Parasitism in Metal Nanoclusters: A Case Study of (AuAg)25·(AuAg)27.

Studying the interactions of atomically precise metal nanoclusters in their assembly systems is of great significance in the nanomaterial research field, which has attracted increasing interest in the last few decades. Herein, we report the cocrystallization of two oppositely charged atomically precise metal nanoclusters in one unit cell: [Au1Ag24(SR)18]- ((AuAg)25 for short) and [AuxAg27-x(Dppf)4(SR)9]2+ (x = 10-12; (AuAg)27 for short) with a 1:1 ratio. (AuAg)27 could maintain its structure in the presence of (AuAg)25, whether in the crystalline and the solution state, while the metastable (AuAg)27 component underwent a spontaneous transformation to (AuAg)16(Dppf)2(SR)8 after dissociating the (AuAg)25 component from this cocrystal, demonstrating the "parasitism" relationship of the (AuAg)27 component over (AuAg)25 in this dual-cluster system. This work enriches the family of cluster-based assemblies and elucidates the delicate relationship between nanoparticles of cocrystals.

Recent developments in the investigation of driving forces for transforming coinage metal nanoclusters.

Metal nanoclusters serve as an emerging class of modular nanomaterials. The transformation of metal nanoclusters has been fully reflected in their studies from every aspect, including the structural evolution analysis, physicochemical property regulation, and practical application promotion. In this review, we highlight the driving forces for transforming atomically precise metal nanoclusters and summarize the related transforming principles and fundamentals. Several driving forces for transforming nanoclusters are meticulously reviewed herein: ligand-exchange-induced transformations, metal-exchange-induced transformations, intercluster reactions, photochemical transformations, oxidation/reduction-induced transformations, and other factors (intrinsic instability, pH, temperature, and metal salts) triggering transformations. The exploitation of transforming principles to customize the preparations, structures, physicochemical properties, and practical applications of metal nanoclusters is also disclosed. At the end of this review, we provide our perspectives and highlight the challenges remaining for future research on the transformation of metal nanoclusters. Our intended audience is the broader scientific community interested in metal nanoclusters, and we believe that this review will provide researchers with a comprehensive synthetic toolbox and insights on the research fundamentals needed to realize more cluster-based nanomaterials with customized compositions, structures, and properties.

Probing the surface-active sites of metal nanoclusters with atomic precision: a case study of Au5Ag11.

The determination of surface-active sites in metal nanoclusters is of great significance for the in-depth understanding of structural evolutions and physicochemical property mechanisms. In this work, the surface-active sites of the Au5Ag11(DMBT)8(DPPOE)2 cluster template towards metal-/ligand-exchange reactions were unambiguously identified at the atomic level. The active-site tailoring of this nanocluster gave rise to three derivative nanoclusters, Au5Ag9Cu2(DMBT)8(DPPOE)2, Au5Ag11(DMBT)6(DCBT)2(DPPOE)2, and Au5Ag11(DCBT)8(DPPOE)2. The single-crystal structural analysis revealed that all these M16 (M = Au/Ag/Cu) clusters exhibited almost the same framework. Besides, the surface-active site tailoring contributed to significant changes in optical absorptions and emissions of these metal nanoclusters. The findings in this work not only provide an in-depth understanding of the active-site tailoring of cluster surface structures but also develop an intriguing template that enables us to grasp the structure-property correlations at the atomic level.

Structure Determination of the Cl-Enriched [Ag52(SAdm)31Cl13]2+ Nanocluster.

Cl atoms can serve as the innermost core, the peripheral ligand, or the counterions of metal nanoclusters. Herein, we report the structural determination a Cl-enriched [Ag52(SAdm)31Cl13]2+. The ratio of Cl to AdmSH is quite high compared to those of other nanoclusters. Structurally, nine Cl atoms, existing at the interlayer of the inner kernel and the surface motif, serve as the bridging ligands to sustain the robustness of the whole structure. Interestingly, four Cl atoms on the motif structure can be substituted by Br. This work allows us to clear the regulation of Cl ligands in the structural construction of metal nanoclusters.

New atomically precise M1Ag21 (M = Au/Ag) nanoclusters as excellent oxygen reduction reaction catalysts.

