The chemistry of gold as an anion

Due to relativistic and classical shell structure effects, the 6s orbital of gold is significantly contracted and energetically stabilized. This is reflected by a strikingly high electron affinity, and a distinct tendency to adopt negatively polarized valence states. This tutorial review focuses on the chemistry of gold as an anion, displaying the integral ionic charge number of 1-. Two synthetic approaches to compounds containing monoatomic gold anions have become available: (1) reacting elemental gold with molten caesium and an oxide, e.g. Cs(2)O; (2) metathesis reactions involving Au(-) dissolved in liquid ammonia. Both procedures have proven to be rather versatile. Aurides synthesized along these routes are surveyed, in particular with respect to their structures and bonding properties.     

Luminescent gold(I) complexes for chemosensing

With the rich spectroscopic and luminescence properties associated with aurophilic Au?Au interactions, gold(I) complexes have provided an excellent platform for the design of luminescent chemosensors. This review concentrates on our recent exploration of luminescent gold(I) complexes in host–guest chemistry. Through the judicious design and choice of the functional receptor groups, specific chemosensors for cations and/or anions have been obtained. Utilization of sensing mechanisms based on the on–off switching of Au?Au interactions and photoinduced electron transfer (PET) has been successfully demonstrated. The two-coordinate nature of gold(I) complexes has also been utilized for the design of ditopic receptors through connecting both cation- and anion-binding sites within a single molecule.     

Synthesis,Optical Properties,and Sensing Applications of Gold Nanodots

In this Personal Account, we briefly address our journey in developing photoluminescent nanomaterials for sensing purposes, with a focus on gold nanodots (Au NDs). Their synthetic strategies, optical properties, and sensing applications are emphasized. The Au NDs can be simply prepared from the etching of small‐sized Au nanoparticles (<3 nm in diameter) by thiol compounds such as 11‐mercaptoundecanoic acid under alkaline conditions. This simple approach allows the preparation of various functional Au NDs by choosing different thiol compounds as etching agents. Since the optical properties of Au NDs are highly dependent on the core and shell of each Au ND, the selection of etching reagents is important. Over the years we have developed various sensing systems using Au NDs for the detection of metal ions, anions, and proteins, based on analyte‐induced photoluminescence quenching/enhancement of Au NDs as a result of changes in their oxidation state, shell composition, and structure.     

Excimer and Exciplex Formation in Gold(I) Complexes Preconditioned by Aurophilic Interactions

Excimers and exciplexes are defined as assemblies of atoms or molecules A / A ′ where interatomic/intermolecular bonding appears only in excited states such as [ A ₂]* (for excimers) and [ AA ′]* (for exciplexes). Their formation has become widely known because of their role in gas‐phase laser technologies, but their significance in general chemistry terms has been given little attention. Recent investigations in gold chemistry have opened up a new field of excimer and exciplex chemistry that relies largely on the preorganization of gold(I) compounds (electronic configuration Au^I(5d¹⁰)) through aurophilic contacts. In the corresponding excimers, a new type of Au???Au bonding arises, with bond energies and lengths approaching those of ground‐state Au?Au bonds between metal atoms in the Au⁰(5d¹⁰6s¹) and Au^II(5d⁹) configurations. Excimer formation gives rise to a broad range of photophysical effects, for which some of the relaxation dynamics have recently been clarified. Excimers have also been shown to play an important role in photoredox binuclear gold catalysis.     

Electrocatalytic and photocatalytic applications of atomically precise gold-based nanoclusters

With advances in cluster chemistry, atomically precise gold nanoclusters(NCs) with well-defined composition and tunable structure provide an exciting opportunity to uncover the specific roles of the geometrical and electronic structures as well as the capped ligands in overall catalytic performances. The Au NCs possess quantum energy levels and unique optical properties,which have exhibited unexpected photocatalytic and electrocatalytic activities. In this review, we first highlight the electrocatalytic applications of Au NCs, including hydrogen evolution reaction, oxygen reduction reaction, CO_2 reduction and catalytic oxidation reactions, and then present Au NCs-driven photocatalytic applications such as selective organic reactions, decomposition of pollutants and energy conversion reactions. Finally, we conclude this review with a brief perspective on the catalytic field of Au NCs.     

