Au Oxidation Research Articles

Electrooxidation of methanol and ethylene glycol on gold and on gold modified with an electrodeposited polyNiTSPc film

The electrooxidation of methanol and ethylene glycol on Au and on polynickeltetrasulphophthalocyanine-modified gold (polyNiTSPc/Au/Q) electrodes in a pH 11 carbonate/hydrogen carbonate buffer electrolyte was studied by cyclic voltammetry (CV) and with an electrochemical quartz crystal microbalance (EQCM). Au shows negligible activity for methanol oxidation, in agreement with the fact that methanol does not adsorb on Au, since it does not affect the potential at which the mass increase due to Au oxidation starts. On the contrary, ethylene glycol (EG) is electrooxidized on Au at a significant rate, probably because it adsorbs rather strongly on Au, as evidenced by the positive shift by 0.35 V of the mass increase attending Au monolayer oxidation. The polyNiTSPc-modified Au electrodes are hydrophobic, as inferred from the disappearance of the large mass decrease in the double-layer region typical of the bare Au electrode, a decrease which is due to the desorption of the water molecules adsorbed at the negative potential limit. On the polyNiTSPc/Au/Q electrodes the current at the positive potential limit (at which only Ni(III) exists) of methanol oxidation, and the peak current of EG oxidation (at a potential at which only Ni(II) exists), show a Langmuir dependence on the concentration, which indicates that in both cases the reactive species are adsorbed, and that their oxidation rate is much lower than the adsorption rate. As is well known, the oxidation of Ni(II) to Ni(III) in the polyNiTSPc film is accompanied by a large mass decrease, due mostly to the expulsion of water from the film by the hydrophobic Ni(III). This mass decrease is independent of the scan rate, but in the presence of methanol or ethylene glycol it increases with increasing scan rate, which indicates that the oxidation of the alcohols involves a chemical reaction of the alcohols with Ni(III) ions, the extent of which decreases with increasing rate. Consequently, the amount of the hydrophobic Ni(III) will increase, and so will the mass loss. The mass decrease of Ni(II) oxidation decreases with increasing concentration of methanol or ethylene glycol, which again shows that there is a chemical reaction between the alcohols and Ni(III) ions, since the concentration of the latter would decrease with increasing alcohol concentration.

Nanostructured Porous Gold for Methanol Electro-Oxidation

Dealloying single phase alloys is known to generate a type of nanostructured porous metals with intriguing properties. In this study, nanoporous gold (NPG) made by dealloying Au−Ag is investigated as a novel electrode material for methanol electro-oxidation. Compared to bulk Au electrode, oxidation and subsequent reduction of NPG occur at significantly negative potentials in both acid and alkaline solutions. NPG shows great catalytic activity for methanol electro-oxidation, but the structure quickly coarsens upon long time potential cycling. Interestingly, after surface modification with only a tiny amount of platinum, NPG exhibits greatly enhanced electrocatalytic activity toward methanol oxidation in the alkaline solutions, which is exemplified by a broad and high anodic peak during the positive scan and two secondary oxidation peaks in the subsequent reverse scan. At the same time, SEM observation and long-time potential cycling both prove that Pt−NPG has much enhanced structure stability as compared w...

Oxidation of Au on vicinal W(110): Role of step edges and facets

The electronic and chemical properties of Au on stepped surface oxides are of great fundamental and practical interest. Vicinal W(110) substrates have been used as templates for deposition and oxidation of submonolayer amounts of Au. Crystal surfaces of flat W(110), W(145) with the densest step edges, and W(331) and W(551) with open step edges were employed as model systems. By photoemission from the $4f$ core levels of Au and W, the most dramatic changes to the ionic state of the Au, resulting in complete oxidation, were observed on preoxidized W(331) and W(551) after annealing at $900\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. By scanning tunneling microscopy, it was found that chemisorption of oxygen causes nanofaceting of the vicinal W(110) surfaces. The impact of the facets on the surface chemistry revealed by the experiment is discussed. The dimensions and periodicity of the facets were found to be a principal factor in Au oxidation.

