Same Magic Number but Different Arrangement: Alkynyl‐Protected Au25 with D3 Symmetry

Two homoleptic alkynyl‐protected gold clusters with compositions of Na[Au₂₅(C≡CAr)₁₈] and (Ph₄P)[Au₂₅(C≡CAr)₁₈] (Na? 1 and Ph₄P? 1 , Ar=3,5‐bis(trifluoromethyl)phenyl) were synthesized via a direct reduction method. 1 is a magic cluster analogous to [Au₂₅(SR)₁₈]^? in terms of electron counts and metal‐to‐ligand ratio. Single‐crystal structure analysis reveals that 1 has an identical Au₁₃ kernel to [Au₂₅(SR)₁₈]^?, but adopts a distinctly different arrangement of the six peripheral dimer staple motifs. The steric hindrance of alkynyl ligands is responsible for the D₃ arrangement of Au₂₅. The introduction of alkynyl also significantly changes the optical absorption features of the nanocluster as supported by DFT calculations. This magic cluster confirms that there is a similar but quite different parallel alkynyl‐protected metal cluster universe in comparison to the thiolated one.     

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

We report the X‐ray structure of a gold nanocluster with 30 gold atoms protected by 18 1‐adamantanethiolate ligands (formulated as Au₃₀(S‐Adm)₁₈). This nanocluster exhibits a threefold rotationally symmetrical, hexagonal‐close‐packed (HCP) Au₁₈ kernel protected by six dimeric Au₂(SR)₃ staple motifs. This new structure is distinctly different from the previously reported Au₃₀S(S‐^tBu)₁₈ nanocluster protected by 18 tert‐butylthiolate ligands and one sulfido ligand with a face‐centered cubic (FCC) Au₂₂ kernel. The Au₃₀(S‐Adm)₁₈ nanocluster has an anomalous solubility (it is only soluble in benzene but not in other common solvents). This work demonstrates a ligand‐based strategy for controlling nanocluster structure and also provides a method for the discovery of possibly overlooked clusters because of their anomalous solubility.     

Structure Determination of Alkynyl‐Protected Gold Nanocluster Au22(tBuC≡C)18 and Its Thermochromic Luminescence

An alkynyl‐protected gold nanocluster, Au₂₂(^tBuC≡C)₁₈ ( 1 ), has been synthesized and its structure has been determined by single‐crystal X‐ray diffraction. The molecular structure consists of a Au₁₃ cuboctahedron kernel and three [Au₃(^tBuC≡C)₄] trimeric staples. The cluster 1 has strong luminescence in the solid state with a 15 % quantum yield, and it displays interesting thermochromic luminescence as revealed by temperature‐dependent emission spectra. The enhanced room‐temperature emission is characterized as thermally activated delayed fluorescence.     

An Atomically Precise Au10Ag2 Nanocluster with Red–Near‐IR Dual Emission

A red–near‐IR dual‐emissive nanocluster with the composition [Au₁₀Ag₂(2‐py?C≡C)₃(dppy)₆](BF₄)₅ ( 1 ; 2‐py?C≡C is 2‐pyridylethynyl, dppy=2‐pyridyldiphenylphosphine) has been synthesized. Single‐crystal X‐ray structural analysis reveals that 1 has a trigonal bipyramidal Au₁₀Ag₂ core that contains a planar Au₄(2‐py?C≡C)₃ unit sandwiched by two Au₃Ag(dppy)₃ motifs. Cluster 1 shows intense red–NIR dual emission in solution. The visible emission originates from metal‐to‐ligand charge transfer (MLCT) from silver atoms to phosphine ligands in the Au₃Ag(dppy)₃ motifs, and the intense NIR emission is associated with the participation of 2‐pyridylethynyl in the frontier orbitals of the cluster, which is confirmed by a time‐dependent density functional theory (TD‐DFT) calculation.     