Mechanism of trivalent gold reduction and reactivity of transient divalent and monovalent gold ions studied by gamma and pulse radiolysis

The detailed kinetics of the multistep mechanism of the Au(III) ion reduction into gold clusters have been investigated by radiation chemistry methods in 2-propanol. In particular, a discussion on the steady state radiolysis dose-dependence of the yields concludes to a comproportionation reaction of nascent gold atoms Au(0) with excess Au(III) ions into Au(II) and Au(I). This reaction should be achieved through Au(III) consumption before the coalescence of atoms Au(0) into gold clusters may occur. Then gold clusters catalyze the reduction of Au(I) by 2-propanol. It was also found that a long-lived Au(II) dimer, (Au(II))(2), was transiently formed according to the quantitative analysis of time-resolved absorbance signals obtained by pulse radiolysis. Then the disproportionation of Au(II) is intramolecular in the dimer instead of intermolecular, as usually reported. The yields, reaction rate constants, time-resolved spectra, and molar extinction coefficients are reported for the successive one-electron reduction steps, involving especially the transient species, such as Au(II), (Au(II))(2), and Au(I). The processes are discussed in comparison with other solvents and other metal ions.     

Au42: an alternative icosahedral golden fullerene cage

We present a new icosahedral gold fullerene, Au42, based on density functional theory calculations. The Au42 fullerene has a nanoscale hollow space that can hold up to 13 Au atoms. The Au42 fullerene also has a larger HOMO-LUMO gap compared to the compact-filling geometries. However, unlike the known gold fullerene Au32, the Au42 fullerene does not satisfy the 2(N + 1)2 aromatic rule and has a positive NICS value at the center of the cage. These two nanometer-sized gold fullerenes can be used as golden cages to accommodate other atoms or molecules for the purpose of studying fundamental chemistry because of their apparently dissimilar chemical characteristics, or they can be used as structural motifs to build highly stable core-shell nanoclusters or novel cluster-assembled materials.     

Electron density fitting for the Coulomb problem in relativistic density-functional theory

A density fitting approach for the Coulomb matrix representation within the four-component formulation of relativistic density-functional theory is presented. Our implementation, which uses G-spinor basis sets, shares all the advantages of those found in nonrelativistic quantum chemistry. We show that very accurate Coulomb energies may be obtained using a modest number of scalar auxiliary basis functions for molecules containing heavy atoms. The efficiency of this new implementation is demonstrated in a detailed study of the spectroscopic properties of the gold dimer, and its scaling behavior has been tested by calculations of some closed-shell gold clusters (Au2, Au3+, Au4, Au5+). The algorithm is found to scale as O(N3), just as it does in the nonrelativistic case, and represents a dramatic improvement in efficiency over the conventional approach in the calculation of the Coulomb matrix, with computation times that are reduced to less than 3% for Au2 and up to 1% in the case of Au5+.     

Experimental and DFT studies of gold nanoparticles supported on MgO(111) nano-sheets and their catalytic activity

A wet chemical preparation of MgO with the (111) facet as the primary surface has recently been reported and with alternating layers of oxygen anions and magnesium cations, this material shows unique chemical and physical properties. The potential to utilize the MgO(111) surface for the immobilization of metal particles is intriguing because the surface itself offers a very different environment for the metal particle with an all oxygen interface, as opposed to the typical (100) facet that possesses alternating oxygen anion and magnesium cation sites on the surface. Gold nanoparticles have demonstrated a broad range of interesting catalytic properties, but are often susceptible to aggregation at high temperatures and are very sensitive to substrate effects. Here, we investigate gold-supported on MgO(111) nanosheets as a catalyst system for the aerobic oxidation of benzyl alcohol. Gold nanoparticles deposited on MgO(111) show an increased level of activity in the solvent-free benzyl alcohol aerobic oxidation as compared to gold nanoparticles deposited on a typical MgO aerogel. TEM studies reveal that the gold nanoparticles have a hemispherical shape while sitting on the main surface of MgO(111) nanosheets, with a large Au-MgO interface. Given that the gold nanoparticles deposited on the two types of MgO have similar size, and that the two types of unmodified MgO show almost the same activities in the blank reaction, we infer that the high activity of Au/MgO(111) is due to the properties of the (111) support and/or those of the gold-support interface. To understand the binding of Au on low-index MgO surfaces and the charge distribution at the surface of the support, we have performed density functional theory (DFT) calculations on all low-index MgO substrates (with and without gold), using a model Au(10) cluster. Due to similar lattice constants of Au(111) and MgO(111) planes, the Au cluster retains its structural integrity and binds strongly on MgO(111) with either oxygen or magnesium termination. Furthermore, we have found that for the (001) and (110) substrates the charges of the ions in the top surface layer have similar values as in bulk MgO, but that on (111) surfaces these charges are significantly different. This difference in surface charge determines the direction of the electronic transfer upon adsorption of gold, such transfer occurring so as to restore the bulk MgO charge values. Using the results from theoretical calculations, we provide an explanation of our observations of increased catalytic activity in the case of the Au/MgO(111) system.     

