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2021



  • M. Balas, S. Beaudoin, A. Proust, F. Launay, et R. Villanneau, « Advantages of Covalent Immobilization of Metal-Salophen on Amino-Functionalized Mesoporous Silica in Terms of Recycling and Catalytic Activity for CO2 Cycloaddition onto Epoxides », European Journal of Inorganic Chemistry, vol. 2021, nᵒ 16, p. 1581-1591, 2021.
    Résumé : NiII and MnIII Schiff base complexes (Salophen-Ni and Salophen-MnCl) bearing a pending carboxylic group were prepared and characterized. Both complexes were grafted onto a mesoporous amino-functionalized SBA-15 silica, by formation of an amide function between the propylamine groups of the support and the carboxylic acid functions of the salophen ligand (corresponding respective to 1.30 wt.% of Ni and 1.06 wt.% of Mn). The co-catalytic behaviour of the free and grafted complexes was then evaluated in the CO2 cycloaddition reaction onto styrene oxide, using tetra-butylammonium bromide (n−Bu4NBr) as the main catalyst. In homogeneous conditions, the MnIII Schiff base complex and the NiII one, to a lesser extent, behave as efficient co-catalysts for this reaction (styrene conversion of 100 % and 65 % respectively after 3 h at 120 °C, under 15 bars of CO2). Upon immobilization at the surface of the amino-functionalized SBA-15, we showed that the co-catalytic activity of the less efficient one, i. e. Ni2+ salophen complex, could be enhanced (reaching a full conversion after 7 h), hence highlighting a potential synergistic effect between the unused amine functions of the support and the Ni2+ salophen co-catalyst. Both salophen complexes were successfully re-used in homogeneous conditions or after their immobilization without any appreciable loss of activity. This work is only a first step towards a completely heterogeneous catalytic system, in which the tetraalkylammonium halide catalyst and the metal-salophen co-catalyst will both be covalently anchored on the same support.
    Mots-clés : CO2 valorization, Cyloaddition, E-POM, Hybrid catalysts, Mesoporous materials, POLE 2, Salen derivatives.
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  • M. Balas, L. K/Bidi, F. Launay, et R. Villanneau, « Chromium-Salophen as a Soluble or Silica-Supported Co-Catalyst for the Fixation of CO2 Onto Styrene Oxide at Low Temperatures », Frontiers in Chemistry, vol. 9, p. 765108, oct. 2021.
    Résumé : Addition of a soluble or a supported Cr III -salophen complex as a co-catalyst greatly enhances the catalytic activity of Bu 4 NBr for the formation of styrene carbonate from styrene epoxide and CO 2 . Their combination with a very low co-catalyst:Bu 4 NBr:styrene oxide molar ratio = 1:2:112 (corresponding to 0.9 mol% of Cr III co-catalyst) led to an almost complete conversion of styrene oxide after 7 h at 80°C under an initial pressure of CO 2 of 11 bar and to a selectivity in styrene carbonate of 100%. The covalent heterogenization of the complex was achieved through the formation of an amide bond with a functionalized {NH 2 }-SBA-15 silica support. In both conditions, the use of these Cr III catalysts allowed excellent conversion of styrene already at 50°C (69 and 47% after 24 h, respectively, in homogeneous and heterogeneous conditions). Comparison with our previous work using other metal cations from the transition metals particularly highlights the preponderant effect of the nature of the metal cation as a co-catalyst in this reaction, that may be linked to its calculated binding energy to the epoxides. Both co-catalysts were successfully reused four times without any appreciable loss of performance.
    Mots-clés : E-POM, POLE 2.
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  • E. Benazzi, J. Karlsson, Y. Ben M'Barek, P. Chabera, S. Blanchard, S. Alves, A. Proust, T. Pullerits, G. Izzet, et E. A. Gibson, « Acid-triggering of light-induced charge-separation in hybrid organic/inorganic molecular photoactive dyads for harnessing solar energy », Inorganic Chemistry Frontiers, vol. 8, nᵒ 6, p. 1610-1618, 2021.
    Résumé : H + modulated charge-transfer in photoexcited covalently linked W and Mo Keggin-bodipy conjugates is demonstrated using transient absorption spectroscopy and photoluminescence. Adding acid switches on (W) or accelerates (Mo) charge separation. , H + modulated charge-transfer in photoexcited covalent polyoxometalate-bodipy conjugates is described. The hybrid organic/inorganic molecular photoactive dyads are based on Keggin-type polyoxometalates (POMs, where K M = [PM 11 O 39 ] and M = Mo or W) covalently grafted via an organotin linker to a bodipy (BOD) photosensitizer. The relative potentials of the photosensitizer and POM are aligned such that light-induced electron transfer from BOD to POM is permitted for the polyoxomolybdate KMoSn[BOD] but not effective for the polyoxotungstate analogue KWSn[BOD] . In both cases, the addition of acid shifts the redox potential of the POM only, to increase the driving force for electron transfer. This leads to charge-separation being switched on for KWSn[BOD] in the presence of acid. The addition of acid to KMoSn[BOD] accelerates charge-separation by an order of magnitude (from 2 ns to 200 ps) and is accompanied by a deceleration of charge recombination, leading to a charge-separated state lifetime of up to 1.3 μs. This behaviour is consistent with proton coupled electron transfer, which has previously been observed electrochemically for POMs, but this study shows, for the first time, the impact of protonation on photoinduced electron transfer.
    Mots-clés : CSOB, E-POM, POLE 2, POLE 3.
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  • A. Gillet, S. Cher, M. Tassé, T. Blon, S. Alves, G. Izzet, B. Chaudret, A. Proust, P. Demont, F. Volatron, et S. Tricard, « Polarizability is a key parameter for molecular electronics », Nanoscale Horizons, vol. 6, nᵒ 3, p. 271-276, mars 2021.
    Résumé : Identifying descriptors that govern charge transport in molecular electronics is of prime importance for the elaboration of devices. The effects of molecule characteristics, such as size, bulkiness or charge, have been widely reported. Herein, we show that the molecule polarizability can be a crucial parameter to consider. To this end, platinum nanoparticle self-assemblies (PtNP SAs) are synthesized in solution, including a series of polyoxometalates (POMs). The charge of the POM unit can be modified according to the nature of the central heteroatom while keeping its size constant. POM hybrids that display remote terminal thiol functions strongly anchor the PtNP surface to form robust SAs. IV curves, recorded by conductive AFM, show a decrease in Coulomb blockade as the dielectric constant of the POMs increases. In this system, charge transport across molecular junctions can be interpreted as variations in polarizability, which is directly related to the dielectric constant.
    Mots-clés : E-POM, POLE 2.
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  • S. Mabrouk, H. Rinnert, L. Balan, S. Blanchard, J. Jasniewski, G. Medjahdi, R. B. Chaabane, et R. Schneider, « Aqueous synthesis of highly luminescent ternary alloyed Mn-doped ZnSeS quantum dots capped with 2-mercaptopropionic acid », Journal of Alloys and Compounds, vol. 858, p. 158315, mars 2021.
    Résumé : Highly photoluminescent and water dispersible ternary alloyed Mn-doped ZnSeS and core/shell Mn:ZnSeS/ZnS quantum dots (QDs) with pure dopant emission were synthesized through a simple aqueous route using thiolactic acid (2-MPA) as a capping ligand. Transmission electron microscopy and X-ray diffraction show that Mn:ZnSeS nanocrystals are of spherical shape, with a diameter of 2.4 nm and a cubic zinc blende structure. With the overcoating of the ZnS shell, the particle size increases to 3.7 nm, which confirms the epitaxial growth of the shell on Mn:ZnSeS cores. The photoluminescence (PL) quantum yield depends on the Mn loading and reaches 22% for Mn:ZnSeS cores doped with 10% Mn and 41% after the growth of ZnS at the surface of the cores due to the effective elimination of surface-trap states. Mn:ZnSeS QDs exhibit also long PL lifetimes (up to 681 μs) indicating that the emission originates from the spin forbidden Mn2+ 4T1 → 6A1 transition. Electron paramagnetic resonance and X-ray photoelectron spectroscopy results suggest that Mn2+ ions are located at the interface of core/shell Mn:ZnSeS/ZnS QDs. Further, the stability of Mn:ZnSeS/ZnS QDs was also investigated along with their transfer in organic phase using octanethiol.
    Mots-clés : 2-Mercaptopropionic acid, Core/shell Mn:ZnSeS/ZnS, E-POM, Mn-doped ZnSeS, Photoluminescence, POLE 2, Quantum dots, Stability.
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  • G. Toupalas, J. Karlsson, F. A. Black, A. Masip‐Sánchez, X. López, Y. Ben M'Barek, S. Blanchard, A. Proust, S. Alves, P. Chabera, I. P. Clark, T. Pullerits, J. M. Poblet, E. A. Gibson, et G. Izzet, « Tuning Photoinduced Electron Transfer in POM‐Bodipy Hybrids by Controlling the Environment: Experiment and Theory », Angewandte Chemie, vol. 133, nᵒ 12, p. 6592-6599, mars 2021.


