Templated Atom‐Precise Galvanic Synthesis and Structure Elucidation of a [Ag24Au(SR)18]− Nanocluster

Synthesis of atom‐precise alloy nanoclusters with uniform composition is challenging when the alloying atoms are similar in size (for example, Ag and Au). A galvanic exchange strategy has been devised to produce a compositionally uniform [Ag₂₄Au(SR)₁₈]^? cluster (SR: thiolate) using a pure [Ag₂₅(SR)₁₈]^? cluster as a template. Conversely, the direct synthesis of Ag₂₄Au cluster leads to a mixture of [Ag_25?xAu_x(SR)₁₈]^?, x=1–8. Mass spectrometry and crystallography of [Ag₂₄Au(SR)₁₈]^? reveal the presence of the Au heteroatom at the Ag₂₅ center, forming Ag₂₄Au. The successful exchange of the central Ag of Ag₂₅ with Au causes perturbations in the Ag₂₅ crystal structure, which are reflected in the absorption, luminescence, and ambient stability of the particle. These properties are compared with those of Ag₂₅ and Ag₂₄Pd clusters with same ligand and structural framework, providing new insights into the modulation of cluster properties with dopants at the single‐atom level.     

Structure of the Au23−xAgx(S‐Adm)15 Nanocluster and Its Application for Photocatalytic Degradation of Organic Pollutants

Ligands play an important role in determining the atomic arrangement within the metal nanoclusters. Here, we report a new nanocluster [Au_23?xAg_x(S‐Adm)₁₅] protected by bulky adamantanethiol ligands which was obtained through a one‐pot synthesis. The total structure of [Au_23?xAg_x(S‐Adm)₁₅] comprises an Au_13?xAg_x icosahedral core, three Au₃(SR)₄ units, and one AgS₃ staple motif in contrast to the 15‐atom bipyramidal core previously seen in [Au_23?xAg_x(SR)₁₆]. UV/Vis spectroscopy indicates that the HOMO–LUMO gap of [Au_23?xAg_x(S‐Adm)₁₅] is 1.5 eV. DFT calculations reveal that [Au₁₉Ag₄(S‐Adm)₁₅] is the most stable structure among all structural possibilities. Benefitting from Ag doping, [Au_23?xAg_x(S‐Adm)₁₅] exhibits drastically improved photocatalytic activity for the degradation of rhodamine B (RhB) and phenol under visible‐light irradiation compared to Au₂₃ nanoclusters.     

A 200‐fold Quantum Yield Boost in the Photoluminescence of Silver‐Doped AgxAu25−x Nanoclusters: The 13 th Silver Atom Matters

The rod‐shaped Au₂₅ nanocluster possesses a low photoluminescence quantum yield (QY=0.1 %) and hence is not of practical use in bioimaging and related applications. Herein, we show that substituting silver atoms for gold in the 25‐atom matrix can drastically enhance the photoluminescence. The obtained Ag_xAu_25?x (x=1–13) nanoclusters exhibit high quantum yield (QY=40.1 %), which is in striking contrast with the normally weakly luminescent Ag_xAu_25?x species (x=1–12, QY=0.21 %). X‐ray crystallography further determines the substitution sites of Ag atoms in the Ag_xAu_25?x cluster through partial occupancy analysis, which provides further insight into the mechanism of photoluminescence enhancement.     

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.     

Aurophilic Interactions in the Self‐Assembly of Gold Nanoclusters into Nanoribbons with Enhanced Luminescence

Aurophilic interactions (Au^I???Au^I) are crucial in directing the supramolecular self‐assembly of many gold(I) compounds; however, this intriguing chemistry has been rarely explored for the self‐assembly of nanoscale building blocks. Herein, we report on studies on aurophilic interactions in the structure‐directed self‐assembly of ultrasmall gold nanoparticles or nanoclusters (NCs, <2 nm) using [Au₂₅(SR)₁₈]^? (SR=thiolate ligand) as a model cluster. The self‐assembly of NCs is initiated by surface‐motif reconstruction of [Au₂₅(SR)₁₈]^? from short SR‐[Au^I‐SR]₂ units to long SR‐[Au^I‐SR]_x (x>2) staples accompanied by structure modification of the intrinsic Au₁₃ kernel. Such motif reconstruction increases the content of Au^I species in the protecting shell of Au NCs, providing the structural basis for directed aurophilic interactions, which promote the self‐assembly of Au NCs into well‐defined nanoribbons in solution. More interestingly, the compact structure and effective aurophilic interactions in the nanoribbons significantly enhance the luminescence intensity of Au NCs with an absolute quantum yield of 6.2 % at room temperature.     