Potential of Chilopsis Linearis for Gold Phytomining: Using Xas to Determine Gold Reduction and Nanoparticle Formation Within Plant Tissues

This study reports on the capability of the desert plant Chilopsis linearis (Cav.) Sweet (desert willow) to uptake gold (Au) from gold-enriched media at different plant-growth stages. Plants were exposed to 20, 40, 80, 160, and 320 mg Au L−1 in agar-based growing media for 13, 18, 23, and 35 d. The Au content and oxidation state of Au in the plants were determined using an inductively coupled plasma/optical emission spectrometer (ICP/OES) and X-ray absorption spectroscopy (XAS), respectively. Gold concentrations ranging from 20 to 80 mg Au L−1 did not significantly affect Chilopsis linearis plant growth. The concentration of gold in the plants increased as the age of the plant increased. The Au concentrations in leaves for the 20, 40, 80, and 160 mg Au L−1 treatments were 32, 60, 62, and 179 mg Au kg−1 dry weight mass, respectively, demonstrating the gold uptake capability of desert willow. The XAS data indicated that desert willow produced gold nanoparticles within plant tissues. Plants exposed to 160 mg Au L−1 formed nanoparticles that averaged approximately 8, 35, and 18 Å in root, stem, and leaves, respectively. It was observed that the average size of the Au nanoparticles formed by the plants is related to the total Au concentration in tissues and their location in the plant

Electrochemical characterization of the underpotential deposition of tellurium on Au electrode

Electrochemical characterization of the underpotential deposition (UPD) of tellurium on Au substrate has been performed in this paper. The mechanism of Te deposition and its voltammetry dependence on the Te ion concentration were studied, and it suggests that variations in the metal ion concentration may affect the UPD process kinetics. The effect of tellurium adsorbates on UPD behavior of Te has also been investigated. The results show that the tellurium adsorbates could be irreversibly adsorbed upon the Au substrate surface under the open-circuit conditions. Subsequent removal of the Te adsorbates was also proved to be very difficult within the Au double-layer region, and a standard electrochemical cleaning procedure is necessary to remove the Te adsorbates completely. When the potential was cycled into the Au oxidation region, a substantial loss of Te adsobates was observed, which occurs simultaneously with the Au oxidation features. Scan rate dependent cyclic voltammetry experiments reveal that the peak current in the Te UPD peak is not a linear function of the scan rate, ν, but of a 2/3 power of the scan rate, ν 2/3. It is in good consistent with a two-dimension nucleation and growth mechanism.

Rich Coordination Chemistry of Au Adatoms in Gold Sulfide Monolayer on Au(111)

The rich chemistry of Au nanoparticles and ions has attracted tremendous interest, in part because the surfaces of bulk Au have traditionally been considered to be chemically inert. On the other hand, large-scale mass transport and the formation of vacancy islands have been observed on the Au(111) surface following the deposition of adsorbates, such as sulfur and thiols, that can interact strongly with the Au surface. In this work, we revisit the structure and chemistry of an ordered incommensurate AuS adlayer that forms on Au(111) following the deposition of sulfur and annealing to 450 K. A structural model of this AuS surface phase has not yet been determined experimentally due to the complexity of the system. Here, we use state-of-the-art density functional theory to develop an atomic-scale model that is consistent with the previously reported Au-S stoichiometry. In particular, we introduce theoretical techniques to take into account the charge transfer in an incommensurate system. Our model reproduces convincingly STM images and is remarkably robust. Bonding analysis based on Wannier functions shows that the model exhibits rich coordination chemistry corresponding to different Au oxidation states. The extraordinary stability and rich chemistry of this structure have implications for related S-Au interfaces and previously reported surface features of this system.

Enhancement of O2 Dissociation on Au(111) by Adsorbed Oxygen: Implications for Oxidation Catalysis

We show that the dissociation probability of O2 on the reconstructed, Au111-herringbone surface is dramatically increased by the presence of some atomic oxygen on the surface. Specifically, at 400 K the dissociation probability of O2 on oxygen precovered Au111 is on the order of 10(-3), whereas there is no measurable dissociation on clean Au111, establishing an upper bound for the dissociation probability of 10(-6). Atomic oxygen was deposited on the clean reconstructed Au111-herringbone surface using electron bombardment of condensed NO2 at 100 K. The dissociation probability for dioxygen was measured by exposing the surface to 18O2. Temperature programmed desorption (TPD) was used to quantify the amount of oxygen dissociation and to study the stability of the oxygen in all cases. Oxygen desorbs as O2 in a peak centered at 550 K with pseudo-first-order kinetics; i.e., the desorption peak does not shift with coverage. Our interpretation is that the coverage dependence of the activation energy for dissociation (deltaE(dis)) and/or preexponential factor (nu(d)) may be responsible for the unusual desorption kinetics, implying a possible energy barrier for O2 dissociation on Au111. These results are discussed in the context of Au oxidation chemistry and the relationship to supported Au nanoparticles.