  • ="csl-entry"> T. Zhang, A. Solé‐Daura, H. Fouilloux, J. M. Poblet, A. Proust, J. J. Carbó, et G. Guillemot, « Reaction Pathway Discrimination in Alkene Oxidation Reactions by Designed Ti-Siloxy-Polyoxometalates », ChemCatChem, vol. 13, nᵒ 4, p. 1220-1229, 2021.
    Résumé : Titanium complexes of silanol functionalized polyoxometalates (THA)3[SbW9O33(RSiO)3Ti(OiPr)] (Ti-SiloxPOMs) catalyze alkene oxidation with tert-butyl hydrogen peroxide (TBHP). However catalytic activity and product distribution in the oxidation of allylic alcohols are shown to depend on the steric surrounding generated by the SiloxPOM (R=tBu, iPr, nPr). Combined experimental and computational studies clarify how steric repulsions between the oxidant (tBu group) and the surrounding SiloxPOM govern the reaction pathways leading either to oxidation of the alcohol function (R=tBu) or to alkene epoxidation (R=nPr). Moreover, another consequence of this steric repulsive interactions is that outer-sphere mechanisms become competitive with the inner-sphere ones (coordination of allylic alcohol), whether for the oxidative dehydrogenation reaction or for the epoxidation reaction. In the case of unfunctionalized olefins (linear and cyclic), we show that reducing the bulkiness surrounding the active site leads to higher conversion to epoxide, emphasizing that these Ti-SiloxPOMs may behave as structural and functional models for metal single-site in Ti-Silicates.
    Mots-clés : alkene, DFT, E-POM, mechanistic study, oxidation, POLE 2, polyoxotungstates, titanium.
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2020



  • Y. Ben M’Barek, T. Rosser, J. Sum, S. Blanchard, F. Volatron, G. Izzet, R. Salles, J. Fize, M. Koepf, M. Chavarot-Kerlidou, V. Artero, et A. Proust, « Dye-Sensitized Photocathodes: Boosting Photoelectrochemical Performances with Polyoxometalate Electron Transfer Mediators », ACS Applied Energy Materials, vol. 3, nᵒ 1, p. 163-169, janv. 2020.


  • M. S. Centellas, M. Piot, R. Salles, A. Proust, L. Tortech, D. Brouri, S. Hupin, B. Abécassis, D. Landy, C. Bo, et G. Izzet, « Exploring the self-assembly of dumbbell-shaped polyoxometalate hybrids, from molecular building units to nanostructured soft materials », Chemical Science, vol. 11, nᵒ 40, p. 11072-11080, oct. 2020.
    Résumé : The formation of hierarchical nanostructures using preformed dumbbell-like species made of covalent organic–inorganic polyoxometalate (POM)-based hybrids is herein described. In this system, the presence of charged subunits (POM, metal linkers, and counter ions) in the complex molecular architecture can drive their aggregation, which results from a competition between the solvation energy of the discrete species and intermolecular electrostatic interactions. We show that the nature of the POM and the charge of the metal linker are key parameters for the hierarchical nanoorganization. The experimental findings were corroborated with a computational investigation combining DFT and molecular dynamics simulation methods, which outlines the importance of solvation of the counter ion and POM/counter ion association in the aggregation process. The dumbbell-like species can also form gels, in the presence of a poorer solvent, displaying similar nanoorganization of the aggregates. We show that starting from the designed molecular building units whose internal charges can be controlled by redox trigger we can achieve their implementation into soft nanostructured materials through the control of their supramolecular organization.
    Mots-clés : E-POM, POLE 2.
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  • S. Dhifaoui, M. Hajji, T. Guerfel, V. Marvaud, J. - C. Daran, I. Turowska-Tyrk, R. Bel-Hadj-Tahar, et H. Nasri, « Experimental and computational studies on the structure and properties of a novel low-spin iron(III) macrocyclic complex », Molecular Crystals and Liquid Crystals, vol. 702, nᵒ 1, p. 92-109, mai 2020.


  • B. Doistau, L. Benda, J. - L. Cantin, O. Cador, F. Pointillart, W. Wernsdorfer, L. - M. Chamoreau, V. Marvaud, B. Hasenknopf, et G. Vives, « Dual switchable molecular tweezers incorporating anisotropic MnIII–salphen complexes », Dalton Transactions, vol. 49, nᵒ 26, p. 8872-8882, juill. 2020.
    Résumé : An alternative strategy for the synthesis of terpyridine based switchable molecular tweezers has been developed to incorporate anisotropic Mn(III)–salphen complexes. The free ligand was synthesized using a building block strategy based on Sonogashira coupling reactions and was then selectively metalated with manganese in a last step. The conformation of the tweezers was switched from an open ‘W’ shaped form to a closed ‘U’ form by Zn(II) coordination to the terpyridine unit bringing the two Mn–salphen moieties in close spatial proximity as confirmed by X-ray crystallography. An alternate switching mechanism was observed by the intercalation of a bridging cyanide ligand between the two Mn–salphen moieties that resulted in the closing of the tweezers. These dual stimuli are attractive for achieving multiple controls of the mechanical motion of the tweezers. A crystallographic structure of unexpected partially oxidized closed tweezers was also obtained. One of the two Mn–salphen moieties underwent a ligand-centered oxidation of an imino to an amido group allowing an intramolecular Mn–Oamide–Mn linkage. The magnetic properties of the manganese(III) dimers were investigated to evaluate the magnetic exchange interaction and analyze the single molecule magnet behavior.
    Mots-clés : E-POM, GOBS, POLE 2, POLE 3.
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  • A. Generosi, M. Guaragno, Q. Zhu, A. Proust, N. T. Barrett, L. Tortech, et B. Paci, « In-Situ Energy Dispersive X-ray Reflectivity Applied to Polyoxometalate Films: An Approach to Morphology and Interface Stability Issues in Organic Photovoltaics », Symmetry, vol. 12, nᵒ 8, p. 1240, févr. 2020.
    Résumé : Organic solar cells, characterized by a symmetrical regular layered structure, are very promising systems for developing green, low cost, and flexible solar energy conversion devices. Despite the efficiencies being appealing (over 17%), the technological transfer is still limited by the low durability. Several processes, in bulk and at interface, are responsible. The quick downgrading of the performance is due to a combination of physical and chemical degradations. These phenomena induce instability and a drop of performance in working conditions. Close monitoring of these processes is mandatory to understand the degradation pathways upon device operation. Here, an unconventional approach based on Energy Dispersive X-ray Reflectivity (ED-XRR) performed in-situ is used to address the role of Wells–Dawson polyoxometalate (K6-P2W18O62, hereafter K6-P2W18) as hole transporting layer in organic photovoltaics. The results demonstrate that K6-P2W18 thin films, showing ideal bulk and interface properties and superior optical/morphological stability upon prolonged illumination, are attractive candidates for the interface of durable OPV devices.
    Mots-clés : E-POM, in-situ X-ray characterization, organic photovoltaics, POLE 2, polyoxymetalate functional materials, thin films structure and morphology, time resolved EDXR.
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  • W. Hamouda, A. Pancotti, C. Lubin, L. Tortech, C. Richter, T. Mikolajick, U. Schroeder, et N. Barrett, « Physical chemistry of the TiN/Hf0.5Zr0.5O2 interface », Journal of Applied Physics, vol. 127, nᵒ 6, p. 064105, févr. 2020.
    Résumé : Ferroelectric hafnia-based thin films are promising candidates for emerging high-density embedded nonvolatile memory technologies, thanks to their compatibility with silicon technology and the possibility of 3D integration. The electrode–ferroelectric interface and the crystallization annealing temperature may play an important role in such memory cells. The top interface in a TiN/Hf0.5Zr0.5O2/TiNTiN/Hf0.5Zr0.5O2/TiN<math display="inline" overflow="scroll" altimg="eq-00001.gif"> <mrow> <mi mathvariant="normal">TiN</mi></mrow> <mo>/</mo> <msub> <mrow> <mi mathvariant="normal">Hf</mi></mrow> <mrow> <mn>0.5</mn></mrow></msub> <msub> <mrow> <mi mathvariant="normal">Zr</mi></mrow> <mrow> <mn>0.5</mn></mrow></msub> <msub> <mrow> <mi mathvariant="normal">O</mi></mrow> <mn>2</mn></msub> <mo>/</mo> <mrow> <mi mathvariant="normal">TiN</mi></mrow></math> metal–ferroelectric–metal stack annealed at different temperatures was investigated with X-ray photoelectron spectroscopy. The uniformity and continuity of the 2 nm TiN top electrode was verified by photoemission electron microscopy and conductive atomic force microscopy. Partial oxidation of the electrode at the interface is identified. Hf is reduced near the top interface due to oxygen scavenging by the top electrode. The oxygen vacancy (VOVO<math display="inline" overflow="scroll" altimg="eq-00002.gif"> <msub> <mi>V</mi> <mrow> <mi mathvariant="normal">O</mi></mrow></msub></math>) profile showed a maximum at the top interface (0.71%) and a sharp decrease into the film, giving rise to an internal field. Annealing at higher temperatures did not affect the VOVO<math display="inline" overflow="scroll" altimg="eq-00003.gif"> <msub> <mrow> <mi mathvariant="normal">V</mi></mrow> <mrow> <mrow> <mi mathvariant="normal">O</mi></mrow></mrow></msub></math> concentration at the top interface but causes the generation of additional VOVO<math display="inline" overflow="scroll" altimg="eq-00004.gif"> <msub> <mrow> <mi mathvariant="normal">V</mi></mrow> <mrow> <mrow> <mi mathvariant="normal">O</mi></mrow></mrow></msub></math> in the film, leading to a decrease of the Schottky Barrier Height for electrons. The interface chemistry and n-type film doping are believed to be at the origin of several phenomena, including wake-up, imprint, and fatigue. Our results give insights into the physical chemistry of the top interface with the accumulation of defective charges acting as electronic traps, causing a local imprint effect. This may explain the wake-up behavior as well and also can be a possible reason of the weaker endurance observed in these systems when increasing the annealing temperature.
