Au25 nanocluster as directed by ligand binding preferences

For the first time site-specific doping of silver into a spherical Au25 nanocluster has been achieved in [Au19Ag6(MeOPhS)17(PPh3)6] (BF4)2 (Au19Ag6) through a dual-ligand coordination strategy. Single crystal X-ray structural analysis shows that the cluster has a distorted centered icosahedral Au@Au6Ag6 core of D 3 symmetry, in contrast to the I h Au@Au12 kernel in the well-known [Au25(SR)18]- (R = CH2CH2Ph). An interesting feature is the coexistence of [Au2(SPhOMe)3] dimeric staples and [P-Au-SPhOMe] semi-staples in the title cluster, due to the incorporation of PPh3. The observation of only one double-charged peak in ESI-TOF-MS confirms the ordered doping of silver atoms. Au19Ag6 is a 6e system showing a distinct absorption spectrum from [Au25(SR)18]-, that is, the HOMO-LUMO transition of Au19Ag6 is optically forbidden due to the P character of the superatomic frontier orbitals.

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.

Atomic structure of a seed-sized gold nanoprism

The growth of nanoparticles along one or two directions leads to anisotropic nanoparticles, but the nucleation (i.e., the formation of small seeds of specific shape) has long been elusive. Here, we show the total structure of a seed-sized Au₅₆ nanoprism, in which the side Au{100} facets are surrounded by bridging thiolates, whereas the top/bottom {111} facets are capped by phosphine ligands at the corners and Br⁻ at the center. The bromide has been proved to be the key to effectively stabilize the Au{111} to fulfill a complete face-centered-cubic core. In femtosecond electron dynamics analysis, the non-evolution of transient absorption spectra of Au₅₆ is similar to that of larger-sized gold nanoclusters (n > 100), which is ascribed to the completeness of the prismatic Au₅₆ core and an effective electron relaxation pathway created by the stronger Au-Au bonds inside. This work provides some insights for the understanding of plasmonic nanoprism formation.

The formation pathway of shape-anisotropic nanoparticles is difficult to characterize and not well understood. The authors synthesize a prismatic-shaped Au₅₆ nanocluster as possible seed of a prismatic nanoparticle and characterize the structure and ligand bonding motifs, providing insight into the formation and surface protection mechanisms.

A 59-Electron Non-Magic-Number Gold Nanocluster Au99(C≡CR)40 Showing Unexpectedly High Stability

An atomically resolved gold nanocluster Au₉₉(C≡CC₆H₃-2,4-F₂)₄₀ (Au₉₉) with an unusual 59 valence electrons has been synthesized. Single-crystal X-ray diffraction reveals that its Au₇₉ kernel is a Au₄₉ Marks decahedron capped by two Au₁₅ units. The surface structure of Au₉₉ consists of 20 linear Au(C≡CR)₂ staples. Intercluster interactions are observed between these D₅ symmetric clusters. The existence of an unpaired electron is verified by magnetic measurement. Interestingly, this open-shell gold cluster Au₉₉ stays intact in toluene solution at 80 °C for more than a week, and it has good charging-discharging capability under electrochemical conditions. The compact ligand shell protection around the symmetric core accounts for the high stability. This work suggests that geometric factors may play a crucial role in determining the stability of a metal nanocluster, even though the cluster has an open-shell electronic structure.

Superatomic Orbital Splitting in Coinage Metal Nanoclusters

The superatomic orbital splitting (SOS) method is developed to understand the electronic structures of coinage metal nanoclusters, in which delocalized electron counts are not magic numbers. Because the symmetry of a metal core can significantly affect the electronic structure of a nanocluster, this method takes the shape of the core into account in determining the order of group orbital levels. By taking nanoclusters as superatoms, a highly positively charged core is established by removing the ligands and staples. The superatomic orbitals split into group orbitals at different energy levels because of the nonspherical shape of the cluster core. Therefore, the electron configuration of the nonmagic-number nanocluster can be qualitatively analyzed without quantum chemical calculations, which is very important for understanding the stability of the cluster.