Kinetic Parameters and Mechanism of Gold Electrooxidation in Thiocarbamide Solutions

Kinetics and mechanism of gold electrooxidation in sulfuric acid solutions of thiocarbamide (TCA) are studied by measuring voltammograms (VA) of gold and glassy carbon (GC) electrodes. In a potential (E) range from −0.2 to 1.2 V (SCE), VA of a gold electrode demonstrate three peaks. The first and the second peaks correspond to gold electrooxidation to [AuTCAads] + and [Au(TCAads)3]3+ ions at E of 0.152 and 0.554 V, while the third one corresponds to TCA electrooxidation. The electrooxidation of TCA on GC electrodes is characterized by two VA peaks at 0.983 and 1.437 V. The first peak corresponds to the formation of formamidine disulfide (FADS) (ka1 = 6.40 × 10−4 cm/s), while the second peak corresponds to TCA oxidation to sulfides and hydrosulfides (ka2 = 7.78 × 10−5 cm/s). The composition of adsorption layers formed at the Au electrode is analyzed by Auger spectroscopy. The introduction of sodium sulfide into TCA solutions eliminates the formation of adsorption layers and accelerates Au oxidation in such solutions. The rate constants of gold electrooxidation ka = 6.31 × 10−3 cm/s and Au(I) electroreduction kc = 5.46 × 10−4 cm/s in TCA solutions are estimated. Kinetic parameters (charge transfer coefficients, reactions orders in carbamide) are determined and the mechanisms of Au and TCA oxidation in sulfuric acid solutions are proposed.

Investigation of Alumina-Supported Au Catalyst for CO Oxidation by Isotopic Transient Analysis and X-ray Absorption Spectroscopy

Alumina-supported Au particles (1.16 wt %) were prepared by a deposition-precipitation method involving a HAuCl4 precursor. X-ray absorption spectroscopy at the Au L(III) edge was used to monitor the evolution of the Au oxidation state and atomic structure during pretreatment in He up to 623 K. Although the as-prepared material had Au present in a +3 oxidation state, thermal treatment at 623 K facilitated autoreduction of Au cations to metal particles. Analysis of the EXAFS revealed a coordination number (Au-Au) of 7.2, which is consistent with spherical particles of 1.2 nm in average diameter. Steady-state isotopic transient kinetic analysis was used to evaluate the intrinsic turnover frequency (TOF intr) and the surface coverage of carbon-containing species (theta COx) on the gold catalyst during CO oxidation at 1.2 atm total pressure and 296 K. The artifacts in the kinetic parameters caused by re-adsorption of product carbon dioxide were removed by varying the total flow rate. The values of TOF intr and theta COx determined from the intrinsic lifetime of surface intermediates at infinite flow rate were 1.6 s(-1) and 4.9%, respectively. The intrinsic turnover frequency was nearly independent of temperature, indicating a very low activation energy for the reaction. However, the rate was significantly accelerated by the presence of water.

Effects of Thiourea on Anodic Dissolution of Au and Surface Oxidation Behaviour in aq HClO4Studied by Means of an EQCN

Anodic dissolution of Au is facilitated by the presence of thiourea owing to formation of strongly complexed Au ions. The present paper reports studies of this process using cyclic voltammetry (CV), chronopotentiometry and chronoamperometry, usefully complemented by nanogravimetry employing an electrochemical quartz-crystal nanobalance (EQCN). The molar masses per faraday for Au dissolution were determined from EQCN measurements, coupled with information derived from CV, chronopotentiometry and chronoamperometry, and clearly indicate that Au becomes dissolved over the potential range 0.45—0.65 V vs RHE via a 1e− oxidation process in 0.5 M HClO4 solution containing thiourea. The peak potential for Au dissolution in the presence of thiourea is about 600 mV less positive than that in the presence of Br− or Cl− (1.20 V vs RHE for Br− and 1.39 V vs RHE for Cl−). The linear relationship between anodic peak currents at about 0.630 V vs RHE and square-root of the sweep rate indicates that the Au dissolution process is diffusion-controlled. The anodic current efficiency for Au dissolution is 93%.