Structure of incommensurate gold sulfide monolayer on Au(111)

We develop an atomic-scale model for an ordered incommensurate gold sulfide (AuS) adlayer which has previously been demonstrated to exist on the Au(111) surface, following sulfur deposition and annealing to 450 K. Our model reproduces experimental scanning tunneling microscopy images. Using state-of-the-art Wannier-function-based techniques, we analyze the nature of bonding in this structure and provide an interpretation of the unusual stoichiometry of the gold sulfide layer. The proposed structure and its chemistry have implications for related S-Au interfaces, as in those involved in self-assembled monolayers of thiols on Au substrates.     

Saturated adsorption of CO and coadsorption of CO and O2 on AuN- (N=2-7) clusters

A first-principles quantum chemistry method, based on the Kohn-Sham density-functional theory, is used to investigate the adsorption of CO and O2 on small gas-phase gold cluster anions. The saturated adsorption of carbon monoxide on gold cluster anions AuN- (N=2-7) is discussed. The adsorption ability of CO reduces with the increase of the number of CO molecules bound to gold cluster anions, resulting in saturated adsorption at a certain amount of absorbed CO molecules, which is determined by geometric and electronic properties of gold clusters cooperatively. The effect of CO preadsorption on the electronic properties of gold cluster anions depends on the cluster size and the number of adsorbed CO, and the vertical detachment energies of CO-adsorbed gold cluster anions show a few changes with respect to corresponding pure gold cluster anions. The results indicate that the impinging adsorption of CO molecules may lead to geometry structure transformation on Au3- cluster. For the coadsorption of CO and O2 on Au2-, Au3- isomers, Au4-, and Au6-, we describe the cooperative adsorption between CO and O2, and find that the O2 dissociation is difficult on gas-phase gold cluster anions even with the preadsorption of CO.     

Gold‐Catalyzed Cascade Reactions for Synthesis of Carbo‐ and Heterocycles: Selectivity and Diversity

This account describes our recent efforts devoted to gold chemistry since 2009. Based on furyl–Au 1,3‐dipole analogues and related gold carbene intermediates, a rich variety of gold‐catalyzed cascade reactions have been developed, which provide facile access to a diverse range of novel carbo‐ and heterocycles. In these reactions, the selectivity can be well controlled by the catalyst (ligand and metal), substrate or reagent. In addition, we have also developed the corresponding enantioselective variants, which are guided by bis(phosphinegold) complexes derived from axially chiral scaffolds and asymmetric gold/chiral Brønsted acid relay catalysis.     

Gold Nanoparticles Supported on Mesoporous Titania Thin Films with High Loading as a CO Oxidation Catalyst

In the present work, 2.4 nm gold nanoparticles (Au NPs) are uniformly dispersed on mesoporous titania thin films which are structurally tuned by controlling the calcination temperature. The gold content of the catalyst is as high as 27.8 wt %. To our knowledge, such a high loading of Au NPs with good dispersity has not been reported until now. Furthermore, the reaction rate of the gold particles is enhanced by one order of magnitude when supported on mesoporous titania compared to non‐porous titania. This significant improvement can be explained by an increase in the diffusivity of the substrate due to the presence of mesopores, the resistance to agglomeration, and improved oxygen activation.     