By introducing 1,1'-bis-(diphenylphosphino)ferrocene (dppf) as an activating ligand, two novel nanoclusters, M1Ag21 (M = Au/Ag), have been controllably synthesized and structurally characterized. The atomically precise structures of the M1Ag21 nanoclusters were determined by SCXC and further confirmed by ESI-TOF-MS, TGA, XPS, DPV, and FT-IR measurements. The M1Ag21 nanoclusters supported on activated carbon (C) are exploited as efficient oxygen reduction reaction (ORR) catalysts in alkaline solutions. Density functional theory (DFT) calculations verify that the catalytic activities of the two cluster-based systems originate from the significant ensemble synergy effect between the M13 kernel and dppf ligand in M1Ag21. This work sheds lights on the preparation of cluster-based electrocatalysts and other catalysts that are activated and modified by peripheral ligands.

Overall Structures of Two Metal Nanoclusters: Chloride as a Bridge Fills the Space between the Metal Core and the Metal Shell.

In addition to using common ligands (phosphine, thiol, or acetylene ligands) to protect metal nanoclusters, halogens can also be used to participate in the formation of nanoclusters. In this study, we reported the formation of two new nanoclusters promoted by chlorides released from HAuCl4: one [Au1Ag26(SR)18Cl] with an icosahedral Au1Ag12 kernel, which is surrounded by the shell of Ag14(SR)18, and the special chlorine atom fills the space between the metal core and the metal shell; the other [Au6Ag33(Dppf)2(SR)16Cl6]+ with the kernel consisted of two icosahedral Au3Ag10 units by sharing one vertex Ag atom, which is protected by the complicated shell of Ag14(Dppf)2(SR)16Cl4, two special chlorine atoms also fill the space between the metal core and the metal shell. Thus, both two nanoclusters suggest that the chlorine atoms can exist in the space between the metal kernel and out shell, playing a critical role in maintaining the stability of the overall structures. These will deepen the comprehensive understanding of chlorine in constructing the structures of alloy nanoclusters and will also be helpful in mapping out the new strategies for core-shell nanocluster synthesis.

Doping Copper Atoms into the Nanocluster Kernel: Total Structure Determination of [Cu30Ag61(SAdm)38S3](BPh4).

Doping active metal (i.e., Cu) into the kernel of noble metal nanoclusters (i.e., Au/Ag nanocluster) remains challenging in the synthesis of alloy nanoclusters. Herein, we report the synthesis and the total structure determination of a bimetallic [Ag61Cu30(SAdm)38S3]BPh4 (Ag61Cu30) nanocluster. The Ag61Cu30 nanocluster is composed of an Ag13@Cu30 kernel which is further capped by a peripheral Ag48(SAdm)38S3 shell. The icosidodecahedron Cu30 middle layer connects the innermost icosahedral Ag13 core and Ag atoms at the outermost Ag48(SR)38S3 shell, demonstrating that the Cu atoms in the Cu30 layer are in a metallic state.

Bonding of Two 8-Electron Superatom Clusters.

We report the observation of dimerization of two 8-electron superatom cluster units in the crystallographic structures of Au2 Ag42 (SAdm)27 (BPh4 ) and [Au2 Ag48 (S-t Bu)20 (Dppm)6 Br11 ]Br(BPh4 )2 nanoclusters. The crystallographic analysis reveals that both nanoclusters have a Au2 Ag24 core made of two separated icosahedral without sharing metal atoms, and each icosahedron has an eight-electron (8e) closed shell (1S2 1P6 ). The valence electronic structures of these two nanoclusters are analogous to that of a Ne atom dimer (Ne2 ) according to the density functional theory (DFT) analysis. This is the first crystallographic observation of the dimerization of 8-electron superatom units. This study enriches the fundamental knowledge on metal superatom clusters and implies the possibility for further assembling metal superatom building blocks into higher order superatom molecules.

Aggregation-Induced Emission (AIE) in Ag-Au Bimetallic Nanocluster.

