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International audience; A series of triiron clusters [Fe3(CO)5(2-dppe)(µ-pdtR2)(µ-pdt)] featuring different combination of dithiolate bridges have been prepared by using dinuclear and mononuclear precursors, [Fe2(CO)6(µ-xdt)] (xdt = pdt, pdtEt2, pdtBn2, adtBn) and [Fe(CO)2(2-dppe)(2-pdt)]. Novel triiron compounds, featuring sterically crowded dithiolate bridges (pdtEt2, pdtBn2), were spectroscopically and structurally characterized. Their protonation and redox behaviours are discussed. The effect of the dithiolate bridges on the electrochemical properties (oxidation and reduction) of the complexes [Fe3(CO)5(2-dppe)(µ-xdt)(µ-pdt)] has been examined by cyclic voltammetry and rationalized by DFT calculations. Studies of the protonation of these species and their proton reduction behaviour were considered.

International audience; The synthesis, characterization, and protonation of [Fe2(CO)6{(μ-SCH2)2(Et)P═O}] (1) using the moderately strong acid CF3CO2H (pKaMeCN = 12.7) are reported. Digital simulations of the cyclic voltammetry of 1 in the presence of CF3CO2H and DFT calculations have allowed us to obtain a detailed mechanistic picture of the processes underlying the catalytic hydrogen evolution reaction (HER) that 1 can mediate. Moreover, DFT has shed light on the role of the P═O functionality in the whole catalytic cycle of proton reduction. The reductive behavior of 1 features a double electron transfer with potential inversion, which is associated with deep structural rearrangement of the catalyst. The double reduction appears also functional to the intramolecular proton transfer from the P═O group to the diiron core, a crucial process for the H+/H– heterocoupling yielding H2. The key intermediate for the H2 formation and release is predicted to be a 3H+/3e– species, in which P═O is perfectly poised to shuttle protons from solution to the Fe–H–Fe moiety. Therefore, the R-P═O bridgehead installed in a dithiolato linker of a diiron core proves a valid and versatile alternative to the natural nitrogen-based Fe2 strap.

A novel complex featuring a mesoionic carbene [Fe2(CO)5(trz)(?-pdt)] (1) (trz = 1-phenyl-l,3-methyl,4-butyl-1,2,3-triazol-5-ylidene), was synthesized and spectroscopically and structurally characterized. The reductive behaviour of this compound in the presence and in the absence of acid (CH3CO2H) was examined by cyclic voltammetry (CV) that revealed the lack of efficient activity towards proton reduction.

International audience; Electrochemical oxidation of the complex [Fe2(CO)4(κ2‐dmpe)(µ‐adtBn)] (adtBn = (SCH2)2NCH2C6H5, dmpe = Me2PCH2CH2PMe2) (1) has been studied by cyclic voltammetry (CV) in acetonitrile and in dichloromethane in presence of various substrates L (L =MeCN, trimethylphosphite, isocyanide). The oxidized species, [1‐MeCN](PF6)2, [1‐(P(OMe)3)2](PF6)2 and [1‐(RNC)4](PF6)2 (R = tButyl, Xylyl), have been prepared and characterized by IR, NMR spectroscopies and, excepted [1‐MeCN](PF6)2, by X‐ray diffraction analysis. The crystallographic structures of the new FeIIFeII complexes reveal in any case that the association of one additional ligand (P(OMe)3 or RNC) occurs and, according to the nature of the substrates, further substitutions of one or three carbonyl groups, by P(OMe)3 or RNC, respectively, arise. Density functional theory (DFT) calculations have been performed for elucidating and discriminating, in each case, the mechanisms leading to the corresponding oxidized species. Moreover, the different degree of ligand substitution in the diiron core has been theoretically rationalized.