Alkynyl‐Protected Au23 Nanocluster: A 12‐Electron System

A 23‐gold‐atom nanocluster was prepared by NaBH₄‐mediated reduction of a solution of PhC?CAu and Ph₃PAuSbF₆ in CH₂Cl₂. The cluster composition was determined to be [Au₂₃(PhC?C)₉(Ph₃P)₆]²⁺ and single‐crystal X‐ray diffraction revealed that the cluster has an unprecedented Au₁₇ kernel protected by three PhC₂‐Au‐C₂(Ph)‐Au‐C₂Ph motifs and six Ph₃P groups. The Au₁₇ core can be viewed as the fusion of two Au₁₀ units sharing a Au₃ triangle. Electronic structure analysis from DFT calculations suggests that the stability of this unusual 12‐electron cluster is a result of the splitting of the superatomic 1D orbitals under D_3h symmetry of the Au₁₇ kernel. The discovery and determination of the structure of the Au₂₃ cluster demonstrates the versatility of the alkynyl ligand in leading to the formation of new cluster compounds.     

A Near‐Infrared‐Emissive Alkynyl‐Protected Au24 Nanocluster

An alkynyl‐protected gold nanocluster [Au₂₄(C?CPh)₁₄(PPh₃)₄](SbF₆)₂ has been prepared by a direct reduction method. Single‐crystal X‐ray diffraction reveals that the molecular structure contains a Au₂₂ core that is made of two Au₁₃‐centered cuboctahedra that share a square face. Two staple‐like PhC?C? Au? C?CPh motifs are located around the center of the rod‐like Au₂₂ core. This Au₂₄ nanocluster is highly emissive in the near‐infrared region with λ_max=925 nm and the nature of the HOMO–LUMO transition is investigated by time‐dependent DFT calculations.     

A Ligand‐Protected Golden Fullerene: The Dipyridylamido Au328+ Nanocluster

A golden fullerene Au₃₂ cluster has been synthesized with amido and phosphine ligands as the protecting agents. Single‐crystal X‐ray structural analysis revealed that this gold nanocluster, [Au₃₂(Ph₃P)₈(dpa)₆] (SbF₆)₂ (Hdpa=2,2′‐dipyridylamine), has a stable pseudo‐I_h Au₃₂⁸⁺ core with S₆ symmetry, which features an Au₁₂@Au₂₀ Keplerate cage co‐protected by Ph₃P and dpa ligands. Quantum‐chemical studies were conducted to elucidate the origin of the special stability of this cluster, and suggest that it is electronically stabilized through metal–ligand interactions.     

Formation of an Alkynyl‐Protected Ag112 Silver Nanocluster as Promoted by Chloride Released In Situ from CH2Cl2

By directly reducing alkynyl–silver precursors, we successfully obtained a large alkynyl‐protected silver nanocluster, (C₇H₁₇ClN)₃[Ag₁₁₂Cl₆(C≡CAr)₅₁], which is hitherto the largest structurally characterized silver nanocluster in the alkynyl family. The cluster exhibits four concentric core–shell structures (Ag₁₃@Ag₄₂@Ag₄₈@Ag₉), and four types of alkynyl–silver binding modes are observed. Chloride was found to be critical for the stabilization and formation of the silver nanocluster. The release of chloride ions in situ from CH₂Cl₂ solvent has been confirmed by mass spectrometry. This study suggests that the combination of alkynyl and halide ligands will pave a new way for the synthesis of large silver nanoclusters.     