    Mots-clés : E-POM, POLE 2.
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  • M. Laurans, K. Trinh, K. Dalla Francesca, G. Izzet, S. Alves, E. Derat, V. Humblot, O. Pluchery, D. Vuillaume, S. Lenfant, F. Volatron, et A. Proust, « Covalent Grafting of Polyoxometalate Hybrids onto Flat Silicon/Silicon Oxide: Insights from POMs Layers on Oxides », ACS Applied Materials & Interfaces, vol. 12, nᵒ 42, p. 48109-48123, oct. 2020.
    Résumé : Immobilization of polyoxometalates (POMs) onto oxides is relevant to many applications in the fields of catalysis, energy conversion/storage, or molecular electronics. Optimization and understanding the molecule/oxide interface is crucial to rationally improve the performance of the final molecular materials. We herein describe the synthesis and covalent grafting of POM hybrids with remote carboxylic acid functions onto flat Si/SiO2 substrates. Special attention has been paid to the characterization of the molecular layer and to the description of the POM anchoring mode at the oxide interface through the use of various characterization techniques, including ellipsometry, AFM, XPS, and FTIR. Finally, electron transport properties were probed in a vertical junction configuration and energy level diagrams have been drawn and discussed in relation with the POM molecular electronic features inferred from cyclic-voltammetry, UV–visible absorption spectra, and theoretical calculations. The electronic properties of these POM-based molecular junctions are driven by the POM LUMO (d-orbitals) whatever the nature of the tether or the anchoring group.
    Mots-clés : CSOB, E-POM, MACO, POLE 1, POLE 2, POLE 3.
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  • O. Makrygenni, L. Vanmairis, S. Taourit, F. Launay, A. Shum Cheong Sing, A. Proust, H. Gérard, et R. Villanneau, « Selective Formation of Epoxylimonene Catalyzed by Phosphonyl/Arsonyl Derivatives of Trivacant Polyoxotungstates at Low Temperature », European Journal of Inorganic Chemistry, vol. 2020, nᵒ 7, p. 605-612, févr. 2020.
    Résumé : The catalytic performances of three organophosphonyl/arsonyl derivatives of POMs were evaluated for the epoxidation of limonene in acetonitrile, using aqueous H2O2 as the oxidant. All three W-based POMs catalysts operated without any additional transition-metal ions and displayed excellent conversion for limonene at temperatures varying from 4 to 50 °C. Furthermore, the use of B,α-[NaHAsW9O33{P(O)R}2]3? (R = tBu, -CH2CH2CO2H) complexes led to the complete conversion of limonene to epoxylimonene at 4 °C. The selectivity of the reaction was modulated by varying the reaction solvent, and it was found that allylic reactions were favored in ethanol. The effect of the catalyst protonation was also investigated by DFT calculations, highlighting the role of protons in the epoxidation process.
    Mots-clés : E-POM, Epoxidation, Homogeneous catalysis, Hybrids, Limonene, POLE 2, Polyoxometalates, Renewable resources.
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  • S. Nasri, M. Hajji, M. Guergueb, S. Dhifaoui, V. Marvaud, F. Loiseau, F. Molton, T. Roisnel, T. Guerfel, et H. Nasri, « Spectroscopic, Electrochemical, Magnetic and Structural Characterization of an Hexamethylenetetramine Co(II) Porphyrin Complex – Application in the Catalytic Degradation of Vat Yellow 1 dye », Journal of Molecular Structure, p. 129676, nov. 2020.
    Résumé : In this study, a new cobaltous-(hexamethylenetetramine) [meso-tetra(para-methoxyphenyl)porphyrin complex with the formula [CoII(TMPP)(HMTA)] (I) was synthesized. The molecular structure was confirmed in solution by 1H NMR spectroscopy and mass spectrometry methods, and the single crystal X-ray diffraction structure of (I) was determined at both room temperature and low temperature. This species was further characterized by infrared, UV-visible and fluorescence spectroscopies, magnetic susceptibility measurements and cyclic voltammetry. The chemical reactivity behavior was also assessed theoretically through Density Functional Theory (DFT) approach. Magnetic investigation indicates that the Co(II)-HMTA porphyrin (I) species at low temperature is a cobaltous low-spin (S = 1/2) species while at high temperature complex (I) exhibits a spin-crossover low-spin (S = 1/2) ↔ high-spin (S = 3/2). The adsorption kinetic of the “vat yellow 1 dye” was carried out in aqueous solution at pH = 6. The experimental results are better fitted using the pseudo second order model. Furthermore, complex (I) was tested as catalyst in the degradation of the vat yellow 1 dye using an aqueous H2O2 solution and by photodegradation under solar light.
    Mots-clés : E-POM, POLE 2.
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  • X. Qi, S. Pillet, C. Graaf, M. Magott, E. ‐E. Bendeif, P. Guionneau, M. Rouzières, V. Marvaud, O. Stefańczyk, D. Pinkowicz, et C. Mathonière, « Photoinduced Mo−CN Bond Breakage in Octacyanomolybdate Leading to Spin Triplet Trapping », Angewandte Chemie International Edition, vol. 59, nᵒ 8, p. 3117-3121, févr. 2020.


  • M. A. Rahman, S. - X. Guo, M. Laurans, G. Izzet, A. Proust, A. M. Bond, et J. Zhang, « Thermodynamics, Electrode Kinetics, and Mechanistic Nuances Associated with the Voltammetric Reduction of Dissolved [n-Bu4N]4[PW11O39{Sn(C6H4)C≡C(C6H4)(N3C4H10)}] and a Surface-Confined Diazonium Derivative », ACS Applied Energy Materials, vol. 3, nᵒ 4, p. 3991-4006, avr. 2020.
    Résumé : The power of Fourier-transformed large amplitude alternating current voltammetry (FTACV) has been applied to parameterize the reduction of the phosphotungstate [PW11O39{Sn(C6H4)C≡C(C6H4)(N3C4H10)}]4– polyoxometalate (POM) (KWSn[N3C4H10]4–/5–/6– processes) at glassy carbon (GC), gold (Au), and platinum (Pt) electrodes as well as its GC surface-confined KWSn[−]4–-grafted diazonium derivative in acetonitrile (0.10 M [n-Bu4N][PF6]). The thermodynamics (E0) and heterogeneous electron-transfer kinetics (k0 and α) were estimated using the Butler–Volmer relationship. FTACV provides access to significantly more detailed mechanistic information related to nonconformance to the theory than widely used DC voltammetric methods, especially with the more intricate surface-confined electrochemistry. Parameterization, the level of agreement, and systematic variations between experimental and simulated data were established by both an experimenter-controlled heuristic method and by a computationally efficient data optimization approach that employed parameter space searches restricted in scope by knowledge of the heuristically based estimations. The first electron transfer process for both acetonitrile-soluble KWSn[N3C4H10]4– and surface-confined KWSn[−]4– is always significantly faster than the second. The electrode dependence order is kGC0 > kAu0 > kPt0 for the KWSn[N3C4H10]4–/5– process. The relatively slower electrode kinetics found for reduction of KWSn[N3C4H10]4– as compared to some other monomeric Keggin POMs may be due to the long organic chain hindering the approach of the POM to the electrode surface, although differences in ion-pairing and other factors also may play a role. Subtle, but systematic, differences identified in comparisons of experimental and simulated voltammetry give rise to apparently data analysis method dependent parameterization and are discussed in terms of nuances not accommodated in the modeling. In the solution-phase voltammetry, data obtained by an electrochemical quartz crystal microbalance and other techniques are consistent with solid adhering to and modifying the electrode surface following reduction of KWSn[N3C4H10]4– to KWSn[N3C4H10]5–. Kinetic and thermodynamic dispersions present in the heterogeneous KWSn[−]4–-grafted electrode are probable causes of nonideality detected in the surface-confined voltammetry of this material. Thus, FTACV gives valuable insights into what is needed to provide a more realistic description of the polyoxometalate/electrode interface in polyoxometalate electrochemistry by revealing subtle nuances that are often overlooked.