International audience; Electrochemical studies of [Fe2(CO)4(κ2-dmpe)(μ-dithiolate)] (dithiolate=adtBn, pdt) and density functional theory (DFT) calculations reveal the striking influence of an amine functionality in the dithiolate bridge on their oxidative properties. [Fe2(CO)4(κ2-dmpe)(μ-adtBn)] (1) undergoes two one-electron oxidation steps, with the first being partially reversible and the second irreversible. When the adtBn bridge is replaced with pdt, a shift of 60 mV towards more positive potentials is observed for the first oxidation whereas 290 mV separate the oxidation potentials of the two cations. Under CO, oxidation of azadithiolate compound 1 occurs according to an ECE process whereas an EC mechanism takes place for the propanedithiolate species 2. The dication species [1-CO]2+ resulting from the two-electron oxidation of 1 has been spectroscopically and structurally characterized. The molecular details underlying the reactivity of oxidized species have been explored by DFT calculations. The differences in the behaviors of 1 and 2 are mainly due to the presence, or not, of favored interactions between the dithiolate bridge and the diiron site depending on the redox states, FeIFeII or FeIIFeII, of the complexes.

cited By 27; International audience; A comparative study of the behavior of different sorts of three-phase electrodes applied for assessing the thermodynamics and kinetics of the ion transfer across the liquid |liquid (L|L) interface is presented. Two types of three-phase electrodes are compared, that is, a paraffin-impregnated graphite electrode at the surface of which a macroscopic droplet of an organic solvent is attached and an edge pyrolytic graphite electrode partly covered with a very thin film of the organic solvent. The organic solvent contains either decamethylferrocene or lutetium bis(tetra-tert-butylphthalocyaninato) as a redox probe. The role of the redox probe, the type of the electrode material, the mass transfer regime, and the effect of the uncompensated resistance are discussed. The overall electrochemical process at both three-phase electrodes proceeds as a coupled electron-ion transfer reaction. The ion transfer across the L|L interface, driven by the electrode reaction of the redox compound at the electrode|organic solvent interface, is independent of the type of redox probe. The ion transfer proceeds without involving any chemical coupling between the transferring ion and the redox probe. Both types of three-phase electrodes provide consistent results when applied for measuring the energy of the ion transfer. Under conditions of square-wave voltammetry, the coupled electron-ion transfer at the three-phase electrode is a quasireversible process, exhibiting the property known as "quasireversible maximum". The overall electron-ion transfer process at the three-phase electrode is controlled by the rate of the ion transfer. It is demonstrated for the first time that the three-phase electrode in combination with the quasireversible maximum is a new tool for assessing the kinetics of the ion transfer across the L|L interface. © 2005 American Chemical Society.

Antimony is a naturally occurring element. It belongs to group 15 of the periodic table of the elements. Antimony can exist in a variety of oxidation states (–III, 0, III, V) but it is mainly found in two oxidation states (III and V) in environmental, biological, and geochemical samples. Although antimony was already known to the ancients, it is still often overlooked, both as an element of environmental concern and as a subject for study, probably because of its lower abundance and the relative insolubility of most of its compounds. This is reflected in the poor standard of existing data on the behavior of antimony in natural waters. However, interest in the study of this element seems to be growing and an increasing number of papers on the subject are being published. A useful series of comprehensive reviews on antimony in the environment has recently been published (1, 2).

cited By 3; International audience; Cathodic adsorptive stripping voltammetry is one of the most sensitive analytical methods for ultratrace analysis. The detection limit is usually lower than 10-9 mol/L. Most adsorptive stripping procedures have been focused on the one ligand/one analyte approach. In order to reduce analysis time and sample volume, the possibility of simultaneously determining several metals by cathodic stripping voltammetry using a mixture of ligands was explored, e.g., by Colombo and van den Berg (1997). Here, we describe a new procedure for quantifying chromium and copper using 2,2′-bipyridine and 8-hydroxyquinoline (oxine). The effect of various operational parameters such as buffer type, ligand concentration, potential and time collection were assessed and optimized. Possible interferences by trace metals and organic matter were also investigated. Applicability for fresh water is illustrated. © Springer-Verlag 2003.