Homoleptic Alkynyl‐Protected Gold Nanoclusters: Au44(PhC≡C)28 and Au36(PhC≡C)24

For the first time total structure determination of homoleptic alkynyl‐protected gold nanoclusters is reported. The nanoclusters are synthesized by direct reduction of PhC≡CAu, to give Au₄₄(PhC≡C)₂₈ and Au₃₆(PhC≡C)₂₄. The Au₄₄ and Au₃₆ nanoclusters have fcc‐type Au₃₆ and Au₂₈ kernels, respectively, as well as surrounding PhC≡C‐Au‐C₂(Ph)Au‐C≡CPh dimeric “staples” and simple PhC≡C bridges. The structures of Au₄₄(PhC≡C)₂₈ and Au₃₆(PhC≡C)₂₄ are similar to Au₄₄(SR)₂₈ and Au₃₆(SR)₂₄, but the UV/Vis spectra are different. The protecting ligands influence the electronic structures of nanoclusters significantly. The synthesis of these two alkynyl‐protected gold nanoclusters indicates that a series of gold nanoclusters in the general formula Au_x (RC≡C)_y as counterparts to Au_x (SR)_y can be expected.     

An All‐Alkynyl Protected 74‐Nuclei Silver(I)–Copper(I)‐Oxo Nanocluster: Oxo‐Induced Hierarchical Bimetal Aggregation and Anisotropic Surface Ligand Orientation

The hardness of oxo ions (O^2?) means that coinage‐metal (Cu, Ag, Au) clusters supported by oxo ions (O^2?) are rare. Herein, a novel μ₄‐oxo supported all‐alkynyl‐protected silver(I)–copper(I) nanocluster [Ag_74?xCu_xO₁₂(PhC≡C)₅₀] ( NC‐1 , avg. x=37.9) is characterized. NC‐1 is the highest nuclearity silver–copper heterometallic cluster and contains an unprecedented twelve interstitial μ₄‐oxo ions. The oxo ions originate from the reduction of nitrate ions by NaBH₄. The oxo ions induce the hierarchical aggregation of Cu^I and Ag^I ions in the cluster, forming the unique regioselective distribution of two different metal ions. The anisotropic ligand coverage on the surface is caused by the jigsaw‐puzzle‐like cluster packing incorporating rare intermolecular C?H???metal agostic interactions and solvent molecules. This work not only reveals a new category of high‐nuclearity coinage‐metal clusters but shows the special clustering effect of oxo ions in the assembly of coinage‐metal clusters.     

Structure Determination of Alkynyl-Protected Gold Nanocluster Au22(tBuC≡C)18 and Its Thermochromic Luminescence

An alkynyl-protected gold nanocluster, Au₂₂(^tBuC≡C)₁₈ ( 1 ), has been synthesized and its structure has been determined by single-crystal X-ray diffraction. The molecular structure consists of a Au₁₃ cuboctahedron kernel and three [Au₃(^tBuC≡C)₄] trimeric staples. The cluster 1 has strong luminescence in the solid state with a 15 % quantum yield, and it displays interesting thermochromic luminescence as revealed by temperature-dependent emission spectra. The enhanced room-temperature emission is characterized as thermally activated delayed fluorescence.     

Au57Ag53(C≡CPh)40Br12: A Large Nanocluster with C1 Symmetry

The controlled synthesis and structure determination of a bimetallic nanocluster Au₅₇Ag₅₃(C≡CPh)₄₀Br₁₂ (Au₅₇Ag₅₃) is presented. The metal core has a four‐shell Au₂M₃@Au₃₄@Ag₅₁ @Au₂₀ (M=1/3 Au+2/3 Ag) architecture. In contrast to the previously reported large nanoclusters that have highly symmetric kernel structures, the metal atoms in Au₅₇Ag₅₃ are arranged in an irregular manner with C₁ symmetry. This cluster exhibits excellent thermal stability and is robust under oxidative or basic conditions. The silver precursors play a key role in dictating the structures of the nanoclusters, which suggests the importance of the counteranions used.     