Revealing the composition-dependent structural evolution fundamentals of bimetallic nanoparticles through an inter-particle alloying reaction

Alloy nanoparticles represent one of the most important metal materials, finding increasing applications in diverse fields of catalysis, biomedicine, and nano-optics. However, the structural evolution of bimetallic nanoparticles in their full composition spectrum has been rarely explored at the molecular and atomic levels, imparting inherent difficulties to establish a reliable structure–property relationship in practical applications. Here, through an inter-particle reaction between [Au₄₄(SR)₂₆]²⁻ and [Ag₄₄(SR)₃₀]⁴⁻ nanoparticles or nanoclusters (NCs), which possess the same number of metal atoms, but different atomic packing structures, we reveal the composition-dependent structural evolution of alloy NCs in the alloying process at the molecular and atomic levels. In particular, an inter-cluster reaction can produce three sets of Au_xAg_44−x NCs in a wide composition range, and the structure of Au_xAg_44−x NCs evolves from Ag-rich [Au_xAg_44−x(SR)₃₀]⁴⁻ (x = 1–12), to evenly mixed [Au_xAg_44−x(SR)₂₇]³⁻ (x = 19–24), and finally to Au-rich [Au_xAg_44−x(SR)₂₆]²⁻ (x = 40–43) NCs, with the increase of the Au/Ag atomic ratio in the NC composition. In addition, leveraging on real-time electrospray ionization mass spectrometry (ESI-MS), we reveal the different inter-cluster reaction mechanisms for the alloying process in the sub-3-nm regime, including partial decomposition–reconstruction and metal exchange reactions. The molecular-level inter-cluster reaction demonstrated in this study provides a fine chemistry to customize the composition and structure of bimetallic NCs in their full alloy composition spectrum, which will greatly increase the acceptance of bimetallic NCs in both basic and applied research.

An inter-particle reaction between atomically precise [Au₄₄(SR)₂₆]²⁻ (SR = thiolate) and [Ag₄₄(SR)₃₀]⁴⁻ nanoparticles reveals the composition-dependent structural evolution of alloy Au_xAg_44−x nanoparticles at the atomic level.     

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.     

The Origin of the Photoluminescence Enhancement of Gold‐Doped Silver Nanoclusters: The Importance of Relativistic Effects and Heteronuclear Gold–Silver Bonds

The weak photoluminescence of silver nanoclusters prevents their broad application as luminescent nanomaterials. Recent experiments, however, have shown that gold doping can significantly enhance the photoluminescence intensity of Ag₂₉ nanoclusters but the molecular and physical origins of this effect remain unknown. Therefore, we have computationally explored the geometric and electronic structures of Ag₂₉ and gold‐doped Ag_29?xAu_x (x=1–5) nanoclusters in the S₀ and S₁ states. We found that 1) relativistic effects that are mainly due to the Au atoms play an important role in enhancing the fluorescence intensity, especially for highly doped Ag₂₆Au₃, Ag₂₅Au₄, and Ag₂₄Au₅, and that 2) heteronuclear Au?Ag bonds can increase the stability and regulate the fluorescence intensity of isomers of these gold‐doped nanoclusters. These novel findings could help design doped silver nanoclusters with excellent luminescence properties.     

Exposing the Delocalized Cu−S π Bonds on the Au24Cu6(SPhtBu)22 Nanocluster and Its Application in Ring‐Opening Reactions

Bimetallic nanomaterials are of major importance in catalysis. A Au‐Cu bimetallic nanocluster was synthesized that is effective in catalyzing the epoxide ring‐opening reaction. The catalyst was analyzed by SCXRD and ESI‐MS and found to be Au₂₄Cu₆(SPhtBu)₂₂ (Au₂₄Cu₆ for short). Six copper atoms exclusively occupy the surface positions in two groups with three atoms for each, and each group was bonded with three thiolate ligands to give a planar motif reminiscent of a benzene ring. In the epoxide‐ring opening reaction, Au₂₄Cu₆ exhibited superior catalytic activity compared to other homometallic and Au‐Cu alloy NCs, such as Au₂₅ and Au_38?xCu_x. Control experiments and DFT calculations revealed that the π conjugation among the Cu?S bonds played a pivotal role. This study demonstrates a unique π conjugation established among the Cu?S bonds as a critical structural motif in the nanocluster, which facilitates the catalysis of a ring‐opening reaction.     

