Huayan Yang

All-thiol-stabilized Ag44 and Au12Ag32 nanoparticles with single-crystal structures

Noble metal nanoparticles stabilized by organic ligands are important for applications in assembly, site-specific bioconjugate labelling and sensing, drug delivery and medical therapy, molecular recognition and molecular electronics, and catalysis. Here we report crystal structures and theoretical analysis of three Ag44(SR)30 and three Au12Ag32(SR)30 intermetallic nanoclusters stabilized with fluorinated arylthiols (SR=SPhF, SPhF2 or SPhCF3). The nanocluster forms a Keplerate solid of concentric icosahedral and dodecahedral atom shells, protected by six Ag2(SR)5 units. Positive counterions in the crystal indicate a high negative charge of 4(-) per nanoparticle, and density functional theory calculations explain the stability as an 18-electron superatom shell closure in the metal core. Highly featured optical absorption spectra in the ultraviolet-visible region are analysed using time-dependent density functional perturbation theory. This work forms a basis for further understanding, engineering and controlling of stability as well as electronic and optical properties of these novel nanomaterials.

Interfacial electronic effects control the reaction selectivity of platinum catalysts

Tuning the electronic structure of heterogeneous metal catalysts has emerged as an effective strategy to optimize their catalytic activities. By preparing ethylenediamine-coated ultrathin platinum nanowires as a model catalyst, here we demonstrate an interfacial electronic effect induced by simple organic modifications to control the selectivity of metal nanocatalysts during catalytic hydrogenation. This we apply to produce thermodynamically unfavourable but industrially important compounds, with ultrathin platinum nanowires exhibiting an unexpectedly high selectivity for the production of N-hydroxylanilines, through the partial hydrogenation of nitroaromatics. Mechanistic studies reveal that the electron donation from ethylenediamine makes the surface of platinum nanowires highly electron rich. During catalysis, such an interfacial electronic effect makes the catalytic surface favour the adsorption of electron-deficient reactants over electron-rich substrates (that is, N-hydroxylanilines), thus preventing full hydrogenation. More importantly, this interfacial electronic effect, achieved through simple organic modifications, may now be used for the optimization of commercial platinum catalysts.

Structural Evolution of Atomically Precise Thiolated Bimetallic [Au12+nCu32(SR)(30+n)](4-) (n=0, 2, 4, 6) Nanoclusters

A series of all-thiol stabilized bimetallic Au-Cu nanoclusters, [Au(12+n)Cu32(SR)(30+n)](4-) (n = 0, 2, 4, 6 and SR = SPhCF3), are successfully synthesized and characterized by X-ray single-crystal analysis and density functional theory (DFT) calculations. Each cluster consists of a Keplerate two-shell Au12@Cu20 core protected by (6 - n) units of Cu2(SR)5 and n units of Cu2Au(SR)6 (n = 0, 2, 4, 6) motifs on its surface. The size and structural evolution of the clusters is atomically controlled by the Au precursors and countercations used in the syntheses. The clusters exhibit similar optical absorption properties that are not dependent on the number of surface Cu2Au(SR)6 units. Although DFT suggests an electronic structure with an 18-electron superatom shell closure, the clusters display different thermal stabilities. [Au(12+n)Cu32(SR)(30+n)](4-) clusters with n = 0 and 2 are more stable than those with n = 4 and 6. Moreover, an oxidation product of the clusters, [Au13Cu12(SR)20](4-), is structurally identified to gain insight into how the clusters are oxidized.

Total Structure and Electronic Structure Analysis of Doped Thiolated Silver [MAg24(SR)18]2– (M = Pd, Pt) Clusters

With the incorporation of Pd or Pt atoms, thiolated Ag-rich 25-metal-atom nanoclusters were successfully prepared and structurally characterized for the first time. With a composition of [PdAg24(SR)18](2-) or [PtAg24(SR)18](2-), the obtained 25-metal-atom nanoclusters have a metal framework structure similar to that of widely investigated Au25(SR)18. In both clusters, a M@Ag12 (M = Pd, Pt) core is capped by six distorted dimeric -RS-Ag-SR-Ag-SR- units. However, the silver-thiolate overlayer gives rise to a geometric chirality at variance to Au25(SR)18. The effect of doping on the electronic structure was studied through measured optical absorption spectra and ab initio analysis. This work demonstrates that modulating electronic structures by transition-metal doping is expected to provide effective means to manipulate electronic, optical, chemical, and catalytic properties of thiolated noble metal nanoclusters.

