A vibrational study by Raman spectroscopy of some dinuclear gold ylide complexes

A vibrational study of the dinuclear gold ylide complexes [Au(CH₂)₂PPh₂]₂ and [Au(CH₂)₂PPh₂]₂X₂ (X = Cl, Br or I) has been undertaken by Raman spectroscopy. The non-bonding AuAu interaction in the Au^I dimer, [Au(CH₂)₂PPh₂)₂, at 64 cm⁻¹ shifts to higher wavenumber in the single-bonded Au^II halogen complexes, with bands at 162, 132 and 103 cm⁻¹ for X = Cl, Br and I, respectively, being assigned to ν(AuAu). The Au-X vibration was also identified. The general trends in AuAu and Au-X stretching vibrations with changing halogen are compared with those for other dinuclear metal-metal bonded complexes, with a metal-metal bond order of one, and with those for mononuclear gold-halogen complexes.     

A Tray‐Shaped,PdII‐Clipped Au3 Complex as a Scaffold for the Modular Assembly of [3×n] Au Ion Clusters

A tray‐shaped Pd^II₃Au^I₃ complex ( 1 ) is prepared from 3,5‐bis(3‐pyridyl)pyrazole by means of tricyclization with Au^I followed by Pd^II clipping. Tray 1 is an efficient scaffold for the modular assembly of [3×n] Au^I clusters. Treatment of 1 with the Au^I₃ tricyclic guest 2 in H₂O/CH₃CN (7:3) or H₂O results in the selective formation of a [3×2] cluster ( 1 ? 2 ) or a [3×3] cluster ( 1 ? 2 ? 1 ), respectively. Upon subsequent addition of Ag^I ions, these complexes are converted to an unprecedented Au₃–Au₃–Ag–Au₃–Au₃ metal ion cluster.     

A Tray‐Shaped,PdII‐Clipped Au3 Complex as a Scaffold for the Modular Assembly of [3×n] Au Ion Clusters

A tray‐shaped Pd^II₃Au^I₃ complex ( 1 ) is prepared from 3,5‐bis(3‐pyridyl)pyrazole by means of tricyclization with Au^I followed by Pd^II clipping. Tray 1 is an efficient scaffold for the modular assembly of [3×n] Au^I clusters. Treatment of 1 with the Au^I₃ tricyclic guest 2 in H₂O/CH₃CN (7:3) or H₂O results in the selective formation of a [3×2] cluster ( 1 ⋅ 2 ) or a [3×3] cluster ( 1 ⋅ 2 ⋅ 1 ), respectively. Upon subsequent addition of Ag^I ions, these complexes are converted to an unprecedented Au₃–Au₃–Ag–Au₃–Au₃ metal ion cluster.     

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]⁻.     

Electrochemical CO2 reduction catalyzed by atomically precise alkynyl-protected Au7Ag8, Ag9Cu6, and Au2Ag8Cu5 nanoclusters: probing the effect of multi-metal core on selectivity

Doping metal nanoclusters (NCs) with another metal usually leads to superior catalytic performance toward CO₂ reduction reaction (CO₂RR), yet elucidating the metal core effect is still challenging. Herein, we report the systematic study of atomically precise alkynyl-protected Au₇Ag₈, Ag₉Cu₆, and Au₂Ag₈Cu₅ NCs toward CO₂RR. Au₂Ag₈Cu₅ prepared by a site-specific metal exchange approach from Ag₉Cu₆ is the first case of trimetallic superatom with full-alkynyl protection. The three M₁₅ clusters exhibited drastically different CO₂RR performance. Specifically, Au₇Ag₈ demonstrated high selectivity for CO formation in a wide voltage range (98.1% faradaic efficiency, FE, at −0.49 V and 89.0% FE at −1.20 V vs. RHE), while formation of formate becomes significant for Ag₉Cu₆ and Au₂Ag₈Cu₅ at more negative potentials. DFT calculations demonstrated that the exposed, undercoordinated metal atoms are the active sites and the hydride transfer as well as HCOO* stabilization on the Cu–Ag site plays a critical role in the formate formation. Our work shows that, tuning the metal centers of the ultrasmall metal NCs via metal exchange is very useful to probe the structure–selectivity relationships for CO₂RR.