The [FeFe] hydrogenase is a highly sophisticated enzyme for the synthesis of hydrogen via a biological route. The rotated state of the H-cluster in the [FeIFeI] form was found to be an indispensable criteria for an effective catalysis. Mimicking the specific rotated geometry of the [FeFe] hydrogenase active site is highly challenging as no protein stabilization is present in model compounds. In order to simulate the sterically demanding environment of the nature's active site, the sterically crowded meso-bis(benzylthio)diphenylsilane (2) was utilized as dithiolate linker in an [2Fe2S] model complex. The reaction of the obtained hexacarbonyl complex 3 with 1,2-bis(dimethylphosphino)ethane (dmpe) results three different products depending on the amount of dmpe used in this reaction: [{Fe2(CO)5{μ-(SCHPh)2SiPh2}}2(μ-dmpe)] (4), [Fe2(CO)5(κ2-dmpe){μ-(SCHPh)2SiPh2}] (5) and [Fe2(CO)5(μ-dmpe){μ-(SCHPh)2SiPh2}] (6). Interestingly, the molecular structure of compound 5 shows a [FeFe] subsite comprising a semi-rotated conformation, which was fully characterized as well as the other isomers 4 and 6 by elemental analysis, IR and NMR spectroscopy, X-ray diffraction analysis (XRD) and DFT calculations. The herein reported model complex is the first example so far reported for [FeIFeI] hydrogenase model complex showing a semi-rotated geometry without the need of stabilization via agostic interactions (Fe⋯H-C). This journal is

The utilization of light and inexpensive catalysts to afford hydrogen represents a huge challenge. Following our interest in silicon-containing [FeFe]-hydrogenase ([FeFe]-H2ase) mimics, we report a new model approach for a photocatalytic [FeFe]-H2ase mimic 1, which contains a 1-silafluorene unit as a photosensitizer. Thereby, the photoactive ligand is linked to the [2Fe2S] cluster through S–CH2–Si bridges. Photochemical H2 evolution experiments were performed and revealed a turnover number (TON) of 29. This is the highest reported photocatalytic efficiency for an [FeFe]-H2ase model complex in which the photosensitizer is covalently linked to the catalytic center.

Rotated geometry: The first example of a dinuclear iron(I)-iron(I) complex featuring a fully rotated geometry related to the active site of [Fe-Fe] hydrogenase is reported (see figure). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

International audience; The silver-based MOF material Ag3(3-phosphonobenzoate) was evaluated as a bactericidal material. A sustainable release of Ag+, which was quantified by cathodic stripping voltammetry, was responsible for bactericidal activity against the 6 bacterial strains tested.

cited By 5; International audience; Despite its importance for understanding the behaviour of antimony in the environment, the oxidation kinetics of Sb(III) with natural oxidants is still not well understood. We have studied the oxidation of Sb(III) by hydrogen peroxide on a time scale of hours in the presence of some trace metals, Cu(II), Mn(II), Zn(II) and Pb(II), under pH and concentration conditions close to natural ones. The effects that these trace metals have on Sb(III) oxidation by hydrogen peroxide vary. Zn(II) had no catalytic effect at all, but Cu(II), Mn(II) and Pb(II) did, though their effects were not uniform. Cu(II) significantly accelerated the reaction, which remained first-order with respect to Sb(III) at any Cu(II) concentration tested. Pb(II) and Mn(II) also enhanced the reaction rates, but the apparent order of the reaction with respect to Sb(III) changed to two. The trace metal effect observed was concentration dependent for Pb(II). The addition of the hydroxyl radical scavenger 2-propanol suggests that the trace metal catalytic effect observed involves the action of hydroxyl radicals, but that they are not responsible for the oxidation of Sb(III) by H2O2 in the absence of trace metals. The fact that Sb(III) can be oxidized by hydroxyl radicals present in water, even if it is not capable of producing them, has important environmental implications because hydroxyl radicals are known to be abundant in many natural waters such as seawater, humic-rich surface waters or rainwater. © The Royal Society of Chemistry 2005.