Origin of the structural stability of cage-like Au144 clusters

Cage-like metal nanoclusters are rarely found due to the densely packed property of metals. Recently, single crystallography has unraveled for the first time that multi-shell golden cages are formed in large-size thiolate (SR) and alkynl (CCR) protected neutral Au₁₄₄ nanoclusters, denoted as Au₁₄₄(SR)₆₀ and Au₁₄₄(CCR)₆₀. In this study, the origin of the structural stability of golden cage Au₁₄₄ clusters is studied based on the density functional theory (DFT) energy calculation and energy decomposition analysis (EDA). The formation of hollow cages rather than centre-filled icosahedrons in the Au₁₄₄ clusters is attributed to the significant Pauli repulsion between the central gold atom and the surrounding metal shell, which leads to the decrease of the averaged formation energy of the clusters. The present study also shows that the Au₁₄₄ cluster is unique in size. The smaller size clusters Au₁₃₃ and Au₁₃₀ and the larger size cluster Au₂₇₉ both preferred the centre-filled golden icosahedrons, decahedrons or octahedrons.

Programmable Metal Nanoclusters with Atomic Precision

With the recent establishment of atomically precise nanochemistry, capabilities toward programmable control over the nanoparticle size and structure are being developed. Advances in the synthesis of atomically precise nanoclusters (NCs, 1-3 nm) have been made in recent years, and more importantly, their total structures (core plus ligands) have been mapped out by X-ray crystallography. These ultrasmall Au nanoparticles exhibit strong quantum-confinement effect, manifested in their optical absorption properties. With the advantage of atomic precision, gold-thiolate nanoclusters (Au_n (SR)_m ) are revealed to contain an inner kernel, Au-S interface (motifs), and surface ligand (-R) shell. Programming the atomic packing into various crystallographic structures of the metal kernel can be achieved, which plays a significant role in determining the optical properties and the energy gap (E_g ) of NCs. When the size increases, a general trend is observed for NCs with fcc or decahedral kernels, whereas those NCs with icosahedral kernels deviate from the general trend by showing comparably smaller E_g . Comparisons are also made to further demonstrate the more decisive role of the kernel structure over surface motifs based on isomeric Au NCs and NC series with evolving kernel or motif structures. Finally, future perspectives are discussed.

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.

Molecular Gold Nanocluster Au156 Showing Metallic Electron Dynamics

The boundary between molecular and metallic gold nanoclusters is of special interest. The difficulty in obtaining atomically precise nanoclusters larger than 2 nm limits the determination of such a boundary. The synthesis and total structural determination of the largest all-alkynyl-protected gold nanocluster (Ph₄P)₆[Au₁₅₆(C≡CR)₆₀] (R = 4-CF₃C₆H₄-) (Au₁₅₆) are reported. It presents an ideal platform for studying the relationship between the structure and the metallic nature. Au₁₅₆ has a rod shape with the length and width of the kernel being 2.38 and 2.04 nm, respectively. The cluster contains a concentric Au₁₂₆ core structure (Au₄₆@Au₅₀@Au₃₀) protected by 30 linear RC≡C-Au-C≡CR staple motifs. It is interesting that Au₁₅₆ displays multiple excitonic peaks in the steady-state absorption spectrum (molecular) and pump-power-dependent excited-state dynamics as revealed in the transient absorption spectrum (metallic), which indicates that Au₁₅₆ is a critical crossover cluster for the transition from molecular to metallic state. Au₁₅₆ is the smallest-sized gold nanocluster showing metal-like electron dynamics, and it is recognized that the cluster shape is one of the important factors determining the molecular or metallic nature of a gold nanocluster.

Raman Spectroscopic Fingerprints of Atomically Precise Ligand Protected Noble Metal Clusters: Au38 (PET)24 and Au38-x Agx (PET)24

Distinct Raman spectroscopic signatures of the metal core of atomically precise, ligand-protected noble metal nanoclusters are reported using Au₃₈ (PET)₂₄ and Au_38-x Ag_x (PET)₂₄ (PET = 2-phenylethanethiolate, -SC₂ H₄ C₆ H₅ ) as model systems. The fingerprint Raman features (occurring <200 cm^-1 ) of these clusters arise due to the vibrations involving metal atoms of their Au₂₃ or Au_23-x Ag_x cores. A distinct core breathing vibrational mode of the Au₂₃ core has been observed at 90 cm^-1 . Whereas the breathing mode shifts to higher frequencies with increasing Ag content of the cluster, the vibrational signatures due to the outer metal-ligand staple motifs (between 200 and 500 cm^-1 ) do not shift significantly. DFT calculations furthermore reveal weak Raman bands at higher frequencies compared to the breathing mode, which are associated mostly with the rattling of two central gold atoms of the bi-icosahedral Au₂₃ core. These vibrations are also observed in the experimental spectrum. The study indicates that low-frequency Raman spectra are a characteristic fingerprint of atomically precise clusters, just as electronic absorption spectroscopy, in contrast to the spectrum associated with the ligand shell, which is observed at higher frequencies.

