Metal nanoclusters whose surface ligands are removable while keeping their metal framework structures intact are an ideal system for investigating the influence of surface ligands on catalysis of ...metal nanoparticles. We report in this work an intermetallic nanocluster containing 62 metal atoms, Au34Ag28(PhCC)34, and its use as a model catalyst to explore the importance of surface ligands in promoting catalysis. As revealed by single-crystal diffraction, the 62 metal atoms in the cluster are arranged as a four-concentric-shell Ag@Au17@Ag27@Au17 structure. All phenylalkynyl (PA) ligands are linearly coordinated to the surface Au atoms with staple “PhCC–Au–CCPh” motif. Compared with reported thiolated metal nanoclusters, the surface PA ligands on Au34Ag28(PhCC)34 are readily removed at relatively low temperatures, while the metal core remains intact. The clusters before and after removal of surface ligands are used as catalysts for the hydrolytic oxidation of organosilanes to silanols. It is, for the first time, demonstrated that the organic-capped metal nanoclusters work as active catalysts much better than those with surface ligands partially or completely removed.
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Copper–hydrides are known catalysts for several technologically important reactions such as hydrogenation of CO, hydroamination of alkenes and alkynes, and chemoselective hydrogenation of unsaturated ...ketones to unsaturated alcohols. Stabilizing copper-based particles by ligand chemistry to nanometer scale is an appealing route to make active catalysts with optimized material economy; however, it has been long believed that the ligand–metal interface, particularly if sulfur-containing thiols are used as stabilizing agent, may poison the catalyst. We report here a discovery of an ambient-stable thiolate-protected copper–hydride nanocluster Cu25H10(SPhCl2)183– that readily catalyzes hydrogenation of ketones to alcohols in mild conditions. A full experimental and theoretical characterization of its atomic and electronic structure shows that the 10 hydrides are instrumental for the stability of the nanocluster and are in an active role being continuously consumed and replenished in the hydrogenation reaction. Density functional theory computations suggest, backed up by the experimental evidence, that the hydrogenation takes place only around a single site of the 10 hydride locations, rendering the Cu25H10(SPhCl2)183– one of the first nanocatalysts whose structure and catalytic functions are characterized fully to atomic precision. Understanding of a working catalyst at the atomistic level helps to optimize its properties and provides fundamental insights into the controversial issue of how a stable, ligand-passivated, metal-containing nanocluster can be at the same time an active catalyst.
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Gold nanoclusters protected by a thiolate monolayer (MPC) are widely studied for their potential applications in site-specific bioconjugate labeling, sensing, drug delivery, and molecular ...electronics. Several MPCs with 1–2 nm metal cores are currently known to have a well-defined molecular structure, and they serve as an important link between molecularly dispersed gold and colloidal gold to understand the size-dependent electronic and optical properties. Here, we show by using an ab initio method together with atomistic models for experimentally observed thiolate-stabilized gold clusters how collective electronic excitations change when the gold core of the MPC grows from 1.5 to 2.0 nm. A strong localized surface plasmon resonance (LSPR) develops at 540 nm (2.3 eV) in a cluster with a 2.0 nm metal core. The protecting molecular layer enhances the LSPR, while in a smaller cluster with 1.5 nm gold core, the plasmon-like resonance at 540 nm is confined in the metal core by the molecular layer. Our results demonstrate a threshold size for the emergence of LSPR in these systems and help to develop understanding of the effect of the molecular overlayer on plasmonic properties of MPCs enabling engineering of their properties for plasmonic applications.
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An intermetallic nanocluster containing 44 metal atoms, Au24Ag20(2-SPy)4(PhCC)20Cl2, was successfully synthesized and structurally characterized by single-crystal analysis and density funtional ...theory computations. The 44 metal atoms in the cluster are arranged as a concentric three-shell Au12@Ag20@Au12 Keplerate structure having a high symmetry. For the first time, the co-presence of three different types of anionic ligands (i.e., phenylalkynyl, 2-pyridylthiolate, and chloride) was revealed on the surface of metal nanoclusters. Similar to thiolates, alkynyls bind linearly to surface Au atoms using their σ-bonds, leading to the formation of two types of surface staple units (PhCC-Au-L, L = PhCC– or 2-pyridylthiolate) on the cluster. The co-presence of three different surface ligands allows the site-specific surface and functional modification of the cluster. The lability of PhCC– ligands on the cluster was demonstrated, making it possible to keep the metal core intact while removing partial surface capping. Moreover, it was found that ligand exchange on the cluster occurs easily to offer various derivatives with the same metal core but different surface functionality and thus different solubility.