Fcc versus Non‐fcc Structural Isomerism of Gold Nanoparticles with Kernel Atom Packing Dependent Photoluminescence

Structural isomerism allows the correlation between structures and properties to be investigated. Unfortunately, the structural isomers of metal nanoparticles are rare and genuine structural isomerism with distinctly different kernel atom packing (e.g., face‐centered cubic (fcc) vs. non‐fcc) has not been reported until now. Herein we introduce a novel ion‐induction method to synthesize a unique gold nanocluster with a twist mirror symmetry structure. The as‐synthesized nanocluster has the same composition but different kernel atom packing to an existing gold nanocluster Au₄₂(TBBT)₂₆ (TBBT=4‐tert‐butylbenzenethiolate). The fcc‐structured Au₄₂(TBBT)₂₆ nanocluster shows more enhanced photoluminescence than the non‐fcc‐structured Au₄₂(TBBT)₂₆ nanocluster, indicating that the fcc‐structure is more beneficial for emission than the non‐fcc structure. This idea was supported by comparison of the emission intensity of another three pairs of gold nanoclusters with similar compositions and sizes but with different kernel atom packings (fcc vs. non‐fcc).     

Highly Robust but Surface‐Active: An N‐Heterocyclic Carbene‐Stabilized Au25 Nanocluster

Surface organic ligands play a critical role in stabilizing atomically precise metal nanoclusters in solutions. However, it is still challenging to prepare highly robust ligated metal nanoclusters that are surface‐active for liquid‐phase catalysis without any pre‐treatment. Now, an N‐heterocyclic carbene‐stabilized Au₂₅ nanocluster with high thermal and air stabilities is presented as a homogenous catalyst for cycloisomerization of alkynyl amines to indoles. The nanocluster, characterized as [Au₂₅(ⁱPr₂‐bimy)₁₀Br₇]²⁺ (ⁱPr₂‐bimy=1,3‐diisopropylbenzimidazolin‐2‐ylidene) ( 1 ), was synthesized by direct reduction of AuSMe₂Cl and ⁱPr₂‐bimyAuBr with NaBH₄ in one pot. X‐ray crystallization analysis revealed that the cluster comprises two centered Au₁₃ icosahedra sharing a vertex. Cluster 1 is highly stable and can survive in solution at 80 °C for 12 h, which is superior to Au₂₅ nanoclusters passivated with phosphines or thiols. DFT computations reveal the origins of both electronic and thermal stability of 1 and point to the probable catalytic sites. This work provides new insights into the bonding capability of N‐heterocyclic carbene to Au in a cluster, and offers an opportunity to probe the catalytic mechanism at the atomic level.     

Balancing the Rate of Cluster Growth and Etching for Gram‐Scale Synthesis of Thiolate‐Protected Au25 Nanoclusters with Atomic Precision

We report a NaOH‐mediated NaBH₄ reduction method for the synthesis of mono‐, bi‐, and tri‐thiolate‐protected Au₂₅ nanoclusters (NCs) with precise control of both the Au core and thiolate ligand surface. The key strategy is to use NaOH to tune the formation kinetics of Au NCs, i.e., reduce the reduction ability of NaBH₄ and accelerate the etching ability of free thiolate ligands, leading to a well‐balanced reversible reaction for rapid formation of thermodynamically favorable Au₂₅ NCs. This protocol is facile, rapid (≤3 h), versatile (applicable for various thiolate ligands), and highly scalable (>1 g Au NCs). In addition, bi‐ and tri‐thiolate‐protected Au₂₅ NCs with adjustable ratios of hetero‐thiolate ligands were easily obtained. Such ligand precision in molecular ratios, spatial distribution and uniformity resulted in richly diverse surface landscapes on the Au NCs consisting of multiple functional groups such as carboxyl, amine, and hydroxy. Analysis based on NMR spectroscopy revealed that the hetero‐ligands on the NCs are well distributed with no ligand segregation. The unprecedented synthesis of multi‐thiolate‐protected Au₂₅ NCs may further promote the practical applications of functional metal NCs.     