Hollow Versus Hydrogen-Occupied Icosahedral Cages of Coinage–Metal Clusters

It is suggested that the hollow coinage–metal icosahedral cage of the [Ag₄₄(SR)₃₀]^4? tetraanion (1a) may be occupied by two hydrogen atoms, giving rise to a dihydridic cluster [H₂Ag₄₄(SR)₃₀]^4? tetraanion (2b). As a consequence, two series of clusters, with different electron counts, can be formed by chemical means: the 18-electron series [H _x Ag₄₄(SR)₃₀]^(4?x)? via stepwise protonation of 1a and the 20-electron series [H _x Ag₄₄(SR)₃₀]^(6?x)? via stepwise deprotonation of 2b (here x = 0, 1, 2). Both series are closed-shell Jelliumatic clusters and expected to be stable. The corresponding members of these two series (for a given x value) are related by a two-electron reduction. These pairs raise the possibility of the hollow icosahedral metal cages in housing a number of hydrogen atoms, either via stepwise protonations or by absorption of hydrogen molecules.     

Low-dimensional Compounds Containing Cyano Groups. XIII. Structural–spectral Correlation of Copper Dicyanoargentates

The new mixed-valence mixed-metal complex Cu(py)₆Cu₂Ag₂(CN)₆ (py = pyridine) possesses a three dimensional polymeric crystal structure. The Cu(I) atom is tetrahedrally coordinated by two nitrogen atoms of pyridine molecules, by one nitrogen atom of the dicyanoargentate anion and by one carbon atom of the cyano group. Both the dicyanoargentate anion and the cyano group bridge the Cu(I) atom with neighboring Cu(II) atoms. These are hexacoordinated in the form of an elongated tetragonal bipyramid. The equatorial plane is formed by two nitrogen atoms from two pyridine molecules and two nitrogen atoms from bridging cyano groups. Axial positions are occupied by nitrogen atoms of the bridging [Ag(CN₂]⁻ anions. Correlation between structures of the title compound and seven other dicyanoargentates with their i.r. spectra has been studied. The coordination mode of [Ag(CN₂]⁻ anions in compounds Cu_8-xAg_x(tn)₃(CN)₁₀ x = 0.25, Cu(3-Mepy)₂Ag₂(CN)₄, Cu(py)₂Ag₂(CN)₄ and Cu(py)₄Ag₂(CN)₄ (tn is 1,3-diaminopropane, 3-Mepy is 3-methylpyridine) is predicted based on this correlation.     

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.     

Ligand‐Stabilized and Atomically Precise Gold Nanocluster Catalysis: A Case Study for Correlating Fundamental Electronic Properties with Catalysis

We present results from our investigations into correlating the styrene‐oxidation catalysis of atomically precise mixed‐ligand biicosahedral‐structure [Au₂₅(PPh₃)₁₀(SC₁₂H₂₅)₅Cl₂]²⁺ (Au₂₅‐bi) and thiol‐stabilized icosahedral core–shell‐structure [Au₂₅(SCH₂CH₂Ph)₁₈]^? (Au₂₅‐i) clusters with their electronic and atomic structure by using a combination of synchrotron radiation‐based X‐ray absorption fine‐structure spectroscopy (XAFS) and ultraviolet photoemission spectroscopy (UPS). Compared to bulk Au, XAFS revealed low Au–Au coordination, Au? Au bond contraction and higher d‐band vacancies in both the ligand‐stabilized Au clusters. The ligands were found not only to act as colloidal stabilizers, but also as d‐band electron acceptor for Au atoms. Au₂₅‐bi clusters have a higher first‐shell Au coordination number than Au₂₅‐i, whereas Au₂₅‐bi and Au₂₅‐i clusters have the same number of Au atoms. The UPS revealed a trend of narrower d‐band width, with apparent d‐band spin–orbit splitting and higher binding energy of d‐band center position for Au₂₅‐bi and Au₂₅‐i. We propose that the differences in their d‐band unoccupied state population are likely to be responsible for differences in their catalytic activity and selectivity. The findings reported herein help to understand the catalysis of atomically precise ligand‐stabilized metal clusters by correlating their atomic or electronic properties with catalytic activity.     

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.     

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.     