    Mots-clés : E-POM, POLE 2.
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  • R. Salles, B. Abécassis, E. Derat, D. Brouri, A. Bernard, Q. Zhang, A. Proust, C. Desmarets, et G. Izzet, « Hierarchical Self-Assembly of Polyoxometalate-Based Organo Palladium(II) Metallomacrocycles via Electrostatic Interactions », Inorganic Chemistry, vol. 59, nᵒ 4, p. 2458-2463, févr. 2020.
    Résumé : The design and synthesis of a supramolecular square composed of polyoxometalate-based hybrid donors and ethylenediamine palladium(II) nodes are reported. The structure of the metallomacrocycle scaffold was inferred by diffusion NMR, small-angle X-ray scattering (SAXS), and molecular modeling. The metallomacrocycle scaffold that contains negatively and positively charged subunits can further self-assemble owing to a competition between the solvation energy of the discrete species and intermolecular electrostatic interactions. When the dissociating character of the solvent was lowered or when in the presence of a protic solvent, different types of multiscale organizations (vesicles and pseudo-1D structures) were selectively formed and were characterized by SAXS and transmission electron microscopy.
    Mots-clés : ARC, E-POM, MACO, POLE 1, POLE 2.
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  • M. Sellin, V. Marvaud, et M. Malischewski, « Isolation and Structural Characterization of Eightfold Protonated Octacyanometalates [M(CNH) <sub>8</sub> ] <sup>4+</sup> (M=Mo <sup>IV</sup> , W <sup>IV</sup> ) from Superacids », Angewandte Chemie International Edition, vol. 59, nᵒ 26, p. 10519-10522, juin 2020.


  • A. Solé-Daura, T. Zhang, H. Fouilloux, C. Robert, C. M. Thomas, L. - M. Chamoreau, J. J. Carbó, A. Proust, G. Guillemot, et J. M. Poblet, « Catalyst Design for Alkene Epoxidation by Molecular Analogues of Heterogeneous Titanium-Silicalite Catalysts », ACS Catalysis, vol. 10, nᵒ 8, p. 4737-4750, avr. 2020.
    Résumé : The epoxidation of allylic alcohols with H2O2 catalyzed by the hybrid [α-B-SbW9O33(tBuSiO)3Ti(OiPr)]3– (1) anion as a molecular model of heterogeneous Ti-silicalite TS-1 catalyst was analyzed by means of DFT to determine the main factors that control the catalytic process and, finally, to improve the value of the available catalysts. Our calculations revealed that unlike other alkenes, allylic alcohols can bind the Ti center after activation of the precatalyst via hydrolysis to give the corresponding Ti-alcoholate, which is the catalyst resting state. Next, the dissociative addition of hydrogen peroxide to Ti causes the cleavage of a Ti–OSi junction to form a Ti(η2-OOH) moiety. The partial detachment of the Ti from the catalyst structure yields an intermediate with a flexible Ti center from which the Ti-OOH group can transfer an electrophilic oxygen to the alkene substrate in an inner-sphere fashion. The rate-determining process, which involves the heterolytic activation of H2O2 over the Ti(IV) and the electrophilic O-transfer, accounts for an overall free-energy barrier of 23.0 kcal mol–1 for 2-methyl-2-buten-1-ol, in line with the experimental value of 22.3. Conversely, the outer-sphere O-transfer—also accessible to nonfunctionalized alkenes—occurs through a more strained transition state that lays above in energy (by ∼4 kcal mol–1), giving a clue to explain the low yields reported experimentally for nonfunctionalized olefins. We also found that reducing the bulkiness of the substituents in the silanol functions of the catalyst has a positive influence on the catalytic activity, decreasing the overall free-energy barriers for the outer-sphere path. With this knowledge, we developed other catalytic species with tailored steric properties based on [SbW9O33(RSiOH)3]3– structure (R =iPr and nPr), which were synthesized, characterized, and successfully applied to the catalytic epoxidation of unfunctionalized alkenes. Present results clearly show that the detailed knowledge of the reaction mechanisms, even for complex processes, is possible nowadays and that the acquired information allows designing catalysts with desired activities.
    Mots-clés : E-POM, POLE 2.
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2019



  • Q. Arnoux, C. Blouzon, D. Li, Y. J. Dappe, A. Smogunov, P. Bonville, L. Tortech, et J. - B. Moussy, « Controlling the magnetic exchange coupling in hybrid heterojunctions via spacer layers of π-conjugated molecules », Physical Review B, vol. 99, nᵒ 14, p. 144405, avr. 2019.
    Résumé : Mastering and understanding the magnetic couplings between magnetic electrodes separated by organic layers are crucial for developing new hybrid spintronic devices. We study the magnetic exchange interactions in organic-inorganic heterojunctions and unveil the possibility of controlling the strength of the magnetic exchange coupling between two ferromagnetic electrodes across π-conjugated molecules’ (α-sexithiophene or para-sexiphenyl) ultrathin film. In Fe3O4/π-conjugated molecules/Co magnetic tunnel junctions, an antiferromagnetic interlayer exchange coupling with variable strength is observed according to the nature of the aromatic rings (thiophene or phenyl groups). The underlying physical mechanism is revealed by ab initio calculations relating the strength of magnetic coupling to the spin moment penetration into a molecular layer at the molecule/Co interface. The prospect that magnetic coupling between two ferromagnetic electrodes can be mediated and tuned by organic molecules opens different perspectives in the way magnetization of organic tunnel junctions or spin valves can be driven.
    Mots-clés : E-POM, POLE 2.
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  • L. Ben Haj Hassen, S. Dhifaoui, Y. Rousselin, V. Marvaud, C. Stern, C. E. Schulz, et H. Nasri, « New insights on the electronic, magnetic, electric and molecular structure of a bis-(4-cyanopyridine) iron(III) complex with the meso-tetrakis(4-methoxyphenyl)porphyrin », Inorganica Chimica Acta, vol. 486, p. 675-683, févr. 2019.
    Résumé : We have successfully synthesized and characterized a new low-spin iron(III) bis(4-cyanopyridine) complex with a meso-porphyrin substituted in the para positions of the phenyls by the methoxy group, namely the bis(4-cyanopyridine)[(meso-tetrakis(4-metoxyphenylporphyrinato)]iron(III) trifluoromethanesulfonate chlorobenzene monosolvate complex with the formula [FeIII(TMPP)(4-CNpy)2]SO3CF3.C6H5Cl (I). This species was characterized through ultraviolet–visible, Fourier-transform infrared and Mössbauer spectroscopy as well as by SQUID magnetometry, cyclic voltammetry, and X-ray crystallography. These characterizations indicated that our synthetic heme model is a low-spin (S = 1/2) coordination compound and especially shows that the structural, electronic and the magnetic properties of complex (I) are closely dominated by the presence of the methoxy σ-donor group at the para positions of the meso-porphyrin.
    Mots-clés : Cyclic voltammetry, E-POM, Iron(III) porphyrin, Magnetic properties, POLE 2, X-ray Molecular structure.
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  • R. Breitwieser, A. Garnier, T. Auvray, A. - T. Ngo, B. Baptiste, N. Menguy, A. Proust, C. Petit, F. Volatron, et C. Salzemann, « Protective Effect of Polyoxometalates in {Mo132}/Maghemite Binary Superlattices Under Annealing », Frontiers in Chemistry, vol. 7, 2019.
    Résumé : The binary assembly DDA-{Mo132} / OA-γ-Fe2O3 (DDA=didodecyldimethylammonium, {Mo132}=[Mo132O372(CH3COO)30(H2O)72]42-, OA = oleic acid) constitutes one of the two examples in the literature of binary superlattices made of a mixing of nanocrystals and oxo-clusters. In a precedent work, we reported in details the preparation of such magnetic binary systems and studied the effect of the nature of the polyoxometalates (POMs) on the magnetic properties. In the present paper, we study the stability of this model binary assembly under heating at various temperatures. Indeed, especially if magnetic and/or transport properties are targeted, an annealing can be essential to change the phase of the nanocrystals in a more magnetic one and/or to desorb the organic capping of the nano-objects that can constitute an obstacle to the electronic communication between the nano-objects. The binary assembly showed a good stability at temperatures until around 400°C under vacuum thanks to the presence of the POMs that permits to avoid the aggregation of the nanocrystals as well as preserve their periodical arrangement. On the contrary, an assembly made of pure γ-Fe2O3 nanocrystals displays a clear aggregation of the nano-objects from 370°C, as attested by transmission and scanning electronic microscopies and confirmed by magnetic measurements. The stability of such POMs/nanocrystals assemblies opens the way to (i) the elaboration of new binary assemblies from POMs and numerous kinds of nanocrystals with a good control on the magnetic properties and to (ii) the investigation of new physical properties as exchange coupling, or magneto-transport in such systems.