We report the first all-alkynyl-protected Au₂Ag₈Cu₅ cluster, which adopts a M@M₈@M₆ core configuration similar with Au₇Ag₈/Ag₉Cu₆ clusters. The three clusters exhibited strong metal core effect toward CO₂RR, which was understood by DFT calculations.     

DFT Insights into the Variety in the Coordination Modes of the Equatorial Halides in [Au13Ag12(PR3)10X8]+ (X=Cl/Br) Clusters

The bonding character within metal nanoclusters represents an intriguing topic, shedding light on the inherent driving force for the packing preference in nanomaterials. Herein, density functional theory (DFT) calculations were conducted to investigate the correlation of the series of isomeric [Au₁₃Ag₁₂(PR₃)₁₀X₈]⁺ (X=Cl/Br) clusters, which are mainly differentiated by the coordination mode of the equatorial halides (μ₂-, μ₃- and μ₄-) in the rod-like, bi-icosahedral framework. The theoretical simulation corroborates the variety in the configuration of the Au₁₃Ag₁₂ clusters and elucidates the fast isomerization kinetics among the different configurations. The easy tautomerization and the variety in chloride binding modes correspond to a fluxionality character of the equatorial halides and are verified by the potential energy curve analysis. The structural flexibility of the central Au₃Ag₁₀ block is the main driving force, while the relatively stronger Ag−X bonding interaction (compared to that of Au−X), and a sufficient number of halides are also requisite for the associating Ag−X tautomerizations.     

Heteroctanuclear Au4Ag4 Cluster Complexes of 4,5-Diethynylacridin-9-One with Luminescent Mechanochromism

Two heteroctanuclear Au₄Ag₄ cluster complexes of 4,5-diethynylacridin-9-one (H₂L) were prepared through the self-assembly reactions of [Au(tht)₂](CF₃SO₃), Ag(tht)(CF₃SO₃), H₂L and PPh₃ or PPh₂Py (2-(diphenylphosphino)pyridine). The Au₄Ag₄ cluster consists of a [Au₄L₄]⁴⁻ and four [Ag(PPh₃)]⁺ or [Ag(PPh₂Py)]⁺ units with Au₄L₄ framework exhibiting a twisted paper clip structure. In CH₂Cl₂ solutions at ambient temperature, both compounds show ligand fluorescence at ca. 463 nm as well as phosphorescence at 650 nm for 1 and 630 nm for 2 resulting from admixture of ³IL (intraligand) of L ligand, ³LMCT (from L ligand to Au₄Ag₄) and ³MC (metal-cluster) triplet states. Crystals or crystalline powders manifest bright yellow-green phosphorescence with vibronic-structured emission bands at 530 (568sh) nm for complex 1 and 536 (576sh) nm for complex 2. Upon mechanical grinding, yellow-green emission in the crystalline state is dramatically converted to red luminescence centered at ca. 610 nm with a drastic redshift of the emission after crystal packing is destroyed.     

Biofunctionalization of Polyoxometalates with DNA Primers,Their Use in the Polymerase Chain Reaction (PCR) and Electrochemical Detection of PCR Products

The bioconjugation of polyoxometalates (POMs), which are inorganic metal oxido clusters, to DNA strands to obtain functional labeled DNA primers and their potential use in electrochemical detection have been investigated. Activated monooxoacylated polyoxotungstates [SiW₁₁O₃₉{Sn(CH₂)₂CO}]^8? and [P₂W₁₇O₆₁{Sn(CH₂)₂CO}]^6? have been used to link to a 5′‐NH₂ terminated 21‐mer DNA forward primer through amide coupling. The functionalized primer was characterized by using a battery of techniques, including electrophoresis, mass spectrometry, as well as IR and Raman spectroscopy. The functionality of the POM‐labeled primers was demonstrated through hybridization with a surface‐immobilized probe. Finally, the labeled primers were successfully used in the polymerase chain reaction (PCR) and the PCR products were characterized by using electrophoresis.     