A Nanocluster [Ag307Cl62(SPhtBu)110]: Chloride Intercalation, Specific Electronic State, and Superstability

The controlling synthesis of novel nanoclusters of noble metals (Au, Ag) and the determination of their atomically precise structures provide opportunities for investigating their specific properties and applications. Here we report a novel silver nanocluster [Ag₃₀₇Cl₆₂(SPh^tBu)₁₁₀] (Ag₃₀₇) whose structure is determined by X-ray single crystal diffraction. The structure analysis shows that nanocluster Ag₃₀₇ contains a Ag₁₆₇ core, a surface shell of [Ag₁₄₀Cl₂S₁₁₀], and a Cl₆₀ intermediate layer located between Ag₁₆₇ and [Ag₁₄₀Cl₂S₁₁₀]. It is a first example that such many chlorides are intercalated into a Ag nanocluster. Chlorides are released in situ from solvent CHCl₃. Nanocluster Ag₃₀₇ exhibits superstability. Differential pulse voltammetry experiment reveals that Ag₃₀₇ has continuous charging/discharging behavior with a capacitance value of 1.39 aF, while the Ag₃₀₇ has a surface plasmonic feature. These characteristics show that Ag₃₀₇ is of metallic behavior. However, its electron paramagnetic resonance (EPR) spectra display a spin magnetic behavior which could be originated from the unpassivated dangling bonds of surface atoms. The direct capture of EPR signals can be attributed to the Cl^- intercalating layer which partly suppresses the electronic interactions between core and surface atoms, resulting in the relatively independent electronic states for core and surface atoms.

Diarsine- vs diphosphine-protected Au13 clusters: Effect of subtle geometric differences on optical property and electronic structure

In the design of ligand-protected metal clusters, the choice of protecting ligands is a critical factor because they can profoundly affect the nuclearity, geometry, and electronic structures to afford a diverse range of cluster compounds. Here, we report the synthesis of two novel diarsine-protected Au₁₃ clusters ([Au₁₃L₅Cl₂]³⁺, L = diarsine) and compare these clusters with diphosphine analogs in terms of the core geometry and optical properties. In the crystal structure, the cluster bearing C3-bridged diarsines {[Au₁₃(dpap)₅Cl₂]³⁺, 3} had an apparently identical icosahedral Au₁₃ core to [Au₁₃(dppe)₅Cl₂]³⁺ (1) with C2-bridged diphosphines, but slight structural differences associated with the bridging unit of the ligands were found. Despite similar icosahedral Au₁₃ cores 1 and 3, their absorption and photoluminescence profiles were evidently different. Theoretical calculations revealed that the subtle deformation of the Au₁₃ icosahedron, rather than the coordinating atoms (As or P), notably influences the electronic structure to cause the difference in the absorption profiles.

Ligand Design in Ligand-Protected Gold Nanoclusters

The design of surface ligands is crucial for ligand-protected gold nanoclusters (Au NCs). Besides providing good protection for Au NCs, the surface ligands also play the following two important roles: i) as the outermost layer of Au NCs, the ligands will directly interact with the exterior environment (e.g., solvents, molecules and cells) influencing Au NCs in various applications; and ii) the interfacial chemistry between ligands and gold atoms can determine the structures, as well as the physical and chemical properties of Au NCs. A delicate ligand design in Au NCs (or other metal NCs) needs to consider the covalent bonds between ligands and gold atoms (e.g., gold-sulfur (Au-S) and gold-phosphorus (Au-P) bond), the physics forces between ligands (e.g., hydrophobic and van der Waals forces), and the ionic forces between the functional groups of ligands (e.g., carboxylic (COOH) and amine group (NH₂ )); which form the underlying chemistry and discussion focus of this review article. Here, detailed discussions on the effects of surface ligands (e.g., thiolate, phosphine, and alkynyl ligands; or hydrophobic and hydrophilic ligands) on the synthesis, structures, and properties of Au NCs; highlighting the design principles in the surface engineering of Au NCs for diverse emerging applications, are provided.