Herein we report the synthesis and structure determination of a non-fluorescent Au4 Ag5 (dppm)2 (SAdm)6 (BPh4 ) (dppm=bis(diphenylphosphino)methane and HSAdm=1-adamantane mercaptan) nanocluster in methanol with extremely strong AIE when aggregating to the solid state (i.e., film or crystal). This phenomenon was rarely reported in structural determined noble metal nanoclusters. The extended X-ray absorption fine structure (EXAFS) measurement ruled out the hypothesis that the luminescence originated from the structure change in different states. Besides, the crystal structure (determined by X-ray diffraction) revealed that the tightly combined left- and right-handed enantiomers induced the strong restriction of intramolecular motions (RIM), which may have an impact on aggregation-induced emission.

Multi-ligand-directed synthesis of chiral silver nanoclusters.

Engineering the surface ligands of metal nanoclusters is critical for tuning their sizes, structures and properties at the atomic level. Herein, we report the synthesis and total structure determination of [Ag32(Dppm)5(SAdm)13Cl8]3+ and [Ag45(Dppm)4(S-But)16Br12]3+ (where Dppm = bis(diphenyphosphino)methane, HSAdm = 1-adamantanethiol and HS-But = tert-butyl mercaptan). The compositions of these two silver nanoclusters are determined by single-crystal X-ray diffraction (SC-XRD) and X-ray photoelectron spectroscopy (XPS), respectively. Remarkably, the asymmetric distribution of the three types of ligands (thiolate, phosphine, and halogen) on the cluster surface is responsible for the chirality of the clusters. It is worth noting that these findings demonstrate the key principles of ligand-shell anchoring for the tri-ligand protected silver clusters. Our work will offer further insights into the synthesis of chiral metal clusters by tailoring the surface ligands.

Thiol-Induced Synthesis of Phosphine-Protected Gold Nanoclusters with Atomic Precision and Controlling the Structure by Ligand/Metal Engineering.

Efficient synthesis of atomically precise phosphine-capped gold nanocluster (with >10 metal atoms) is important to deeply understand the relationship between structure and properties. Herein, we successfully utilize the thiol-induced synthesis method and obtain three atomically precise phosphine-protected gold nanoclusters. Single-crystal X-ray structural analysis reveals that the nanoclusters are formulated as [Au13(Dppm)6](BPh4)3, [Au18(Dppm)6Br4](BPh4)2, and [Au20(Dppm)6(CN)6] (where Dppm stands for bis(diphenylphosphino)methane), which are further confirmed by electrospray ionization mass spectrometry, thermogravimetric analysis, and X-ray photoelectron spectroscopy. Meanwhile, [Au18(Dppm)6Br4](BPh4)2 could be converted into [Au13(Dppm)6](BPh4)3 and [Au20(Dppm)6(CN)6] by engineering the surface ligands under excess PPh3 or moderate NaBH3CN, respectively. Furthermore, according to the different binding ability of silver with halogen, we successfully achieved target metal exchange on [Au18(Dppm)6Br4](BPh4)2 with Ag-SAdm (where HS-Adm stands for 1-adamantane mercaptan) complex and obtained [AgxAu18-x(Dppm)6Br4](BPh4)2 (x = 1, 2) alloy nanoclusters. Our work will contribute to more intensive understanding on synthesizing phosphine-protected nanoclusters as well as shedding light on the structure-property correlations in the nanocluster range.

Ag50(Dppm)6(SR)30 and Its Homologue AuxAg50-x(Dppm)6(SR)30 Alloy Nanocluster: Seeded Growth, Structure Determination, and Differences in Properties.

A large thiolate/phosphine coprotected Ag50(Dppm)6(SR)30 nanocluster was synthesized through the further growth of Ag44(SR)30 nanocluster and characterized by X-ray photoelectron spectroscopy (XPS), electrospray ionization mass spectrometry (ESI-MS), and single-crystal X-ray analysis. This new nanocluster comprised a 32-metal-atom dodecahedral kernel and two symmetrical Ag9(SR)15P6 ring motifs. The 20 valence electrons correspond to shell closure in the Jellium model. Moreover, this nanocluster could be alloyed by templated/galvanic metal exchange to the homologue AuxAg50-x(Dppm)6(SR)30 nanocluster; the latter showed much higher thermal stability than the Ag50(Dppm)6(SR)30 nanocluster. Further experiments were conducted to study the optical, electrical, and photoluminescence properties of both nanoclusters. Our work not only reports two new larger size nanoclusters but also reveals a new way to synthesize larger size silver and alloy nanoclusters, that is, controlled growth/alloying.