双核Au(I)磷硫配合物激发态性质和金属间弱相互作用的从头算研究

采用MP2和CIS方法分别优化双核Au(I)磷硫配合物, [Au₂(SHCH₂SH)₂]^2＋ (1), [Au₂(SHCH₂SH)(PH₂CH₂PH₂)]^2＋(2), [Au₂(PH₂CH₂PH₂)₂]^2＋ (3), [Au₂(SHCH₂SH)(SCH₂S)] (4), [Au₂(PH₂CH₂PH₂)(SCH₂S)] (5)和[Au₂(SCH₂S)₂]^2－ (6), 基态和激发态的结构. 计算结果表明基态时1～6中存在Au(I)-Au(I)弱吸引作用, 激发态时1～5的金属间相互作用明显增强而6则减弱, 这与实验研究结果一致. 单激发组态相互作用计算揭示: 磷硫配体的更替使得Au(I)配合物跃迁性质呈现MC→MMLCT→MLCT的规律性变化(MC: 金属中心; MMLCT: 金属金属到配体电荷转移; MLCT: 金属到配体电荷转移).     

Coordination/organometallic polymers based on diphosphine and diisocyanide ligands

This paper reviews various coordination/ organometallic polymers in which the metal atoms are incorporated in the backbone using diphosphine and diisocyanide ligands. Such ligands includes diphosphines of the type bis(diphenylphosphino)alkane where alkane is (CH₂)_m with m = 1, 3-6, bis(diphenylphosphino)acetylene (dpa), and bis(dimethylphosphino)methane (dmpm), and diisocyanides such as 1,8-diiso-cyano-p-menthane (dmb) and p-diisocyanotetra-methylbenzene (ditmb). The metal fragments are monocations such as Cu⁺, Ag⁺, and Au⁺, dinuclear species such as Pd₂(dmb)₂²⁺, Pd₂(dppm)₂²⁺, M₂(dmpm)₃²⁺ (M = Cu, Ag), and clusters such as M₄(dmb)₄²⁺ (M = Pd, Pt).     

Small Gold(I) and Gold(I)–Silver(I) Clusters by C−Si Auration

Auration of o-trimethylsilyl arylphosphines leads to the formation of gold and gold–silver clusters with ortho-metalated phosphines displaying 3c–2e Au−C−M bonds (M=Au/Ag). Hexagold clusters [Au₆L₄](X)₂ are obtained by reaction of (L−TMS)AuCl with AgX, whereas reaction with AgX and Ag₂O leads to gold–silver clusters [Au₄Ag₂L₄](X)₂. Oxo-trigold(I) species [Au₃O]⁺ were identified as the intermediates in the formation of the silver-doped clusters. Other [Au₅], [Au₄Ag], and [Au₁₂Ag₄] clusters were also obtained. Clusters containing PAu−Au−AuP structural motif display good catalytic activity in the activation of alkynes under homogeneous conditions.     

Solvation and lon association in the system AgNO3−CH3CN: A Raman and infrared spectral study

Detailed studies of the Raman and infrared line parameters of AgNO₃?CH₃CN systems ranging from dilute solutions to 9M are reported. A concentration quotient of 1.1M ^?1 was obtained for the formation of the Ag⁺NO ₃ ^? ion pair when C<4M. The complex appears to have point group C_s(σ_V) with Ag⁺ in a “roll-on” position. The Ag⁺ ion is solvated by four molecules of CH₃CN; nitrate ion replaces three of these when bound to Ag⁺. When C>4M, multiple ion aggregates form in the solution. A low-frequency 110 cm^?1 line is ascribed to librational motions of NO ₃ ^? , probably bound to Ag⁺.     