An Au2S network model for exploring the structural origin, evolution, and two-electron (2e-) reduction growth mechanism of Aun(SR)m clusters

An Au₂S network model was proposed to study the structural origin, evolution, and formation mechanism of the Au_n(SR)_m clusters containing quasi-face-centered-cubic (fcc) cores. The Au-S framework structures of 20 quasi-fcc gold clusters had been determined from the Au₂S network. Based on the Au₂S network, some new quasi-fcc clusters, such as 8e^- clusters Au₂₄(SR)₁₆, Au₂₆(SR)₁₈, Au₂₆(SR)₁₉ ^-, Au₂₉(SR)₂₁, Au₃₀(SR)₂₂, and Au₃₂(SR)₂₄, and a class of Au_24+8n(SR)_20+4n (n = 1, 2, 3, …) clusters were predicted. Furthermore, by studying the evolution of Au-S frameworks, it was possible to construct molecular-like reaction equations to account for the formation mechanism of quasi-fcc gold clusters, which indicated that the formation of quasi-fcc gold clusters can be understood from the stepwise 2e^--reduction cluster growth pathways. The present studies showed that the Au₂S network model provided a "parental" Au-S network for exploring the structural evolution of the quasi-fcc Au_n(SR)_m clusters. Moreover, it was possible to study the formation pathways of the Au_n(SR)_m clusters by studying the evolution of their Au-S frameworks.

The ligand effect on the interface structures and electrocatalytic applications of atomically precise metal nanoclusters

Metal nanoclusters, also known as ultra-small metal nanoparticles, occupy the gap between discrete atoms and plasmonic nanomaterials, and are an emerging class of atomically precise nanomaterials. Metal nanoclusters protected by different types of ligands, such as thiolates, alkynyls, hydrides, and N-heterocyclic carbenes, have been synthesized in recent years. Moreover, recent experiment and theoretical studies also indicated that the metal nanoclusters show great promise in many electrocatalytic reactions, such as hydrogen evolution, oxygen reduction, and CO₂reduction. The atomically precise nature of their structures enables the elucidation of structure-property relationships and the reaction mechanisms, which is essential if nanoclusters with enhanced performances are to be rationally designed. Particularly, the ligands play an important role in affecting the interface bonding, stability and electrocatalytic activity/selectivity. In this review, we mainly focus on the ligand effect on the interface structure of metal nanoclusters and then discuss the recent advances in electrocatalytic applications. Furthermore, we point out our perspectives on future efforts in this field.

Metal-Ligand Interface and Internal Structure of Ultrasmall Silver Nanoparticles (2 nm)

Ultrasmall silver nanoparticles were prepared by reduction with NaBH₄ and surface-terminated with glutathione (GSH). The particles had a solid core diameter of 2 nm as shown by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). NMR-DOSY gave a hydrodynamic diameter of 2 to 2.8 nm. X-ray photoelectron spectroscopy (XPS) showed that silver is bound to the thiol group of the central cysteine in glutathione under partial oxidation to silver(+I). In turn, the thiol group is deprotonated to thiolate. X-ray powder diffraction (XRD) together with Rietveld refinement confirmed a twinned (polycrystalline) fcc structure of ultrasmall silver nanoparticles with a lattice compression of about 0.9% compared to bulk silver metal. By NMR spectroscopy, the interaction between the glutathione ligand and the silver surface was analyzed, also with ¹³C-labeled glutathione. The adsorbed glutathione is fully intact and binds to the silver surface via cysteine. In situ ¹H NMR spectroscopy up to 85 °C in dispersion showed that the glutathione ligand did not detach from the surface of the silver nanoparticle, i.e. the silver-sulfur bond is remarkably strong. The ultrasmall nanoparticles had a higher cytotoxicity than bigger particles in in vitro cell culture with HeLa cells with a cytotoxic concentration of about 1 μg mL^-1 after 24 h incubation. The overall stoichiometry of the nanoparticles was about Ag_∼250GSH_∼155.