cited By 9; International audience; The possible occurrence of polluted aerosols formed by a bubbling mechanism from hydrocarbon-rich aqueous surface layers was investigated in laboratory through the determination of hydrocarbon adsorption from diluted solutions. Benzene and cyclohexane both exhibited positive adsorption. Further to our previous demonstration of lead nitrate coadsorption with benzene near the solubility limit (Sadiki et al., 2003. Atmospheric Environment 37, 3551-3559) the present study revealed a positive coadsorption of lead nitrate with both hydrocarbons, even in diluted solutions. The use of the bubble-column (Wan, Tokunaga, 1998. Environment Science and Technology 32, 3293-3298) as an experimental tool is discussed as well as the physico-chemical mechanisms involved in adsorption and coadsorption processes with their impact on the environment. © 2005 Elsevier Ltd. All rights reserved.

cited By 39; International audience; Knowledge of antimony redox kinetics is crucial in understanding the impact and fate of Sb in the environment and optimizing Sb removal from drinking water. The rate of oxidation of Sb(III) with H2O 2 was measured in 0.5 mol L-1 NaCl solutions as a function of [Sb(III)], [H2O2], pH, temperature, and ionic strength. The rate of oxidation of Sb(III) with H2O2 can be described by the general expression: -d[Sb(III)]/dt = k[Sb(III)][H 2O2][H+]-1 with log k= -6.88 (±0.17) [k: min-1]. The undissociated Sb(OH)3 does not react with H2O2: the formation of Sb(OH) 4 - is needed for the reaction to take place. In a mildly acidic hydrochloric acid medium, the rate of oxidation of Sb(III) is zeroth order with respect to Sb(III) and can be described by the expression -d[Sb(III)]/dt = k[H2O2][H+][Cl-] with log k = 4.44 (±0.05) [k: L2 mol-2 min -1]. The application of the calculated rate laws to environmental conditions suggests that Sb(III) oxidation by H2O2 may be relevant either in surface waters with elevated H2O2 concentrations and alkaline pH values or in treatment systems for contaminated solutions with millimolar H2O2 concentrations.

cited By 17; International audience; This study attempts to evidence a physical interfacial mechanism for the passing of some non-volatile harmful molecules from water, where they are dissolved, to the atmosphere. The idea developed here is that an organic substance, at its solubility limit, forms a surface layer whose properties induce the coadsorption of another dissolved substance; both are then able to pass to the atmosphere by a bubbling mechanism. Experiments were made with benzene close of its solubility limit in an aqueous solution of lead nitrate, which is non-volatile and normally does not adsorb at water surface. Coadsorption really occurred. The impact of such a mechanism on the environment is discussed. © 2003 Elsevier Science Ltd. All rights reserved.

cited By 5; International audience; The reduction process of molybdenum in the presence of fulvic acids and phenanthroline was investigated by square-wave voltammetry (SWV), The mixed-ligand complex of molybdenum exhibits a pronounced tendency to adsorb onto the mercury electrode surface. The electrode reaction proceeds as a surface process in which both components of the redox couple are firmly confined to the electrode surface. The kinetics of the electrode reaction is studied utilizing the properties of "split SW peaks" and "quasireversible maximum". The kinetic parameters obtained with two different square-wave voltammetric methods are in good agreement. In 0.5 mol/L NaCl solution with pH 2.5 the kinetic parameters are: standard rate constant ks = 8 ± 2 s-1, cathodic electron transfer coefficient α = 0.41 ± 0.05, and number of exchanged electrons n =2. The SW kinetic measurements are confirmed by cyclic voltammetric method.

International audience; A procedure for the determination of selenium species in seawater is proposed. The speciation scheme is based on different sample treatments followed by the quantification of Se(IV) by differential pulse cathodic stripping voltammetry. To remove the organic matter present in seawater which interferes in the electrochemical step a XAD-2 resin is used. So the selenite concentration can be directly determined. After passage through an IRA 400, selenide is collected in the percolated solution. Following conversion into the tetravalent state, selenium is determined. UV photolysis at basic pH is used to convert all the selenium species to Se(IV) which is the electroactive species. The procedure is applied to seawater samples.