Observation of Body‐Centered Cubic Gold Nanocluster

The structure of nanoparticles plays a critical role in dictating their material properties. Gold is well known to adopt face‐centered cubic (fcc) structure. Herein we report the first observation of a body‐centered cubic (bcc) gold nanocluster composed of 38 gold atoms protected by 20 adamantanethiolate ligands and two sulfido atoms ([Au₃₈S₂(SR)₂₀], where R=C₁₀H₁₅) as revealed by single‐crystal X‐ray crystallography. This bcc structure is in striking contrast with the fcc structure of bulk gold and conventional Au nanoparticles, as well as the bi‐icosahedral structure of [Au₃₈(SCH₂CH₂Ph)₂₄]. The bcc nanocluster has a distinct HOMO–LUMO gap of ca. 1.5 eV, much larger than the gap (0.9 eV) of the bi‐icosahedral [Au₃₈(SCH₂CH₂Ph)₂₄]. The unique structure of the bcc gold nanocluster may be promising in catalytic applications.     

Au130−xAgx Nanoclusters with Non‐Metallicity: A Drum of Silver‐Rich Sites Enclosed in a Marks‐Decahedral Cage of Gold‐Rich Sites

The synthesis and structure of atomically precise Au_130?xAg_x (average x=98) alloy nanoclusters protected by 55 ligands of 4‐tert‐butylbenzenethiolate are reported. This large alloy structure has a decahedral M₅₄ (M=Au/Ag) core. The Au atoms are localized in the truncated Marks decahedron. In the core, a drum of Ag‐rich sites is found, which is enclosed by a Marks decahedral cage of Au‐rich sites. The surface is exclusively Ag?SR; X‐ray absorption fine structure analysis supports the absence of Au?S bonds. The optical absorption spectrum shows a strong peak at 523 nm, seemingly a plasmon peak, but fs spectroscopic analysis indicates its non‐plasmon nature. The non‐metallicity of the Au_130?xAg_x nanocluster has set up a benchmark to study the transition to metallic state in the size evolution of bimetallic nanoclusters. The localized Au/Ag binary architecture in such a large alloy nanocluster provides atomic‐level insights into the Au?Ag bonds in bimetallic nanoclusters.     

The Magic Au60 Nanocluster: A New Cluster‐Assembled Material with Five Au13 Building Blocks

Herein, we report the synthesis and atomic structure of the cluster‐assembled [Au₆₀Se₂(Ph₃P)₁₀(SeR)₁₅]⁺ material. Five icosahedral Au₁₃ building blocks from a closed gold ring with Au–Se–Au linkages. Interestingly, two Se atoms (without the phenyl tail) locate in the center of the cluster, stabilized by the Se‐(Au)₅ interactions. The ring‐like nanocluster is unprecedented in previous experimental and theoretical studies of gold nanocluster structures. In addition, our optical and electrochemical studies show that the electronic properties of the icosahedral Au₁₃ units still remain unchanged in the penta‐twinned Au₆₀ nanocluster, and this new material might be a promising in optical limiting material. This work offers a basis for deep understanding on controlling the cluster‐assembled materials for tailoring their functionalities.     

Quasi‐Dual‐Packed‐Kerneled Au49(2,4‐DMBT)27 Nanoclusters and the Influence of Kernel Packing on the Electrochemical Gap

Although face‐centered cubic (fcc), body‐centered cubic (bcc), hexagonal close‐packed (hcp), and other structured gold nanoclusters have been reported, it was unclear whether gold nanoclusters with mix‐packed (fcc and non‐fcc) kernels exist, and the correlation between kernel packing and the properties of gold nanoclusters is unknown. A Au₄₉(2,4‐DMBT)₂₇ nanocluster with a shell electron count of 22 has now been been synthesized and structurally resolved by single‐crystal X‐ray crystallography, which revealed that Au₄₉(2,4‐DMBT)₂₇ contains a unique Au₃₄ kernel consisting of one quasi‐fcc‐structured Au₂₁ and one non‐fcc‐structured Au₁₃ unit (where 2,4‐DMBTH=2,4‐dimethylbenzenethiol). Further experiments revealed that the kernel packing greatly influences the electrochemical gap (EG) and the fcc structure has a larger EG than the investigated non‐fcc structure.