Design of a fluorescent and clickable Ag38(SRN3)24 nanocluster platform: synthesis, modeling and self-assembling

Fluorescent atomically precise Ag₃₈(11-azido-2-ol-undecane-thiolate)₂₄ nanoclusters are easily prepared using sodium ascorbate as a "green" reducer and are extensively characterized by way of elemental analyses, ATR-FTIR, XRD, SAXS, UV-vis, fluorescence spectroscopies, and theoretical modeling. The fluorescence and the atomically determined stoichiometry and structure, the facile and environmentally green synthesis, together with the novel presence of terminal azido groups in the ligands which opens the way to "click"-binding a wide set of molecular species, make Ag₃₈(11-azido-2-ol-undecane-thiolate)₂₄ nanoclusters uniquely appealing systems for biosensing, recognition and functionalization in biomedicine applications and in catalysis.

Fine-Tuning Synthesis of Fluorescent Silver Thiolate Nanoclusters

Noble metal thiolate nanoclusters are a new class of nanomaterials with molecular-like properties such as high dispersibility and fluorescence in the visible and infrared spectral region, properties highly requested in biomedicine for imaging, sensing and drug delivery applications. We report on three new silver phenylethane thiolate nanoclusters, differing for slight modifications of the preparation, i.e., the reaction solvent and the thiolate quantity, producing changes in the nanocluster composition as well as in the fluorescence behavior. All samples, excited in the range 250-500 nm, emit around 400 and 700 nm differing in the emission maxima and behavior. The silver thiolate nanoclusters have been characterized by way of C, H, S elemental analyses and Thermal Gravimetric Analysis (TGA) to determine the nanocluster composition, Scanning Transmission Electron Microscopy (STEM) to investigate the nanocluster morphology and UV-Vis and fluorescence spectroscopy to study their optical properties.

Ligand exchange reactions on thiolate-protected gold nanoclusters

As a versatile post-synthesis modification method, ligand exchange reaction exhibits great potential to extend the space of accessible nanoclusters. In this review, we summarized this process for thiolate-protected gold nanoclusters. In order to better understand this reaction we will first provide the necessary background on the synthesis and structure of various gold clusters, such as Au25(SR)18, Au38(SR)24, and Au102(SR)44. The previous investigations illustrated that ligand exchange is enabled by the chemical properties and flexible gold-sulfur interface of nanoclusters. It is generally believed that ligand exchange follows a SN2-like mechanism, which is supported both by experiments and calculations. More interesting, several studies show that ligand exchange takes place at preferred sites, i.e. thiolate groups -SR, on the ligand shell of nanoclusters. With the help of ligand exchange reactions many functionalities could be imparted to gold nanoclusters including the introduced of chirality to achiral nanoclusters, size transformation and phase transfer of nanoclusters, and the addition of fluorescence or biological labels. Ligand exchange was also used to amplify the enantiomeric excess of an intrinsically chiral cluster. Ligand exchange reaction accelerates the prosperity of the nanocluster field, and also extends the diversity of precise nanoclusters.

[Ag9(1,2-BDT)6]3-: How Square-Pyramidal Building Blocks Self-Assemble into the Smallest Silver Nanocluster

The emerging promise of few-atom metal catalysts has driven the need for developing metal nanoclusters (NCs) with ultrasmall core size. However, the preparation of metal NCs with single-digit metallic atoms and atomic precision is a major challenge for materials chemists, particularly for Ag, where the structure of such NCs remains unknown. In this study, we developed a shape-controlled synthesis strategy based on an isomeric dithiol ligand to yield the smallest crystallized Ag NC to date: [Ag9(1,2-BDT)6]3- (1,2-BDT = 1,2-benzenedithiolate). The NC's crystal structure reveals the self-assembly of two Ag square pyramids through preferential pyramidal vertex sharing of a single metallic Ag atom, while all other Ag atoms are incorporated in a motif with thiolate ligands, resulting in an elongated body-centered Ag9 skeleton. Steric hindrance and arrangement of the dithiolated ligands on the surface favor the formation of an anisotropic shape. Time-dependent density functional theory based calculations reproduce the experimental optical absorption features and identify the molecular orbitals responsible for the electronic transitions. Our findings will open new avenues for the design of novel single-digit metal NCs with directional self-assembled building blocks.