Structural characterization, solution studies, and DFT calculations on a series of binuclear gold(III) oxo complexes: relationships to biological properties

A series of structurally related oxo-bridged binuclear gold(III) compounds, [Au2(mu-O)2(N;N)2](PF6)2, where N;N is 2,2'-bipyridine or a substituted 2,2'-bipyridine, have recently been shown to exhibit appreciable stability under physiological-like conditions and to manifest important antiproliferative effects toward selected human tumor cell lines (J. Med. Chem. 2006, 49, 5524). The crystal structures of four members of this series, namely, [Au2(mu-O)2(bipy)2](PF6)2, cis-[Au2(mu-O)2(6-Mebipy)2](PF6)2, trans-[Au2(mu-O)2(6-oXylbipy)2](PF6)2, and [Au2(mu-O)2(6,6'-Me2bipy)2](PF6)2, have been solved here and the respective structural parameters comparatively analyzed. Remarkably, all of the compounds contain a common structural motif consisting of a Au2O2 "diamond core" linked to two bipyridine ligands in a roughly planar arrangement. Interestingly, introduction of different kinds of alkyl or aryl substituents on the 6 (and 6') position(s) of the bipyridine ligand leads to small structural changes that nonetheless greatly affect the reactivity of the metal centers. The chemical behavior of these compounds in solution has been studied in detail, focusing in particular on the electrochemical properties. Some initial correlations among the structural parameters, the chemical behavior in solution, and the known cytotoxic effects of these compounds are proposed. Notably, we have found that the 6,6'-dimethyl-2,2'-bipyridine derivative, which showed the largest structural deviations with respect to the model compound [Au2(mu-O)2(bipy)2](PF6)2, also had the highest oxidizing power, the least thermal stability, and the greatest cytotoxic activity. The positive correlation that exists between the oxidizing power and the antiproliferative effects seems to be of particular interest. Moreover, the electronic structures of these compounds were extensively analyzed using DFT methods, and the effects of the various substituents on reactivity were predicted; overall, very good agreement between theoretical expectations and experimental data was achieved. In turn, theoretical predictions offer interesting hints for the design of new, more active binuclear gold(III) compounds.     

Activation of gold on titania: adsorption and reaction of SO(2) on Au/TiO(2)(110)

Synchrotron-based high-resolution photoemission and first-principles density-functional slab calculations were used to study the interaction of gold with titania and the chemistry of SO(2) on Au/TiO(2)(110) surfaces. The deposition of Au nanoparticles on TiO(2)(110) produces a system with an extraordinary ability to adsorb and dissociate SO(2). In this respect, Au/TiO(2) is much more chemically active than metallic gold or stoichiometric titania. On Au(111) and rough polycrystalline surfaces of gold, SO(2) bonds weakly and desorbs intact at temperatures below 200 K. For the adsorption of SO(2) on TiO(2)(110) at 300 K, SO(4) is the only product (SO(2) + O(oxide) --> SO(4,ads)). In contrast, Au/TiO(2)(110) surfaces (theta;(Au) < or = 0.5 ML) fully dissociate the SO(2) molecule under identical reaction conditions. Interactions with titania electronically perturb gold, making it more chemically active. Furthermore, our experimental and theoretical results show quite clearly that not only gold is perturbed when gold and titania interact. The adsorbed gold, on its part, enhances the reactivity of titania by facilitating the migration of O vacancies from the bulk to the surface of the oxide. In general, the complex coupling of these phenomena must be taken into consideration when trying to explain the unusual chemical and catalytic activity of Au/TiO(2). In many situations, the oxide support can be much more than a simple spectator.     

Fabrication of Translucid Gold-Nanocellulose Electrodes and their Potential Application as Hydrogen Peroxide Sensor

In this work, we describe the fabrication of a transparent gold electrode based on nanocellulose. The electrode was prepared via electron beam evaporation of gold onto nanocellulose films previously spread over a glass slip. Electrodes with different thickness of Au was fabricated, and the material's optical, morphological and electrical properties were assessed. Finally, as a proof of concept, a possible application of this electrode in hydrogen peroxide sensing was performed. The results show that a thin layer of gold on a nanocellulose translucid film allows obtaining a conductive transparent surface that could be used to design a transparent electrode.     