    Mots-clés : annealing, binary superlattices, E-POM, Maghemite, magnetism, POLE 2, Polyoxometalate.
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  • K. D. Francesca, S. Lenfant, M. Laurans, F. Volatron, G. Izzet, V. Humblot, C. Methivier, D. Guerin, A. Proust, et D. Vuillaume, « Charge transport through redox active [H7P8W48O184]33− polyoxometalates self-assembled onto gold surfaces and gold nanodots », Nanoscale, vol. 11, nᵒ 4, p. 1863-1878, janv. 2019.
    Résumé : Polyoxometalates (POMs) are redox-active molecular oxides, which attract growing interest for their integration into nano-devices, such as high-density data storage non-volatile memories. In this work, we investigated the electrostatic deposition of the negatively charged [H7P8W48O184]33− POM onto positively charged 8-amino-1-octanethiol self-assembled monolayers (SAMs) preformed onto gold substrates or onto an array of gold nanodots. The ring-shaped [H7P8W48O184]33− POM was selected as an example of large POMs with high charge storage capacity. To avoid the formation of POM aggregates onto the substrates, which would introduce variability in the local electrical properties, special attention has to be paid to the preformed SAM seeding layer, which should itself be deprived of aggregates. Where necessary, rinsing steps were found to be crucial to eliminate these aggregates and to provide uniformly covered substrates for subsequent POM deposition and electrical characterizations. This especially holds for commercially available gold/glass substrates while these rinsing steps were not essential in the case of template stripped gold of very low roughness. Charge transport through the related molecular junctions and nanodot molecule junctions (NMJs) has been probed by conducting-AFM. We analyzed the current–voltage curves with different models: electron tunneling though the SAMs (Simmons model), transition voltage spectroscopy (TVS) method or molecular single energy level mediated transport (Landauer equation) and we discussed the energetics of the molecular junctions. We concluded to an energy level alignment of the alkyl spacer and POM lowest occupied molecular orbitals (LUMOs), probably due to dipolar effects.
    Mots-clés : E-POM, POLE 2.
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  • P. Galiyeva, H. Alem, H. Rinnert, L. Balan, S. Blanchard, G. Medjahdi, B. Uralbekov, et R. Schneider, « Highly fluorescent, color tunable and magnetic quaternary Ag–In–Mn–Zn–S quantum dots », Inorganic Chemistry Frontiers, vol. 6, nᵒ 6, p. 1422-1431, juin 2019.
    Résumé : Mn-Doped quantum dots (QDs) are of high interest for numerous applications like solar cells, optoelectronics, optosensing, or bioimaging. Here, we report the preparation of quaternary (AgInS2)x(MnS)y(ZnS)1−x−y QDs, thereafter noted Mn : AIZS via a thermally induced decomposition of Ag, In, Zn and Mn precursors in the presence of oleylamine and dodecanethiol. The Mn : AIZS QDs have an average diameter of 3.5 nm and their XRD patterns can be indexed with the orthorhombic phase of AgInS2. The incorporation of Mn2+ ions in the AIZS crystal lattice results in a red-shift of the photoluminescence (PL) emission maximum depending on the Mn2+ content. The PL quantum yields decrease upon loading with Mn2+ but remained high (53–31%) until 50% theoretical loading in Mn2+. Steady state, PL excitation and time-resolved PL measurements suggest that Mn2+-dependent trap states are involved in the PL emission. Mn : AIZS QDs exhibit also magnetic properties. In addition, Mn : AIZS QDs can easily be transferred to the aqueous phase using the PMAO amphiphilic polymer without alteration of their optical properties (PL quantum yield up to 51%), revealing their high potential for biological applications.
    Mots-clés : E-POM, POLE 2.
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  • M. Girardi, D. Platzer, S. Griveau, F. Bedioui, S. Alves, A. Proust, et S. Blanchard, « Assessing the Electrocatalytic Properties of the Cp*RhIII2+-Polyoxometalate Derivative [H2PW11O39RhIIICp*(OH2)]3– towards CO2 Reduction », European Journal of Inorganic Chemistry, vol. 2019, nᵒ 3-4, p. 387-393, 2019.
    Résumé : Storage of electricity produced intermittently by renewable energy sources is a societal issue. Besides the use of batteries and supercapacitors, conversion of excess electricity into chemical energy is also actively investigated. The conversion of CO2 to fuel or fuel precursors is an option that requires the use of a catalyst to overcome the high activation energy barrier. Of molecular catalysts, metal complexes with polypyridyl ligands are well represented, among which the [Cp*Rh(bpy)Cl]+ and [M(bpy)(CO)3X] (M = Re, Mn) complexes. As redox non-innocent ligand, the bipyridine ligand is generally involved in the reduction mechanisms. It is thus tempting to replace it by other redox non-innocent ligands such as vacant polyoxometalates (POMs). We have thus prepared [α-H2PW11O39RhIIICp*(OH2)]3– which is closely related to [Cp*RhIII(bpy)Cl]+ by substitution of the monovacant [PW11O39]7– Keggin-type POM for the bipyridine ligand. Its activity towards CO2 reduction has been assessed in acetonitrile in the presence of water. Compared to [Cp*Rh(bpy)Cl]+ that produces formate selectively over CO and H2, the POM derived catalyst favors proton reduction over CO2 reduction.
    Mots-clés : Carbon dioxide fixation, CSOB, E-POM, Non-innocent ligands, POLE 2, POLE 3, Polyoxometalates, Redox chemistry.
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  • O. Makrygenni, F. L. Bentaleb, D. Brouri, A. Proust, F. Launay, et R. Villanneau, « Selective uptake of La3+ ions with polyoxometalates-functionalized mesoporous SBA-15: An EXAFS study », Microporous and Mesoporous Materials, vol. 287, p. 264-270, oct. 2019.
    Résumé : In this work, mesoporous materials based on inorganic/organic polyoxometalate (POMs) hybrids with the ability of further incorporating heterometallic lanthanum cations were designed. On the basis of the La3+ coordination to vacant organophosphonyle derivatives of POMs previously studied, herein POMs-grafted onto an amino-functionalized mesoporous SBA-15 ({NH2}-SBA-15) with incorporated La3+ ions were synthesized by varying the amounts of the latter. LIII-edge La EXAFS spectroscopy of the resulting materials provided local structural information around LaIII ions (i.e. number, nature and distances of neighboring atoms), which are comparable to that of the LaIII complexes of POMs hybrids. This technique, in addition with 31P CP-MAS NMR spectroscopy, gave definitive clues for a selective uptake of the incorporated La3+ ions by the POMs grafted onto the {NH2}-SBA-15 supports. This study is a clear demonstration that, due to their chelate effect, POMs hybrids act as efficient ligands for La3+ even in the presence of competitive adsorption sites. Consequently, a regular distribution of the La3+ ions along the channels of the SBA-15 is thus observed in these materials due to the nanostructuration of the POMs onto the support.
    Mots-clés : E-POM, EXAFS, Lanthanum, Mesoporous silica, POLE 2, Polyoxometalates.
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  • O. Makrygenni, D. Brouri, A. Proust, F. Launay, et R. Villanneau, « Immobilization of polyoxometalate hybrid catalysts onto mesoporous silica supports using phenylene diisothiocyanate as a cross-linking agent », Microporous and Mesoporous Materials, vol. 278, p. 314-321, avr. 2019.
    Résumé : The hybrid derivative of heteropolytungstate bearing two aniline groups, namely (nBu4N)3[NaHPW9O34{As(O)C6H4NH2}2], was post-functionalized in the presence of 1,4-phenylene diisothiocyanate (PDITC). The resulting molecular moiety was characterized by IR, 1H and 31P NMR spectroscopy. In a second step, this post-functionalized hybrid of polyoxometalate was covalently grafted onto the surface of an amino-functionalized SBA-15 silica by means of the formation of thiourea bonds. This simple and efficient strategy of immobilization did not require the use of a coupling agent and was performed in mild reaction conditions. Various physicochemical techniques (13C and 31P CPMAS NMR spectroscopies, XPS, XRF, HR-TEM microscopy and N2 sorption) contributed to the full characterization of the supported catalyst. In addition HR-TEM was found to be an essential technique for the identification of the polyoxometalate units inside the pores of SBA-15. Finally, the catalytic performances of the supported polyoxometalates were evaluated in the epoxidation of cyclooctene with aqueous H2O2 in acetonitrile at 50 °C.
    Mots-clés : Anchored homogeneous catalysts, E-POM, Epoxidation catalysis, Functionalized mesoporous silica materials, POLE 2, Polyoxometalate hybrids.