Insights and Perspectives Regarding Nanostructured Fluorescent Materials toward Tackling COVID-19 and Future Pandemics

The COVID-19 outbreak has exposed the world's preparation to fight against unknown/unexplored infectious and life-threatening pathogens. The unavailability of vaccines, slow or sometimes unreliable real-time virus/bacteria detection techniques, insufficient personal protective equipment (PPE), and a shortage of ventilators and many other transportation equipments have further raised serious concerns. Material research has been playing a pivotal role in developing antimicrobial agents for water treatment and photodynamic therapy, fast and ultrasensitive biosensors for virus/biomarkers detection, as well as for relevant biomedical and environmental applications. It has been noticed that these research efforts nowadays primarily focus on the nanomaterials-based platforms owing to their simplicity, reliability, and feasibility. In particular, nanostructured fluorescent materials have shown key potential due to their fascinating optical and unique properties at the nanoscale to combat against a COVID-19 kind of pandemic. Keeping these points in mind, this review attempts to give a perspective on the four key fluorescent materials of different families, including carbon dots, metal nanoclusters, aggregation-induced-emission luminogens, and MXenes, which possess great potential for the development of ultrasensitive biosensors and infective antimicrobial agents to fight against various infections/diseases. Particular emphasis has been given to the biomedical and environmental applications that are linked directly or indirectly to the efforts in combating COVID-19 pandemics. This review also aims to raise the awareness of researchers and scientists across the world to utilize such powerful materials in tackling similar pandemics in future.

Chiroptical activity of Au13 clusters: experimental and theoretical understanding of the origin of helical charge movements

Ligand-protected gold clusters with an asymmetric nature have emerged as a novel class of chiral compounds, but the origins of their chiroptical activities associated with helical charge movements in electronic transitions remain unexplored. Herein, we perform experimental and theoretical studies on the structures and chiroptical properties of Au13 clusters protected by mono- and di-phosphine ligands. Based on the experimental reevaluation of diphosphine-ligated Au13 clusters, we show that these surface ligands slightly twist the Au13 cores from a true icosahedron to generate intrinsic chirality in the gold frameworks. Theoretical investigation of a monophosphine-ligated cluster model reproduced the experimentally observed circular dichroism (CD) spectrum, indicating that such a torsional twist of the Au13 core, rather than the surrounding chiral environment by helically arranged diphosphine ligands, contributes to the appearance of the chiroptical response. We also show that the calculated CD signals are dependent on the degree of asymmetry (torsion angle between the two equatorial Au5 pentagons), and provide a visual understanding of the origin of helical charge movements with transition-moment and transition-density analyses. This work provides novel insights into the chiroptical activities of ligand-protected metal clusters with intrinsically chiral cores.

Enriching Structural Diversity of Alkynyl-Protected Gold Nanoclusters with Chlorides

The synthesis and isolation of alkynyl/chloride-protected gold nanoclusters is described. Silica gel column chromatography is effective in isolating gold nanoclusters from the as-synthesized cluster mixture to give the clusters Na[Au₂₅ L₁₈ ] (Au₂₅ ), [HNEt₃ ]₃ [Au₆₇ L₃₂ Cl₄ ] (Au₆₇ ), [HNEt₃ ]₄ [Au₁₀₆ L₄₀ Cl₁₂ ] (Au₁₀₆ ), L=3,5-bis(trifluoromethyl)-phenylacetylide. Au₆₇ and Au₁₀₆ are new clusters; the structures were determined by X-ray single-crystal diffraction. Au₆₇ contains a distorted Au₁₈ Marks decahedron shelled by an irregular Au₃₂ and further protected with two V-shaped Au₂ L₃ , 13 linear AuL₂ staples and 4 chlorides. Au₆₇ is the first structurally determined 34e superatomic gold nanocluster. Au₁₀₆ is composed of 106 Au atoms co-protected by alkynyls and chlorides. It has a Au₇₉ kernel, like in Au₁₀₂ (p-MBA)₄₄ . The surface structure of Au₁₀₆ includes 20 linear Au-alkynyl staples, 5 Cl-Au-Cl and 2 Cl-Au motifs. These three gold nanoclusters show size-dependent electrochemical properties.