Modification of Escherichia coli single-stranded DNA binding protein with gold nanoparticles for electrochemical detection of DNA hybridization

The unique binding event between Escherichia coli single-stranded DNA binding protein (SSB) and single-stranded oligonucleotides conjugated to gold (Au) nanoparticles is utilized for the electrochemical detection of DNA hybridization. SSB was attached onto a self-assembled monolayer (SAM) of single-stranded oligonucleotide modified Au nanoparticle, and the resulting Au-tagged SSB was used as the hybridization label. Changes in the Au oxidation signal was monitored upon binding of Au tagged SSB to probe and hybrid on the electrode surface. The amplified oxidation signal of Au nanoparticles provided a detection limit of 2.17 pM target DNA, which can be applied to genetic diagnosis applications. This work presented here has important implications with regard to combining a biological binding event between a protein and DNA with a solid transducer and metal nanoparticles.

Infrared spectra and structures of the stable CuH(2)(-), AgH(2)(-), AuH(2)(-), and AuH(4)(-) anions and the AuH(2) molecule.

Gold is noble, but excited gold is reactive. Reactions of laser-ablated copper, silver, and gold with H(2) in excess argon, neon, and pure hydrogen during condensation at 3.5 K give the MH molecules and the (H(2))MH complexes as major products and the MH(2)(-) and AuH(4)(-) anions as minor products. These new molecular anions are identified from matrix infrared spectra with isotopic substitution (HD, D(2), and H(2) + D(2)) and comparison to frequencies calculated by density functional theory. The stable linear MH(2)(-) anions are unique in that their corresponding neutral MH(2) molecules are higher in energy than M + H(2) and thus unstable to M + H(2) decomposition. Infrared spectra are observed for the bending modes of AuH(2), AuHD, and AuD(2) in solid H(2), HD, and D(2), respectively. The observation of square-planar AuH(4)(-) attests the stability of the higher Au(III) oxidation state for gold. The synthesis of CuH(2)(-) in solid compounds has potential for use in hydrogen storage.

Role of the Au oxidation state in the CO sensing mechanism of Au/iron oxide-based gas sensors

A study on the CO sensing mechanism of sensors based on Au-doped/iron oxide thick films is reported. Thick films were prepared from coprecipitated powders of Au/Fe 2O 3 calcined at temperatures between 100 and 400 °C. A detailed microstructural characterization by XRD, TEM and XPS has shown that nanometer sized gold particles with gold in a positive oxidation state are predominant after calcination of the powders at 100 °C. The mean size and the metallic character of the gold particles increase with increasing the calcination temperature. Electrical tests have shown an anomalous response, i.e. a conductivity decrease, to CO over the thick film calcined at 100 °C. Over films calcined at the temperature of 200 °C or above a normal response was found. It is suggested that different CO sensing mechanisms operate over these sensors. The anomalous response observed over the film annealed at the lowest temperature has been related to the participation of Au(III) ions in the CO sensing mechanism.

Electrochemical genosensor based on colloidal gold nanoparticles for the detection of Factor V Leiden mutation using disposable pencil graphite electrodes.

Electrochemical genosensors for the detection of the Factor V Leiden mutation from polymerase chain reaction (PCR) amplicons using the oxidation signal of colloidal gold (Au) is described. A pencil graphite electrode (PGE) modified with target DNA, when hybridized with complementary probes conjugated to Au nanoparticles, responded with the appearance of a Au oxide wave at approximately +1.20 V. Specific probes were immobilized onto the Au nanoparticles in two different modes: (a) Inosine-substituted probes were covalently attached from their amino groups at the 5' end using N-(3-dimethylamino)propyl)-N'-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysulfosuccinimide (NHS) as a coupling agent onto a carboxylate-terminated l-cysteine self-assembled monolayer (SAM) preformed on the Au nanoparticles, and (b) probes with a hexanethiol group at their 5' phosphate end formed a SAM on Au nanoparticles. The genosensor relies on the hybridization of the probes with their complementary targets, which are covalently immobilized at the PGE surface. Au-tagged 23-mer capture probes were challenged with the synthetic 23-mer target, 131-base single-stranded DNA or denatured 256-base polymerase chain reaction (PCR) amplicon. The appearance of the Au oxidation signal shortened the assay time and simplified the detection of the Factor V Leiden mutation from PCR amplified real samples. The discrimination between the homozygous and heterozygous mutations was also established by comparing the peak currents of the Au signals. Numerous factors affecting the hybridization and nonspecific binding events were optimized. The detection limit for the PCR amplicons was found to be as low as 0.78 fmol; thus, it is suitable for point-of-care applications.