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  • J. Qu, C. Livache, B. Martinez, C. Gréboval, A. Chu, E. Meriggio, J. Ramade, H. Cruguel, X. Z. Xu, A. Proust, F. Volatron, G. Cabailh, N. Goubet, et E. Lhuillier, « Transport in ITO Nanocrystals with Short- to Long-Wave Infrared Absorption for Heavy-Metal-Free Infrared Photodetection », ACS Applied Nano Materials, vol. 2, nᵒ 3, p. 1621-1630, mars 2019.
    Résumé : Nanocrystals are often described as interesting materials for the design of low-cost optoelectronic devices, especially in the infrared range. However, the driving materials reaching infrared absorption generally contain heavy metals (Pb and Hg) with a high toxicity. An alternative strategy to achieve infrared transition is the use of doped semiconductors presenting intraband or plasmonic transition in the short-, mid-, and long-wave infrared. This strategy may offer more flexibility regarding the range of possible candidate materials. In particular, significant progress has been achieved for the synthesis of doped oxides and for the control of their doping magnitude. Among them, tin doped indium oxide (ITO) is the one providing the broadest spectral tunability. Here we test the potential of such ITO nanoparticles for photoconduction in the infrared. We demonstrate that In2O3 nanoparticles present an intraband absorption in the mid-infrared range which is transformed into a plasmonic feature as doping is introduced. We have determined the cross section associated with the plasmonic transition to be in the 1–3 × 10–13 cm2 range. We have observed that the nanocrystals can be made conductive and photoconductive thanks to a ligand exchange using a short carboxylic acid, leading to a dark conduction with n-type character. We present evidence that the observed photoresponse in the infrared is the result of a bolometric effect.
    Mots-clés : E-POM, POLE 2.
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  • M. Rupp, T. Auvray, E. Rousset, G. M. Mercier, V. Marvaud, D. G. Kurth, et G. S. Hanan, « Photocatalytic Hydrogen Evolution Driven by a Heteroleptic Ruthenium(II) Bis(terpyridine) Complex », Inorganic Chemistry, vol. 58, nᵒ 14, p. 9127-9134, juill. 2019.
    Résumé : Since the initial report by Lehn et al. in 1979, ruthenium tris(bipyridine) ([Ru(bpy)3]2+) and its numerous derivatives were applied as photosensitizers (PSs) in a large panel of photocatalytic conditions while the bis(terpyridine) analogues were disregarded because of their low quantum yields and short excited-state lifetimes. In this study, we prepared a new terpyridine ligand, 4′-(4-bromophenyl)-4,4‴:4″,4‴′-dipyridinyl- 2,2′:6′,2″-terpyridine (Bipytpy) and used it to prepare the heteroleptic complex [Ru(Tolyltpy)(Bipytpy)](PF6)2 (1; Tolyltpy = 4′-tolyl-2,2′:6′,2′-terpyridine). Complex 1 exhibits enhanced photophysical properties with a higher quantum yield (7.4 × 10–4) and a longer excited-state lifetime (3.8 ns) compared to those of [Ru(Tolyltpy)2](PF6)2 (3 × 10–5 and 0.74 ns, respectively). These enhanced photophysical characteristics and the potential for PS–catalyst interaction through the peripheral pyridines led us to apply the complex for visible-light-driven hydrogen evolution. The photocatalytic system based on 1 as the PS, triethanolamine as a sacrificial donor, and cobaloxime as a catalyst exhibits sustained activity over more than 10 days under blue-light irradiation (light-emitting diode centered at 450 nm). A maximum turnover number of 764 was obtained after 12 days.
    Mots-clés : E-POM, POLE 2.
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  • Z. Zhao, N. Barrett, Q. Wu, D. Martinotti, L. Tortech, R. Haumont, M. Pellen, et E. K. H. Salje, « Interaction of low-energy electrons with surface polarity near ferroelastic domain boundaries », Physical Review Materials, vol. 3, nᵒ 4, p. 043601, avr. 2019.
    Résumé : We derive surface polarity at and near ferroelastic domain boundaries from molecular dynamics simulations based on an ionic spring model. Interatomic gradient forces lead to flexoelectricity which, in turn, generates polarity at the surface and in twin boundaries. We then derive generic properties of electron scattering spectra equivalent to those observed in low-energy electron microscopy (LEEM) and mirror electron microscopy (MEM) experiments. Negatively (positively) charged surfaces reflect (attract) incident electrons with low kinetic energy. The electron images reveal the valley and ridge surface structures near the intersection of the twin boundary and the surface. Polarity in surface layers is predicted to be visible in LEEM and MEM spectra at neutral surfaces, but much less when surfaces are charged. Inward polarity reflects electrons similar to negative surface charges, and outward polarity backscatters electrons like positive surface charges. Both the polarity in the twin boundary and the physical topography scatter electrons, consistent with experimental LEEM and MEM experiments on CaTiO3 with (001) and (111) surface terminations.
    Mots-clés : E-POM, POLE 2.
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  • Q. Zhu, B. Paci, A. Generosi, S. Renaudineau, P. Gouzerh, X. Liang, C. Mathieu, C. Rountree, G. Izzet, A. Proust, N. Barrett, et L. Tortech, « Conductivity via Thermally Induced Gap States in a Polyoxometalate Thin Layer », The Journal of Physical Chemistry C, vol. 123, nᵒ 3, p. 1922-1930, janv. 2019.

2018



  • F. A. Black, A. Jacquart, G. Toupalas, S. Alves, A. Proust, I. P. Clark, E. A. Gibson, et G. Izzet, « Rapid photoinduced charge injection into covalent polyoxometalate–bodipy conjugates », Chemical Science, vol. 9, nᵒ 25, p. 5578-5584, 2018.
    Mots-clés : CSOB, E-POM, POLE 2, POLE 3.
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  • N. Bridonneau, P. Quatremare, H. J. von Bardeleben, J. - L. Cantin, S. Pillet, E. - E. Bendeif, et V. Marvaud, « Direct Evidence of a Photoinduced Electron Transfer in Diluted “Molybdenum-Copper” Molecular Compounds », European Journal of Inorganic Chemistry, vol. 2018, nᵒ 3-4, p. 370-377, janv. 2018.
    Résumé : For the first time, direct evidence of a photoinduced intramolecular electron transfer has been found in the “molybdenum-copper“ family of cyanide complexes that corresponds to a [MoIV–CuII]→[MoV–CuI] transition. The design and synthesis of a diluted molecular system, [Mo(Zn(1–x)Cux)2-tren] (x = 0, ε, 1, 5 and 10 %, , with ε corresponding to ppm ratio), viewed as new model compounds, have allowed good characterization of the metastable states involved in the process and provided evidence for two different mechanisms. By using squid magnetometry, EPR spectroscopy and X-ray diffraction, the results of this study have confirmed not only the photoinduced electron transfer, but also supports the light-induced excited spin state trapping effect centred on the molybdenum, thought to be due to the presence of a high-spin state (S = 1). This article provides a better understanding of the photomagnetic behaviour in Mo-Cu complexes and reveals the importance of orbital overlap to differentiate the two effects.
    Mots-clés : copper, E-POM, Electron transfer, Magentic properties, Molybdenum, Photomagnetism, POLE 2, Spin transition.
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  • T. Buchecker, P. Schmid, S. Renaudineau, O. Diat, A. Proust, A. Pfitzner, et P. Bauduin, « Polyoxometalates in the Hofmeister series », Chemical Communications, vol. 54, nᵒ 15, p. 1833-1836, févr. 2018.
    Résumé : We propose a simple experimental procedure based on the cloud point measurement of a non-ionic surfactant as a tool for (i) estimating the super-chaotropic behaviour of polyoxometalates (POMs) and for (ii) establishing a classification of POMs according to their affinity towards polar surfaces.
    Mots-clés : E-POM.
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  • S. Dhifaoui, C. Mchiri, P. Quatremare, V. Marvaud, A. Bujacz, et H. Nasri, « Molecular structure, magnetic properties, cyclic voltammetry of the low-spin iron(III) Bis(4-ethylaniline) complex with the para-chloro substituted meso-tetraphenylporphyrin », Journal of Molecular Structure, vol. 1153, p. 353-359, févr. 2018.
    Résumé : In this study, the preparation of a new iron(III) hexacoordinated metalloporphyrin namely the bis(4-ethylaniline){meso-tetra(para-chlorophenyl)porphyrinato}iron(III) triflate hemi-4-ethylaniline monohydrate with the formula [FeIII(TClPP)(PhEtNH2)2]SO3CF3•1/2PhEtNH2•H2O (I) was reported. This is the first example of an iron(III) metalloporphyrin bis(primary amine) with an aryl group adjacent to the amino group. This species was characterized by elemental, spectroscopic analysis including UV–visible and IR data, cyclic voltammetry, SQUID measurements and X-ray molecular structure. The mean equatorial distance between the iron(III) and the nitrogens of the porphyrin is appropriate for a low-spin (S = 1/2) iron(III) porphyrin complex. The magnetic data confirm the low-spin state of our ferric derivative while the cyclic voltammetry indicates a shift of the half potential E1/2[Fe(III)/Fe(II)] of complex (I) toward more negative value. In the crystal of (I), the [FeIII(TClPP)(PhEtNH2)2]+ ions, the triflate counterions and the water molecules are involved in a number of O__H⋯O, N__H⋯O, C–H⋯O and C__H⋯π intermolecular interactions forming a three-dimension network.