Metalloid gold clusters - past, current and future aspects

Gold chemistry and the synthesis of colloidal gold have always caught the attention of scientists. While Faraday was investigating the physical properties of colloidal gold in 1857 without probably knowing anything about the exact structure of the molecules, 150 years later the working group of Kornberg synthesized the first structurally characterized multi-shell metalloid gold cluster with more than 100 Au atoms, Au102(SR)44. After this ground-breaking result, many smaller and bigger metalloid gold clusters have been discovered to gain a better understanding of the formation process and the physical properties. In this review, first of all, a general overview of past investigations is given, leading to metalloid gold clusters with staple motifs in the ligand shell, highlighting structural differences in the cores of these clusters. Afterwards, the influence of the synthetic procedure on the outcome of the reactions is discussed, focusing on recent results from our group. Thereby, newly found structural motifs are taken into account and compared to the existing ones. Finally, a short outlook on possible subsequent reactions of these metalloid gold clusters is given.

Controlling the Surface Functionalization of Ultrasmall Gold Nanoparticles by Sequence-Defined Macromolecules

Ultrasmall gold nanoparticles (diameter about 2 nm) were surface-functionalized with cysteine-carrying precision macromolecules. These consisted of sequence-defined oligo(amidoamine)s (OAAs) with either two or six cysteine molecules for binding to the gold surface and either with or without a PEG chain (3400 Da). They were characterized by 1 H NMR spectroscopy, 1 H NMR diffusion-ordered spectroscopy (DOSY), small-angle X-ray scattering (SAXS), and high-resolution transmission electron microscopy. The number of precision macromolecules per nanoparticle was determined after fluorescent labeling by UV spectroscopy and also by quantitative 1 H NMR spectroscopy. Each nanoparticle carried between 40 and 100 OAA ligands, depending on the number of cysteine units per OAA. The footprint of each ligand was about 0.074 nm2 per cysteine molecule. OAAs are well suited to stabilize ultrasmall gold nanoparticles by selective surface conjugation and can be used to selectively cover their surface. The presence of the PEG chain considerably increased the hydrodynamic diameter of both dissolved macromolecules and macromolecule-conjugated gold nanoparticles.

A construction guide for high-nuclearity (≥50 metal atoms) coinage metal clusters at the nanoscale: bridging molecular precise constructs with the bulk material phase

Synthesis remains a major strength in chemistry and materials science and relies on the formation of new molecules and diverse forms of matter. The construction and identification of large molecules poses specific challenges and has historically lain in the realm of biological (organic)-type molecules with evolved synthesis methods to support such endeavours. But with the development of analytical tools such as X-ray crystallography, new synthesis methods toward large metal-based (inorganic) molecules and clusters have come to the fore, making it possible to accurately determine the precise distribution of hundreds of atoms in large clusters. In this review, we focus on different synthesis protocols used to form new metal clusters such as templating, alloying and size-focusing strategies. A specific focus is on group 11 metals (Cu, Ag, Au) as they currently predominate large metal cluster investigations and related Au and Ag bulk surface phenomena. This review focuses on metal clusters that have very high-nuclearity, i.e. with 50 or more metal centers within the isolated cluster. This size domain, it is believed, will become increasingly important for a variety of applications as these metal clusters are positioned at the interface between the molecular and bulk phases, whilst remaining a classic nanomaterial and retaining unique nano-sized properties.

Controlling ultrasmall gold nanoparticles with atomic precision

Gold nanoparticles are probably the nanoparticles that have been best studied for the longest time due to their stability, physicochemical properties and applications. Controlling gold nanoparticles with atomic precision is of significance for subsequent research on their structures, properties and applications, which is a dream that has been pursued for many years since ruby gold was first obtained by Faraday in 1857. Fortunately, this dream has recently been partially realized for some ultrasmall gold nanoparticles (nanoclusters). However, rationally designing and synthesizing gold nanoparticles with atomic precision are still distant goals, and this challenge might rely primarily on rich atomically precise gold nanoparticle libraries and the in-depth understanding of metal nanoparticle chemistry. Herein, we review general synthesis strategies and some facile synthesis methods, with an emphasis on the controlling parameters determined from well-documented results, which might have important implications for future nanoparticle synthesis with atomic precision and facilitate related research and applications.