Simple Synthetic Routes to N-Heterocyclic Carbene Gold(I)–Aryl Complexes: Expanded Scope and Reactivity

The discovery of sustainable and scalable synthetic protocols leading to gold–aryl compounds bearing N-heterocyclic carbene (NHC) ligands sparked an investigation of their reactivity and potential utility as organometallic synthons. The use of a mild base and green solvents provide access to these compounds, starting from widely available boronic acids and various [Au(NHC)Cl] complexes, with reactions taking place under air, at room temperature and leading to high yields with unprecedented ease. One compound, (N,N′-bis[2,6-(di-isopropyl)phenyl]imidazol-2-ylidene)(4-methoxyphenyl)gold, ([Au(IPr)(4-MeOC₆H₄)]), was synthesized on a multigram scale and used to gauge the reactivity of this class of compounds towards C−H/N−H bonds and with various acids, revealing simple pathways to gold–based species that possess attractive properties as materials, reagents and/or catalysts.     

Effects of the Au(I)–Au(I) closed‐shell attraction on the electronic and phosphorescent properties in a series of coordination compounds: A theoretical study

The Au(I)–Au(I) closed‐shell or aurophilic attraction has been the subject of interest in the experimental and theoretical chemistry fields, due to the intriguing properties associated to it. The presence of phosphorescence in “aurophilic” compounds has been addressed to a wide range of applications, but it has not yet been fully understood. A theoretical study on the electronic and phosphorescent properties of the following series of dinuclear gold complexes has been performed: [Au₂(dmpm) (i‐mnt)] ( 1 ), [Au₂(μ‐Me‐TU) (μ‐dppm)] ( 2 ), and [Au₂(μ‐G)(μ‐dmpe)] ( 3 ). Full geometry optimizations at the second‐order Møller–Plesset perturbation theory (MP2) were carried out for each of the species. These calculations made evident that, at the ground‐state geometry, the Au(I) cations allocated at the center of the ring show a short Au–Au distance below the sum of the van der Waals radii, at the range of the aurophilic attraction. An intermolecular Au(I)–Au(I) closed‐shell attraction for a pair of the systems under study is found. This attraction is comparable to that of the hydrogen bonds. The phosphorescent properties experimentally observed for this series were also characterized through ab initio techniques. The obtained results allow to fit reasonably the excitation energies with the experimental data and to identify a correlation between the strength of the Au(I)–Au(I) interaction and the phosphorescent behavior. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

电子废弃物中金元素的绿色溶解与提取

电子废弃物中含有Au、Pt、Pd、Ag等多种贵重金属,其处理处置的无害化、资源化成为目前一项重要课题。本文通过使用安全的试剂来溶解金,从而达到从含金废弃物中回收金的目的,说明利用配体与金形成配合物从而有效降低溶金电极电势的化学原理。普及科学原理,树立科学理念。介绍电子废弃物处置的常识,普及绿色化学的观念,避免新的污染与危险,树立环境保护的观念。     

Gold complexes with dithiothiophene ligands: a metal based on a neutral molecule

The gold complexes n-Bu4N[Au(alpha-tpdt)2] (5), n-Bu4N[Au(dtpdt)2] (4) and n-Bu4N[Au(tpdt)2] (6) based on new dithiothiophene ligands (alpha-tpdt= 2,3-thiophenedithiolate, dtpdt=2,3-dihydro-5,6-thiophenedithiolate and tpdt = 3,4-thiophenedithiolate) have been prepared and characterised. These gold(III) complexes are diamagnetic, but they can be oxidised with iodine to the paramagnetic compounds [Au(alpha-tpdt)2] (8), [Au(dtpdt)2] (7) and n-Bu4N[[Au(tpdt)2]n-2] (9), which were isolated as fine powders and which exhibit paramagnetic susceptibilities that are almost temperature independent with room temperature values of 2.5 x 10(-4), 2.0 x 10(-4) and 5 x 10(-4) emu x mol(-1), respectively. Interestingly, the neutral complex [Au(alpha-tpdt)2] (8) as a polycrystalline sample displays the properties of a metallic system with a room temperature electrical conductivity of 6 S x cm(-1) and a thermoelectric power of 5.5 microVK(-1); this is the first time that this metallic property has been observed in a molecular system based on a neutral species.