    Mots-clés : E-POM, Iron(III) porphyrins, Magnetic data, POLE 2, UV–Visible, X-ray molecular structure.
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  • S. Dhifaoui, S. Nasri, G. Gontard, A. C. Ghosh, Y. Garcia, C. Bonifàcio, S. Najmudin, V. Marvaud, et H. Nasri, « Synthesis, Mössbauer, cyclic voltammetry, magnetic properties and molecular structures of the low-spin iron(III) bis(pyrazine) complexes with the para-fluoro and para-chloro substituted meso-tetraphenylporphyrin », Inorganica Chimica Acta, vol. 477, p. 114-121, mai 2018.
    Résumé : Two new bis(pyrazine) iron(III) meso-porphyrin complexes are reported here: the bis(pyrazine)[5,10,15,20-tetra(para-fluoro-phenyl)porphyrinato]iron(III) triflate; [Fe(TFPP)(pyz)2]SO3CF3 (1) and the bis(pyrazine)[5,10,15,20-tetra(para-chlorophenyl)porphyrinato]iron(III) triflate; [Fe(TClPP)(pyz)2]SO3CF3 (2). The X-ray molecular structures of 1–2 show that the planes of the two pyrazine axial ligands are perpendicular and that the porphyrin macrocycles of these derivatives are very distorted, leading to a short average equatorial iron-pyrrole N atoms distance appropriate for low-spin ferric porphyrinates. The Mössbauer data of 1–2 feature relatively low values of the quadrupole splitting (ΔEQ ∼ 1.20 mm.s−1) appropriate for low-spin Fe(III) metalloporphyrin with perpendicular orientation of N-donor planar ligands. The temperature dependence of the magnetic susceptibility and the magnetization curves have shown that the results for complexes 1–2 confirm the low-spin state of our two-ferric species, while the cyclic voltammetry data show that the half potential [Fe(III)/Fe(II)] values are shifted anodically compared to the β-pyrrole substituted porphyrin octaethylporphyrin with parallel bis(N-donor) planar axial ligands.
    Mots-clés : E-POM, Iron(III) porphyrins, Magnetic properties, Mössbauer, POLE 2, UV-visible, X-ray molecular structure.
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  • B. Doistau, L. Benda, B. Hasenknopf, V. Marvaud, et G. Vives, « Switching Magnetic Properties by a Mechanical Motion », Magnetochemistry, vol. 4, nᵒ 1, p. 5, mars 2018.
    Résumé : Switching magnetic properties have attracted a wide interest from inorganic chemist for the objectives of information storage and quantum computing at the molecular level. This review is focused on magnetic switches based on a mechanical motion, which is an innovative approach. Three main strategies to control magnetic properties by a mechanical motion have been developed in the literature and will be described. The first one (ligand-induced spin change) consists in modulating the ligand field strength by a configuration change of the ligand in spin-crossover complexes. The second one (coordination-induced spin-state switching) is based on a change in the coordination number of a metallic center that is triggered by the motion of one ligand. The third one uses the modulation of the exchange interaction between two spin-centers by a mechanical motion.
    Mots-clés : E-POM, GOBS, LD-CISSS, LD-LISC, magnetism, molecular machine, molecular switch, photoisomerization, POLE 2, POLE 3, spin crossover.
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  • S. Hupin, H. Lavanant, S. Renaudineau, A. Pr

    oust, G. Izzet, M. Groessl, et C. Afonso, « A calibration framework for the determination of accurate collision cross sections of polyanions using polyoxometalate standards », Rapid Communications in Mass Spectrometry, vol. 32, nᵒ 19, p. 1703-1710, 2018.
    Résumé : Rationale Polyoxometalates (POMs) are remarkable oxo-clusters forming compact highly charged anions. We measured their collision cross sections (CCS) in N2 with drift tube ion mobility spectrometry (DTIMS). These values were then used to calibrate a traveling wave ion mobility spectrometry (TWIMS) device and the accuracy of the calibration was tested. Methods Six POM standards were analyzed by DTIM-MS (Tofwerk, Thun, Switzerland) at different voltages to determine absolute DTCCS (N2) values. Five POM compounds (Lindqvist TBA2Mo6O19; decatungstate TBA4W10O32; Keggin TBA3PMo12O40; TBA3PW12O40 and Dawson TBA6P2W18O62) were used for the calibration of the TWIM-MS instrument (Synapt G2 HDMS, Waters, Manchester, UK) and a sixth Dawson POM, TBA9P2Nb3W15O62, was used to compare the accuracy of the calibrations with POM or with polyalanine and dextran reference ions. Results We determined 45 DTCCS (N2) values at 30°C or 60°C. Fourteen DTCCS (N2) values at 30°C were used to perform calibration of the TWIMS instrument. Better correlations were observed than when DTCCS values in helium from the literature were used. The accuracy tests on six ions of Dawson POM TBA9P2Nb3W15O62 led to relative errors below 3.1% while relative errors of 3.6% to 10.1% were observed when calibration was performed with polyalanine and dextran reference ions. Conclusions Our novel calibration strategy for determination of CCS values of multiply negatively charged ions on TWIM-MS devices based on DTCCS (N2) of standard POM structures covered a wider range of CCS and improved the accuracy to 2.1% relative error on average compared with 6.9% using polyalanine and dextran calibration.
    Mots-clés : E-POM.
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  • M. Laurans, K. D. Francesca, F. Volatron, G. Izzet, D. Guerin, D. Vuillaume, S. Lenfant, et A. Proust, « Molecular signature of polyoxometalates in electron transport of silicon-based molecular junctions », Nanoscale, vol. 10, nᵒ 36, p. 17156-17165, sept. 2018.
    Résumé : Polyoxometalates (POMs) are unconventional electro-active molecules with a great potential for applications in molecular memories, providing efficient processing steps onto electrodes are available. The synthesis of the organic–inorganic polyoxometalate hybrids [PM11O39{Sn(C6H4)CC(C6H4)N2}]3− (M = Mo, W) endowed with a remote diazonium function is reported together with their covalent immobilization onto hydrogenated n-Si(100) substrates. Electron transport measurements through the resulting densely-packed monolayers contacted with a mercury drop as a top electrode confirms their homogeneity. Adjustment of the current–voltage curves with the Simmon's equation gives a mean tunnel energy barrier ΦPOM of 1.8 eV and 1.6 eV, for the Silicon–Molecules–Metal (SMM) junctions based on the polyoxotungstates (M = W) and polyoxomolybdates (M = Mo), respectively. This follows the trend observed in the electrochemical properties of POMs in solution, the polyoxomolybdates being easier to reduce than the polyoxotungstates, in agreement with lowest unoccupied molecular orbitals (LUMOs) of lower energy. The molecular signature of the POMs is thus clearly identifiable in the solid-state electrical properties and the unmatched diversity of POM molecular and electronic structures should offer a great modularity.
    Mots-clés : E-POM.
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  • O. Makrygenni, E. Secret, A. Michel, D. Brouri, V. Dupuis, A. Proust, J. - M. Siaugue, et R. Villanneau, « Heteropolytungstate-decorated core-shell magnetic nanoparticles: A covalent strategy for polyoxometalate-based hybrid nanomaterials », Journal of Colloid and Interface Science, vol. 514, p. 49-58, mars 2018.
    Résumé : Amino-functionalized core–shell magnetic nanoparticles have been covalently grafted with Polyoxometalates (POMs). These multifunctional nanocomposites have been obtained through the coupling of heteropolytungstate-based hybrids bearing carboxylic acid functions with aminopropyl functions that decorate the core–shell nanoparticles. The physical properties of the resulting materials have been studied by a large set of techniques. The very good nanostructuration of the POMs at the surface of the obtained nanoparticles have thus been directly observed by high-resolution transmission electronic microscopy (HR-TEM). Furthermore, the hyperthermia properties of these nanocomposites have been also considered as a function of the size of the magnetic core. Finally, the stability of these suspensions in organic media makes them particularly interesting in the frame of their processing or their potential use as nanocatalysts.
    Mots-clés : Core-shell nanoparticles, E-POM, HR-TEM, Hybrid materials, POLE 2, Polyoxometalates.
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  • B. Martinez, C. Livache, E. Meriggio, X. Z. Xu, H. Cruguel, E. Lacaze, A. Proust, S. Ithurria, M. G. Silly, G. Cabailh, F. Volatron, et E. Lhuillier, « Polyoxometalate as Control Agent for the Doping in HgSe Self-Doped Nanocrystals », The Journal of Physical Chemistry C, vol. 122, nᵒ 46, p. 26680-26685, nov. 2018.