Chirality and Surface Bonding Correlation in Atomically Precise Metal Nanoclusters

Chirality is ubiquitous in nature and occurs at all length scales. The development of applications for chiral nanostructures is rising rapidly. With the recent achievements of atomically precise nanochemistry, total structures of ligand-protected Au and other metal nanoclusters (NCs) are successfully obtained, and the origins of chirality are discovered to be associated with different parts of the cluster, including the surface ligands (e.g., swirl patterns), the organic-inorganic interface (e.g., helical stripes), and the kernel. Herein, a unified picture of metal-ligand surface bonding-induced chirality for the nanoclusters is proposed. The different bonding modes of M-X (where M = metal and X = the binding atom of ligand) lead to different surface structures on nanoclusters, which in turn give rise to various characteristic features of chirality. A comparison of Au-thiolate NCs with Au-phosphine ones further reveals the important roles of surface bonding. Compared to the Au-thiolate NCs, the Ag/Cu/Cd-thiolate systems exhibit different coordination modes between the metal and the thiolate. Other than thiolate and phosphine ligands, alkynyls are also briefly discussed. Several methods of obtaining chiroptically active nanoclusters are introduced, such as enantioseparation by high-performance liquid chromatography and enantioselective synthesis. Future perspectives on chiral NCs are also proposed.

Isomerization-induced enhancement of luminescence in Au28(SR)20 nanoclusters

Understanding the origin and structural basis of the photoluminescence (PL) phenomenon in thiolate-protected metal nanoclusters is of paramount importance for both fundamental science and practical applications. It remains a major challenge to correlate the PL properties with the atomic-level structure due to the complex interplay of the metal core (i.e. the inner kernel) and the exterior shell (i.e. surface Au(i)-thiolate staple motifs). Decoupling these two intertwined structural factors is critical in order to understand the PL origin. Herein, we utilize two Au₂₈(SR)₂₀ nanoclusters with different –R groups, which possess the same core but different shell structures and thus provide an ideal system for the PL study. We discover that the Au₂₈(CHT)₂₀ (CHT: cyclohexanethiolate) nanocluster exhibits a more than 15-fold higher PL quantum yield than the Au₂₈(TBBT)₂₀ nanocluster (TBBT: p-tert-butylbenzenethiolate). Such an enhancement is found to originate from the different structural arrangement of the staple motifs in the shell, which modifies the electron relaxation dynamics in the inner core to different extents for the two nanoclusters. The emergence of a long PL lifetime component in the more emissive Au₂₈(CHT)₂₀ nanocluster reveals that its PL is enhanced by suppressing the nonradiative pathway. The presence of long, interlocked staple motifs is further identified as a key structural parameter that favors the luminescence. Overall, this work offers structural insights into the PL origin in Au₂₈(SR)₂₀ nanoclusters and provides some guidelines for designing luminescent metal nanoclusters for sensing and optoelectronic applications.

Two Au₂₈(SR)₂₀ nanoclusters with an identical core but different shells exhibit a ∼15-fold difference in photoluminescence.

From Monolayer-Protected Gold Cluster to Monolayer-Protected Gold-Sulfide Cluster: Geometrical and Electronic Structure Evolutions of Au60S n (SR)36 (n = 0-12)

Thiolate-monolayer-protected gold clusters are usually formulated as AuNSR[Au(I)-SR] x , where AuN and SR[Au(I)-SR] x (x = 0, 1, 2, ...) are the inner gold core and outer protection motifs, respectively. In this work, we theoretically envision a new family of S-atom-doped thiolate-monolayer-protected gold clusters, namely, Au60S n (SR)36 (n = 0-12). A distinct feature of Au60S n (SR)36 nanoclusters (NCs) is that they show a gradual transition from the monolayer-protected metal NC to the SR[Au(I)-(SR)] x oligomer-protected gold-sulfide cluster with the increase of the number of doping S atoms. The possible formation mechanism of the S-atom-doped thiolate-protected gold cluster is investigated, and the size-dependent stability and electronic and optical absorption properties of Au60S n (SR)36 are explored using density functional theory (DFT) calculations. It is found that doping of S atom significantly tails the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap and optical absorption properties of thiolate-protected gold cluster, representing a promising way to fabricate new monolayer-protected gold nanoparticles.