Optical Activity of Metal Nanoclusters Deposited on Regular and Doped Oxide Supports from First-Principles Simulations

We report a computational study and analysis of the optical absorption processes of Ag₂₀ and Au₂₀ clusters deposited on the magnesium oxide (100) facet, both regular and including point defects. Ag₂₀ and Au₂₀ are taken as models of metal nanoparticles and their plasmonic response, MgO as a model of a simple oxide support. We consider oxide defects both on the oxygen anion framework (i.e., a neutral oxygen vacancy) and in the magnesium cation framework (i.e., replacing Mg⁺⁺ with a transition metal: Cu⁺⁺ or Co⁺⁺). We relax the clusters’ geometries via Density-Functional Theory (DFT) and calculate the photo-absorption spectra via Time-Dependent DFT (TDDFT) simulations on the relaxed geometries. We find that the substrate/cluster interaction induces a broadening and a red-shift of the excited states of the clusters, phenomena that are enhanced by the presence of an oxygen vacancy and its localized excitations. The presence of a transition-metal dopant does not qualitatively affect the spectral profile. However, when it lies next to an oxygen vacancy for Ag₂₀, it can strongly enhance the component of the cluster excitations perpendicular to the surface, thus favoring charge injection.     

Structural investigation of (CuI)0.45–(Ag2WO4)0.55 solid electrolyte using X-ray photoelectron and laser Raman spectroscopies

X-ray photoelectron spectroscopy (XPS) and laser Raman scattering (LRS) techniques have been employed to investigate the structure of amorphous (CuI)_0.45–(Ag₂WO₄)_0.55 solid electrolyte sample. XPS results reveal the presence of both Cu⁺ and Cu²⁺ ions whereas tungsten is found to exist only in the oxidation state of +6. The deconvolution of the O 1s spectrum into non-bridging and bridging oxygen atoms in conjunction with the laser Raman analysis tend to show that the amorphous (CuI)_0.45–(Ag₂WO₄)_0.55 solid electrolyte sample is composed mostly of octahedral WO₆ units that probably form [W₄O₁₆]⁸⁻ tetramer clusters, the existence of which is unique in the case of oxyhalide glasses.     

Etude spectroscopique de derives mercuriques d'amides-thiols: I. Spectres de vibration et structure des thiol-2 N-méthylacétamide,thiol-3 N-méthylpropanamide et N-(thiol-2 éthyle) acétamide

Raman and infrared spectra of CH₃NHCOCH₂SH, CH₃NHCO(CH₂)₂SH and CH₃CONH(CH₂)₂SH have been recorded between 3800 and 200 cm^?1. Some structural information is obtained from their analysis: for pure liquids or solids, molecules form linear chains with NH ? OC hydrogen bonds, the SH group being probably bound to the oxygen of an adjacent molecule. For CCl₄ solutions, an intramolecular hydrogen bond NH ? S is observed for the first compound only, corresponding to the formation of a five-membered ring.     

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.     

Atomic‐Level Alloying and De‐alloying in Doped Gold Nanoparticles

Atomically precise alloying and de‐alloying processes for the formation of Ag–Au and Cu–Au nanoparticles of 25‐metal‐atom composition (referred to as Ag_xAu_25?x(SR)₁₈ and Cu_xAu_25?x(SR)₁₈, in which R=CH₂CH₂Ph) are reported. The identities of the particles were determined by matrix‐assisted laser desorption ionization mass spectroscopy (MALDI‐MS). Their structures were probed by fragmentation analysis in MALDI‐MS and comparison with the icosahedral structure of the homogold Au₂₅(SR)₁₈ nanoparticles (an icosahedral Au₁₃ core protected by a shell of Au₁₂(SR)₁₈). The Cu and Ag atoms were found to preferentially occupy the 13‐atom icosahedral sites, instead of the exterior shell. The number of Ag atoms in Ag_xAu_25?x(SR)₁₈ (x=0–8) was dependent on the molar ratio of Ag^I/Au^III precursors in the synthesis, whereas the number of Cu atoms in Cu_xAu_25?x(SR)₁₈ (x=0–4) was independent of the molar ratio of Cu^II/Au^III precursors applied. Interestingly, the Cu_xAu_25?x(SR)₁₈ nanoparticles show a spontaneous de‐alloying process over time, and the initially formed Cu_xAu_25?x(SR)₁₈ nanoparticles were converted to pure Au₂₅(SR)₁₈. This de‐alloying process was not observed in the case of alloyed Ag_xAu_25?x(SR)₁₈ nanoparticles. This contrast can be attributed to the stability difference between Cu_xAu_25?x(SR)₁₈ and Ag_xAu_25?x(SR)₁₈ nanoparticles. These alloyed nanoparticles are promising candidates for applications such as catalysis.     