Ligand-Stabilized Au13Cux (x = 2, 4, 8) Bimetallic Nanoclusters: Ligand Engineering to Control the Exposure of Metal Sites

Three novel bimetallic Au-Cu nanoclusters stabilized by a mixed layer of thiolate and phosphine ligands bearing pyridyl groups are synthesized and fully characterized by X-ray single crystal analysis and density functional theory computations. The three clusters have an icosahedral Au13 core face-capped by two, four, and eight Cu atoms, respectively. All face-capping Cu atoms in the clusters are triply coordinated by thiolate or pyridyl groups. The surface ligands control the exposure of Au sites in the clusters. In the case of the Au13Cu8 cluster, the presence of 12 2-pyridylthiolate ligands still leaves open space for catalysis. All the 3 clusters are 8-electron superatoms displaying optical gaps of 1.8-1.9 eV. The thermal decomposition studies suggest that the selective release of organic ligands from the clusters is possible.

Plasmonic twinned silver nanoparticles with molecular precision

Determining the structures of nanoparticles at atomic resolution is vital to understand their structure–property correlations. Large metal nanoparticles with core diameter beyond 2 nm have, to date, eluded characterization by single-crystal X-ray analysis. Here we report the chemical syntheses and structures of two giant thiolated Ag nanoparticles containing 136 and 374 Ag atoms (that is, up to 3 nm core diameter). As the largest thiolated metal nanoparticles crystallographically determined so far, these Ag nanoparticles enter the truly metallic regime with the emergence of surface plasmon resonance. As miniatures of fivefold twinned nanostructures, these structures demonstrate a subtle distortion within fivefold twinned nanostructures of face-centred cubic metals. The Ag nanoparticles reported in this work serve as excellent models to understand the detailed structure distortion within twinned metal nanostructures and also how silver nanoparticles can span from the molecular to the metallic regime.

Shape-Controlled Synthesis of Surface-Clean Ultrathin Palladium Nanosheets by Simply Mixing a Dinuclear Pd-I Carbonyl Chloride Complex with H2O

通讯作者地址: Zheng, NF (通讯作者) Xiamen Univ, State Key Lab Phys Chem Solid Surfaces, Collaborat Innovat Ctr Chem Energy Mat, Xiamen 361005, Peoples R China.

Electrostatic Self-Assembling Formation of Pd Superlattice Nanowires from Surfactant-Free Ultrathin Pd Nanosheets

A facile method has been developed for face-to-face assembly of two-dimensional surfactant-free Pd nanosheets into one-dimensional Pd superlattice nanowires. The length of the Pd nanowires can be well controlled by introducing cations of different concentration and charge density. Our studies reveal that cations with higher charge density have stronger charge-screening ability, and their introduction leads to more positive zeta-potential and decreased electrostatic repulsion between negatively charged Pd nanosheets. Moreover, their surfactant-free feature is of great importance in assembling the Pd nanosheets into superlattice nanowires. While the cations are important for the assembly of Pd nanosheets, the use of poly(vinylpyrrolidone) is necessary to enhance the stability of the assembled superlattice nanowires. The as-assembled segmented Pd nanowires display tunable surface plasmon resonance features and excellent hydrogen-sensing properties.

Assembled molecular face-rotating polyhedra to transfer chirality from two to three dimensions

In nature, protein subunits on the capsids of many icosahedral viruses form rotational patterns, and mathematicians also incorporate asymmetric patterns into faces of polyhedra. Chemists have constructed molecular polyhedra with vacant or highly symmetric faces, but very little is known about constructing polyhedra with asymmetric faces. Here we report a strategy to embellish a C3h truxene unit with rotational patterns into the faces of an octahedron, forming chiral octahedra that exhibit the largest molar ellipticity ever reported, to the best of our knowledge. The directionalities of the facial rotations can be controlled by vertices to achieve identical rotational directionality on each face, resembling the homo-directionality of virus capsids. Investigations of the kinetics and mechanism reveal that non-covalent interaction among the faces is essential to the facial homo-directionality.

From Racemic Metal Nanoparticles to Optically Pure Enantiomers in One Pot

A general strategy, using mixed ligands, is utilized to synthesize atomically precise, intrinsically chiral nanocluster [Ag78(DPPP)6(SR)42] (Ag78) where DPPP is the achiral 1,3-bis(diphenyphosphino)propane and SR = SPhCF3. Ag78 crystallizes as racemates in a centric space group. Using chiral diphosphines BDPP = 2,4-bis(diphenylphosphino)pentane, the enantiomeric pair [Ag78(R/S-BDPP)6(SR)42] can be prepared with 100% optical purity. The chiral diphosphines gives rise to, separately, two asymmetric surface coordination motifs composed of tetrahedral R3PAg(SR)3 moieties. The flexible nature of C-C-C angles between the two phosphorus atoms restricts the relative orientation of the tetrahedral R3PAg(SR)3 moieties, thereby resulting in the enantiomeric selection of the intrinsic chiral metal core. This proof-of-concept strategy raises the prospect of enantioselectively synthesizing optically pure, atomically precise chiral noble metal nanoclusters for specific applications.