Preparation, Spectroscopic Characterization, and Frontier MO Study of the Heteronuclear Luminescent [Pt(2)Au(2)(dmb)(2)(PPh(3))(4)](PF(6))(2) Cluster (dmb = 1,8-Diisocyano-p-menthane). A Cluster with a Formal Au(0)-Au(0) Bond Encapsulated inside a "Pt(2)(dmb)(2)(2+) " Fragment.

The title compound is prepared from the direct reaction of Pt(2)(dba)(3) (dba = dibenzylideneacetone) and [Au(PPh(3))(2)](PF(6)) in the presence of 1,8-diisocyano-p-methane (dmb), with Pt(2)(dmb)(2)Cl(2), [Pt(4)(dmb)(4)(PPh(3))(2)](PF(6))(2), and (PPh(3))AuCl being formed as parallel products. X-ray crystallography reveals the presence of a quasi-linear PPh(3)Au-AuPPh(3) fragment encapsulated inside a "Pt(2)(dmb)(2)(2+)" ring which is axially coordinated with two PPh(3) ligands. The d(AuAu) is 2.5977(6) Å and is indicative of a strong Au-Au single bond. The IR nu(CN) data reveal that the Pt oxidation state is I, which places the Au oxidation state at 0. The PtAu distances are 2.8422(5) and 2.8082(5) Å. The Raman-active nu(Au(2)), nu(PtAu) (b(2g) + a(g)), nu(PtP), nu(AuP), and nu(PtC) are found at 121.2, approximately 100, 85.5, 162.1, 183.1, and 457.2, and 440.9 cm(-)(1), respectively. The PtAu (0.67 mdyn Å(-)(1)) and Au(2) (1.21 mdyn Å(-)(1)) force constants (F) confirm the presence of medium PtAu and strong Au(2) bonding interactions. The absorption spectra are characterized by strong bands at lambda(max) (epsilon, M(-1) cm(-1)) at 316 (32 300), 366 (37 800), and 418 nm (21 500) and lower intensity features at 516 (2860) and 655 nm (834). The cluster is luminescent at low temperatures (solid and frozen glasses), and in the solid state at room temperature, and exhibits an emission band at approximately 875 nm, and an emission lifetime, tau(e), of 4.4 +/- 0.4 ns (solvent = butyronitrile, T = 77 K).

A study of ethylamine at a gold rotating ring‐disk electrode using pulsed electrochemical detection at the ring

AbstractLinear scan (cyclic) voltammetry at the disk with simultaneous pulsed electrochemical detection (PED) at the ring of a rotated ring‐disk electrode (RRDE) is demonstrated to be applicable for studies of the complex anodic behavior of ethylamine at gold electrodes in 0.10 M NaOH. The oxidation of ethylamine at the disk occurs during positive scans concomitantly with formation of surface oxide (Au → AuOH → AuO). However, the final oxide‐covered surface (AuO) is inert for further ethylamine oxidation. Data obtained at the RRDE demonstrate that the total ethylamine signal at the disk is composed of simultaneous contributions from: oxidative desorption of ethylamine preadsorbed at the oxide‐free Au surface and oxidation of ethylamine transported to the disk simultaneously with oxide formation. Based on ring‐disk data, preadsorbed ethylamine is estimated to correspond to a fractional surface coverage of 0.7 ± 0.1 monolayer for 10 to 60 μM ethylamine. Of this coverage, ca. 75% corresponds to ethylamine coadsorbed reversibly with OH− and 25% to ethylamine adsorbed irreversibly by a mechanism concluded to be chemisorption.

Thin-layer electrochemical studies of the underpotential deposition of cadmium and tellurium on polycrystalline Au, Pt and Cu electrodes