EPR‐spektroskopische Charakterisierung (X‐, Q‐Band) monomerer AgII‐ und AuII‐Komplexe der Thiakronenether [12]anS4, [16]anS4, [18]anS6 und [27]anS9

EPR Spectroscopic Characterization (X‐, Q‐Band) of Monomeric Ag^II‐ and Au^II‐Complexes of the Thiacrownethers [12]aneS₄, [16]aneS₄, [18]aneS₆ and [27]aneS₉ The reaction of the prepared Ag^I complexes of the thiacrownethers [12]aneS₄, [16]aneS₄, [18]aneS₆ and [27]aneS₉ with c. H₂SO₄ as well as the reaction of [Au^IIICl₄]^‐ with [18]aneS₆ and [27]aneS₉ leads to labile Ag^II‐ (4d⁹, ^{107, 109}Ag: I=1/2) and Au^II‐ (5d⁹, ¹⁹⁷Au: I=3/2) thiacrownether complexes, respectively, which were characterized by X‐ and Q‐band EPR. The EPR spectra of [Ag^II([12]anS₄)]²⁺ and [Ag^II([18]anS₆)]²⁺ were reinvestigated. According to an analysis of the spin‐density distribution only 20 ‐ 25 % is located on the Ag or Au atoms. Most of the spin‐density was found to be on the S donor atoms of the thiacrownethers. The high delocalization of the spin‐density leads certainly to a noticeable reduction of the Ag^I/Ag^II redox potential and is considered as being mainly responsible for the easy accessibility of the Ag^II compounds.     

Ag2Au50(PET)36 Nanocluster: Dimeric Assembly of Au25(PET)18 Enabled by Silver Atoms

The assembly of atomically precise metal nanoclusters offers exciting opportunities to gain fundamental insights into the hierarchical assembly of nanoparticles. However, it is still challenging to control the assembly of individual nanoclusters at a molecular or atomic level. Herein, we report the dimeric assembly of Au₂₅(PET)₁₈ (PET=2‐phenylethanethiol), where two Au₂₅(PET)₁₈ monomers are bridged together by two Ag atoms to form the Ag₂Au₅₀(PET)₃₆ dimer. The Ag₂Au₅₀(PET)₃₆ dimer is a unique mesomer, which has not been found in any other chiral metal nanoclusters. Furthermore, the Ag₂Au₅₀(PET)₃₆ dimer is distinct from the Au₂₅(PET)₁₈ monomer in its optical, electronic, and catalytic properties. This study is expected to provide a feasible strategy to precisely modulate the assembly of metal nanoclusters with controllable structures and properties.     

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 D₃ 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.

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. It is a 6e system showing quite a different absorption spectrum from [Au₂₅(SR)₁₈]⁻.     

Rapid Conversion of a Au9Ag12 into a AuxAg16-x Nanocluster via Bisphosphine Ligand Engineering

The [Au_xAg_16-x(SAdm)₈(Dppe)₂] nanocluster with aggregation-induced emission (AIE) was synthesized from a non-fluorescent [Au₉Ag₁₂(SAdm)₄(Dppm)₆Cl₆](SbF₆)₃ nanocluster via a ligand-exchange engineering (Dppe=1,2-Bis(diphenylphosphino)ethane, Dppm=Bis(diphenylphosphino)methane, HSAdm=1-Adamantanethiol). The nanocluster has a Au-doped icosahedral Au_xAg_13-x core, capped by two Ag(SR)₃, one Ag(SR)₂ and two Dppe ligands. By changing the achiral Dppe ligand into a chiral dbpb ligand ((2S,3S)-(-)-Bis(diphenylphosphino)butane or (2R,3R)-(+)-2,3-Bis(diphenylphosphino)butane), chiral nanoclusters are obtained. ESI-MS and UV-vis spectroscopy were performed to track the reaction. This work provides guidance for the construction of new clusters by etching clusters with multidentate phosphine ligands.     

Cu掺杂对Au11(dppf)4Cl2纳米团簇结构和光学性质的影响

通过一锅还原法成功制备了合金纳米团簇Au_11-xCu_x(dppf)₄Cl₂(x=1、2;dppf=1,1''-双(二苯基膦)二茂铁)。晶体结构解析表明,合金团簇具有与 Au₁₁(dppf)₄Cl₂类似的几何结构,如含有缺陷二十面体金属内核,不同之处在于 Cu原子取代了与 Cl配位的Au原子。因此,Au_11-xCu_x(dppf)₄Cl₂可视为Cu对Au₁₁(dppf)₄Cl₂模板团簇的掺杂。Cu原子的引入并未改变模板团簇Au₁₁(dppf)₄Cl₂的框架结构,但有效调控了电子结构,进而使其光吸收发生红移。