Evolution from superatomic Au24Ag20 monomers into molecular-like Au43Ag38 dimeric nanoclusters

Hierarchical assembly of nanoparticles has been attracting wide interest, as advanced functionalities can be achieved. However, the ability to manipulate structural evolution of artificial nanoparticles into assemblies with atomic precision has been largely unsuccessful. Here we report the evolution from monomeric Au₂₄Au₂₀ into dimeric Au₄₃Ag₃₈ nanoclusters: Au₄₃Ag₃₈ inherits the kernel frameworks from parent Au₂₄Ag₂₀ but exhibits distinct surface motifs; Au₂₄Ag₂₀ is racemic, while Au₄₃Ag₃₈ is mesomeric. Importantly, the evolution from monomers to dimers opens up exciting opportunities exploring currently unknown properties of monomeric and dimeric alloy nanoclusters. The Au₂₄Ag₂₀ clusters show superatomic electronic configurations, while Au₄₃Ag₃₈ clusters have molecular-like characteristics. Furthermore, monomeric Au₂₄Ag₂₀ catalysts readily outperform dimeric Au₄₃Ag₃₈ catalysts in the catalytic reduction of CO₂.

The work shows the evolution from monomeric Au₂₄Au₂₀ into dimeric Au₄₃Ag₃₈ nanoclusters and provides exciting opportunities for atomic manufacturing on metal nanoclusters to construct structures and functionality.     

Aggregation-induced phosphorescence sensitization in two heptanuclear and decanuclear gold–silver sandwich clusters

The strategy of aggregation-induced emission enhancement (AIEE) has been proven to be efficient in wide areas and has recently been adopted in the field of metal nanoclusters. However, the relationship between atomically precise clusters and AIEE is still unclear. Herein, we have successfully obtained two few-atom heterometallic gold–silver hepta-/decanuclear clusters, denoted Au₆Ag and Au₉Ag, and determined their structures by X-ray diffraction and mass spectrometry. The nature of the Au^I⋯Ag^I interactions thereof is demonstrated through energy decomposition analysis to be far-beyond typical closed-shell metal–metal interaction dominated by dispersion interaction. Furthermore, a positive correlation has been established between the particle size of the nanoaggregates and the photoluminescence quantum yield for Au₆Ag, manifesting AIEE control upon varying the stoichiometric ratio of Au : Ag in atomically-precise clusters.

The strategy of aggregation-induced emission enhancement (AIEE) has been proven to be efficient in wide areas and has recently been adopted in the field of metal nanoclusters.     

Density functional study of structural and electronic properties of maximum‐spin n+1Aun−1Ag clusters

The structures and relative stabilities of high‐spin ⁿ⁺¹Au_n?1Ag and ⁿAu_n?1Ag⁺ (n = 2–8) clusters have been studied with density functional calculation. We predicted the existence of a number of previously unknown isomers. Our results revealed that all structures of high‐spin neutral or cationic Au_n?1Ag clusters can be understood as a substitution of an Au atom by an Ag atom in the high‐spin neutral or cationic Au_n clusters. The properties of mixed gold–silver clusters are strongly sized and structural dependence. The high‐spin bimetallic clusters tend to be holding three‐dimensional geometry rather than planar form represented in their low‐spin situations. Silver atom prefers to occupy those peripheral positions until to n = 8 for high‐spin clusters, which is different from its position occupied by light atom in the low‐spin situations. Our theoretical calculations indicated that in various high‐spin Au_n?1Ag neutral and cationic species, ⁵Au₃Ag, ³AuAg and ⁵Au₄Ag⁺ hold high stability, which can be explained by valence bond theory. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009