Thin-layer electrochemical studies of the underpotential deposition (UPD) of Cd and Te on polycrystalline Au, Pt, and Cu substrates have been performed. These studies were done in order to investigate the initial stages of the electrodeposition of CdTe. Tellurium deposition on Cu electrodes is very rapid at potentials between hydrogen evolution and Cu dissolution; as a result, the amount of electrodeposited Te cannot be suitably controlled with potential. Subsequent removal of Te on Cu also proved difficult by standard electrochemical cleaning procedures. Tellurium UPD and stripping on Pt occurred simultaneously with Pt oxide reduction and Pt oxidation, respectively. In addition, cadmium UPD on Pt is ill-defined, resulting in three peaks overlapping with the hydrogen wave voltammetry. It is presumed that the hydrogen waves are suppressed by the deposited Cd, although this is not definite. The most informative results were obtained with Au because of its broad double-layer window, which is free of complications from surface-specific faradaic reactions. Deposition of Te from TeO 2 solutions on Au was shown to require 3.9 ± 0.1 electrons per deposited Te. A substantial loss of electrodeposited Te was observed when the potential was cycled into the oxidation region on both the Au and Pt electrodes. Quantitation of the charge on Au indicated this loss was the result of oxidation of the Te(IV) to a Te(VI) compound which is difficult to reduce back to Te(IV) prior to hydrogen evolution on Au or Pt. At potentials between Au oxidation and Te UPD, the soluble Te species, HTeO + 2, was shown to adsorb reversibly on the Au surface. In studies of the alternated deposition of Cd and Te, initially deposited Cd is displaced by Te at potentials positive of −0.35 V. Subsequent UPD of Cd on the Te-covered Au resulted in one Cd atom for each deposited Te.

Stochastically-gated surface processes involving anions in oxidation of Au: time-resolution of processes down to 0.25% coverages and 50 μs time-scales

The mechanism of electrochemical surface oxidation of noble metals is compared with the oxidation of metals by gas-phase oxygen. In the presence of water, the role of preadsorbed anions of the electrolyte and of control of the potential across the interface, which is possible at electrodes, are discussed, including stochastically-gated oxide film growth. Time resolution of the initial stages of Au oxidation in which OH species are electrodeposited amongst chemisorbed anions in a surface array and become transformed, in time, to a quasi-2-dimensional phase oxide with anion desorption, can be made down to 0.25% coverage by OH and to times of ca 100 μs. The transformed species are reducible in two well resolved stages, both of which are substantially more stable, as measured by the Gibbs energies for their reduction, than the initial 2-D array from which they originated. The growth of the transformed species and the decrease of the coverage by the reversibly deposited OH's from which these species originate, are each logarithmic in time of growth. This behaviour is treated in terms of time-dependent changes of the surface-potential component of the metal—solution pd due to OH—M and O—M stochastically-gated place-exchange. The treatment is shown to lead to a direct logarithmic growth law having characteristic behaviour in agreement with experiment.

Perturbed angular-correlation experiments on 111In in oxidized fcc metals and their oxides.

The perturbed angular correlation (PAC) method has been employed to study the hyperfine interaction of the 245-keV state in $^{111}\mathrm{Cd}$, following $^{111}\mathrm{In}$ implantation into the fcc metals Ag, Al, Cu, Ni, Pd, Au, and Pt and subsequent oxidation. Broad quadrupole frequency distributions around a peak frequency 〈${\ensuremath{\omega}}_{1}$〉=160 MHz were found in all systems and attributed to oxygen trapping at $^{111}\mathrm{In}$. The fraction of oxidized $^{111}\mathrm{In}$ increases with the oxidation temperature in such a way that about 50% of the implanted In ions have trapped oxygen at 60% of the melting temperature of the host. An interpretation of these frequency distributions has been attempted on the basis of PAC measurements for $^{111}\mathrm{In}$ implanted into the metal oxides AgO, ${\mathrm{Ag}}_{2}$O, and ${\mathrm{In}}_{2}$${\mathrm{O}}_{3}$. In these systems, well-defined electric field gradients have been found which can be related to the respective crystallographic structures. In addition, the magnetic hyperfine interaction of $^{111}\mathrm{In}$ in antiferromagnetic NiO proves substitutional implantation.

Au(I)Au(II) and Au(I)Au(III) oxidation in ylide complexes with chlorinating agents

The gold(I) dimethylphosphonium-bis-methylide dimer 1a is converted into the AuAu-bonded gold (II) complexes 2a, 2b on addition of 1,2-dichloro- or 1,2,-dibromo-ethane respectively. Ethylene is eliminated in this oxidative addition process. With oxalyl or thionyl chloride the gold(III) complex 3a is obtained and no gold(II) intermediate can be observed. ortho-Dichlorobenzene and sym-tetrachloro-ethane give no reaction with 1a. Oxidative addition of dichloromethane to the gold(I)-di-t-butylphosphonium-bis-methylide dimer 1c yields the AuCH 2Au-bridged Au(III) complex 4c, analogous to the (P,P)-tetramethyl homologues (4) described previously.