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We report on how the transition from the bulk structure to the cluster-specific structure occurs in n-dodecanethiolate-protected gold clusters, Au n (SC12) m . To elucidate this transition, we ...isolated a series of Au n (SC12) m in the n range from 38 to ∼520, containing five newly identified or newly isolated clusters, Au104(SC12)45, Au∼226(SC12)∼76, Au∼253(SC12)∼90, Au∼356(SC12)∼112, and Au∼520(SC12)∼130, using reverse-phase high-performance liquid chromatography. Low-temperature optical absorption spectroscopy, powder X-ray diffractometry, and density functional theory (DFT) calculations revealed that the Au cores of Au144(SC12)60 and smaller clusters have molecular-like electronic structures and non-fcc geometric structures, whereas the structures of the Au cores of larger clusters resemble those of the bulk gold. A new structure model is proposed for Au104(SC12)45 based on combined approach between experiments and DFT calculations.
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Magic-number gold nanoclusters are atomically precise nanomaterials that have enabled unprecedented insight into structure-property relationships in nanoscience. Thiolates are the most common ligand, ...binding to the cluster via a staple motif in which only central gold atoms are in the metallic state. The lack of other strongly bound ligands for nanoclusters with different bonding modes has been a significant limitation in the field. Here, we report a previously unknown ligand for gold(0) nanoclusters-N-heterocyclic carbenes (NHCs)-which feature a robust metal-carbon single bond and impart high stability to the corresponding gold cluster. The addition of a single NHC to gold nanoclusters results in significantly improved stability and catalytic properties in the electrocatalytic reduction of CO
. By varying the conditions, nature and number of equivalents of the NHC, predominantly or exclusively monosubstituted NHC-functionalized clusters result. Clusters can also be obtained with up to five NHCs, as a mixture of species.
This paper reports co-crystallization of two atomically precise, different-size ligand-stabilized nanoclusters, a spherical (AuAg)
(SR)
and a smaller trigonal-prismatic (AuAg)
(SR)
(PPh
)
in 1:1 ...ratio, characterized fully by X-ray crystallographic analysis (SR = 2,4-SPhMe
). The larger cluster has a four concentric-shell icosahedral structure of Ag@M
@M
@M
@Ag
(SR)
(M = Au or Ag) with the inner-core M
icosahedron observed here for metal nanoparticles. The cluster has an open electron shell of 187 delocalized electrons, fully metallic, plasmonic behavior, and a zero HOMO-LUMO energy gap. The smaller cluster has an 18-electron shell closing, a notable HOMO-LUMO energy gap and a molecule-like optical spectrum. This is the first direct demonstration of the simultaneous presence of competing effects (closing of atom vs. electron shells) in nanocluster synthesis and growth, working together to form a co-crystal of different-sized clusters. This observation suggests a strategy that may be helpful in the design of other nanocluster systems via co-crystallization.
Demonstrated herein are the preparation and crystallographic characterization of the family of fcc silver nanoclusters from Nichol’s cube to Rubik’s cube and beyond via ligand-control (thiolates and ...phosphines in this case). The basic building block is our previously reported fcc cluster Ag14(SPhF2)12(PPh3)8 (1). The metal frameworks of Ag38(SPhF2)26(PR′3)8 (2 2 ) and Ag63(SPhF2)36(PR′3)8+ (2 3 ), where HSPhF2 = 3,4-difluorothiophenol and R′ = alkyl/aryl, are composed of 2 × 2 = 4 and 2 × 2 × 2 = 8 metal cubes of 1, respectively. All serial clusters share similar surface structural features. The thiolate ligands cap the six faces and the 12 edges of the cube (or half cube) while the phosphine ligands are terminally bonded to its eight corners. On the basis of the analysis of the crystal structures of 1, 2 2 , and 2 3 , we predict the next “cube of cubes” to be Ag172(SR)72(PR′3)8 (3 3 ), in the evolution of growth of this cluster sequence.
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Density-functional theory computations on a cluster Au144(SR)60 with an icosahedral Au114 core with 30 RS−Au−SR units protecting its surface yield an excellent fit of the structure factor to the ...experimental X-ray scattering structure factor measured earlier for 29 kDa thiolate-protected gold clusters. This cluster has a special combination of atomic and electronic structure that provides explanations for the observed stability and capacitive charging properties with several available oxidation states in electrochemistry and optical absorption extending well into the infrared region.
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Thiolate-protected gold surfaces and interfaces, relevant for self-assembled monolayers of organic molecules on gold, for passivated gold nanoclusters and for molecule-gold junctions, are archetypal ...systems in various fields of current nanoscience research, materials science, inorganic chemistry and surface science. Understanding this interface at the nanometre scale is essential for a wide range of potential applications for site-specific bioconjugate labelling and sensing, drug delivery and medical therapy, functionalization of gold surfaces for sensing, molecular recognition and molecular electronics, and gold nanoparticle catalysis. During the past five years, considerable experimental and theoretical advances have furthered our understanding of the molecular structure of the gold-sulfur interface in these systems. This Review discusses the recent progress from the viewpoint of theory and computations, with connections to relevant experiments.
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