    Résumé : Intraband and plasmonic transitions have appeared over the last years as an interesting tool to achieve optical absorption in the mid-infrared. Tuning the doping magnitude has become a major challenge not only to tune the optical spectrum but also properties such as the dark current or the time response. Here, we investigate the case of self-doped HgSe colloidal quantum dots (CQDs). At present, tuning of the doping relies on band bending induced by a dipole design at the nanoparticle surface. With such a surface gating approach, it is difficult to conciliate both massive tuning of the Fermi level and the preservation of transport properties of the CQD arrays. Here, we propose a strategy to graft functionalized polyoxometalates (POMs) at the CQD surface and obtain simultaneously a massive tuning of the carrier density (≈5 electrons per nanoparticle) and conduction properties. We bring a consistent demonstration of the HgSe CQD doping decrease by a charge transfer to the POM. This method is highly promising for large tuning of carrier density in degenerately doped semiconductor nanoparticles.
    Mots-clés : E-POM.
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  • F. Mercier-Bion, J. Li, H. Lotz, L. Tortech, D. Neff, et P. Dillmann, « Electrical properties of iron corrosion layers formed in anoxic environments at the nanometer scale », Corrosion Science, vol. 137, p. 98-110, juin 2018.
    Résumé : The electrical properties of the corrosion layers on archaeological iron artefacts were determined by Conductive Atomic Force Microscopy. Different corrosion products were studied: FeII carbonates, magnetite entrapped in the carbonate, and iron sulfides. The results indicate that the ferrous carbonate matrix is insulating, and that magnetite and iron sulfides have a conductive character, although these phases are not systematically connected to the metal. This suggests that electrons produced by the anodic dissolution of metal would be conducted to the external part of the corrosion product layer through a three-dimensional network of connected magnetite strips passing through the ferrous carbonate matrix.
    Mots-clés : Archaeological artefact, C-AFM, E-POM, Electrical properties, FESEM, Iron corrosion, POLE 2, μRaman.
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  • E. Nikoloudakis, K. Karikis, M. Laurans, C. Kokotidou, A. Solé-Daura, J. J. Carbó, A. Charisiadis, G. Charalambidis, G. Izzet, A. Mitraki, A. M. Douvas, J. M. Poblet, A. Proust, et A. G. Coutsolelos, « Self-assembly study of nanometric spheres from polyoxometalate-phenylalanine hybrids, an experimental and theoretical approach », Dalton Transactions, vol. 47, nᵒ 18, p. 6304-6313, mai 2018.
    Résumé : Herein, we report on the study of supramolecular assemblies based on polyoxometalates (POMs) upon their modification with amino acids. Two POM-amino acid hybrids were synthesized by coupling a functionalized Keggin type polyoxoanion [PW11O39{Sn(C6H4)CC(C6H4)COOH}]4− with carboxyl-protected (methyl-ester) phenylalanine or diphenylalanine peptides. Surprisingly, all compounds, including the initial POM, formed supramolecular nanospheres in different solvent mixtures, which were examined by scanning electron microscopy (SEM). Molecular dynamics (MD) simulations for the POM-amino acid species revealed that the hydrophobic forces are mainly responsible for the initial aggregation into incipient micelle type structures, in which the organic arms are buried inside the aggregate while POM polar heads are more exposed to the solvent with tetrabutyl-ammonium counter cations acting as linkers.
    Mots-clés : E-POM.
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  • M. Piot, B. Abécassis, D. Brouri, C. Troufflard, A. Proust, et G. Izzet, « Control of the hierarchical self-assembly of polyoxometalate-based metallomacrocycles by redox trigger and solvent composition », Proceedings of the National Academy of Sciences, vol. 115, nᵒ 36, p. 8895-8900, sept. 2018.
    Résumé : Discrete metallomacrocycles are attractive scaffolds for the formation of complex supramolecular architectures with emergent properties. We herein describe the formation of hierarchical nanostructures using preformed metallomacrocycles by coordination-driven self-assembly of a covalent organic–inorganic polyoxometalate (POM)-based hybrid. In this system, we take advantage of the presence of charged subunits (POM, metal linker, and counterions) within the metallomacrocycles, which drive their aggregation through intermolecular electrostatic interactions. We show that the solvent composition and the charge of the metal linker are key parameters that steer the supramolecular organization. Different types of hierarchical self-assemblies, zero-dimensional (0D) dense nanoparticles, and 1D worm-like nanoobjects, can be selectively formed owing to different aggregation modes of the metallomacrocycles. Finally, we report that the worm-like structures drastically enhance the solubility in water of a pyrene derivative and can act as molecular carriers.
    Mots-clés : E-POM, hierarchical self-assembly, molecular carrier, organic–inorganic hybrids, polyoxometalates, SAXS.
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  • Y. Ren, K. Cheaib, J. Jacquet, H. Vezin, L. Fensterbank, M. Orio, S. Blanchard, et M. Desage‐El Murr, « Copper-Catalyzed Aziridination with Redox-Active Ligands: Molecular Spin Catalysis », Chemistry – A European Journal, vol. 24, nᵒ 20, p. 5086-5090, avr. 2018.
    Résumé : Small-molecule catalysts as mimics of biological systems illustrate the chemists’ attempts at emulating the tantalizing abilities displayed by nature's metalloenzymes. Among these innate behaviors, spin multistate reactivity is used by biological systems as it offers thermodynamic leverage towards challenging chemical reactivity but this concept is difficult to translate into the realm of synthetic organometallic catalysis. Here, we report a rare example of molecular spin catalysis involving multistate reactivity in a small-molecule biomimetic copper catalyst applied to aziridination. This behavior is supported by spin state flexibility enabled by the redox-active ligand.
    Mots-clés : aziridination, copper catalysis, E-POM, MACO, multistate reactivity, POLE 1, POLE 2, redox-active ligands, spin catalysis.
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  • T. Zhang, L. Mazaud, L. - M. Chamoreau, C. Paris, A. Proust, et G. Guillemot, « Unveiling the Active Surface Sites in Heterogeneous Titanium-Based Silicalite Epoxidation Catalysts: Input of Silanol-Functionalized Polyoxotungstates as Soluble Analogues », ACS Catalysis, vol. 8, nᵒ 3, p. 2330-2342, mars 2018.
    Résumé : We report on a site-isolated model for Ti(IV) by reacting [Ti(iPrO)4] with the silanol-functionalized polyoxotungstates [XW9O34–x(tBuSiOH)3]3– (X = P, x = 0, 1; X = Sb, x = 1, 2) in tetrahydrofuran. The resulting titanium(IV) complexes [XW9O34–x(tBuSiO)3Ti(OiPr)]3– (X = P, 3; X = Sb, 4) were obtained in monomeric forms both in solution and in the solid state, as proved by diffusion NMR experiments and by X-ray crystallographic analysis. Anions 3 and 4 represent relevant soluble models for heterogeneous titanium silicalite epoxidation catalysts. The POM scaffolds feature slight conformational differences that influence the chemical behavior of 3 and 4 as demonstrated by their reaction with H2O. In the case of 3, the hydrolysis reaction of the isopropoxide ligand is only little shifted toward the formation of a monomeric [PW9O34(tBuSiO)3Ti(OH)]3– (5) species [log K = −1.96], whereas 4 reacted readily with H2O to form a μ-oxo bridged dimer {[SbW9O33(tBuSiO)3Ti]2O}6– (6). The more confined was the coordination site, the more hydrophobic was the metal complex. By studying the reaction of 3 and 4 with hydrogen peroxide using NMR and Raman spectroscopies, we concluded that the reaction leads to the formation of a titanium-hydroperoxide Ti-(η1-OOH) moiety, which is directly involved in the epoxidation of the allylic alcohol 3-methyl-2-buten-1-ol. The combined use of both spectroscopies also led to understanding that a shift of the acid–base equilibrium toward the formation of Ti(η2-O2) and H3O+ correlates with the partial hydrolysis of the phosphotungstate scaffold in 3. In that case, the release of protons also catalyzed the oxirane opening of the in situ formed epoxide, leading to an increased selectivity for 1,2,3-butane-triol. In the case of the more stable [SbW9O33(tBuSiO)3Ti(OiPr)]3– (4), the evolution to Ti(η2-O2) peroxide was not detected by Raman spectroscopy, and we performed reaction progress kinetic analysis by NMR monitoring the 3-methyl-2-buten-1-ol epoxidation to assess the efficiency and integrity of 4 as precatalyst.
    Mots-clés : E-POM, POLE 2.
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  • T. Zhang, A. Solé-Daura, S. Hostachy, S. Blanchard, C. Paris, Y. Li, J. J. Carbó, J. M. Poblet, A. Proust, et G. Guillemot, « Modeling the Oxygen Vacancy at a Molecular Vanadium(III) Silica-Supported Catalyst », Journal of the American Chemical Society, vol. 140, nᵒ 44, p. 14903-14914, nov. 2018.
    Résumé : Here we report on the use of a silanol-decorated polyoxotungstate, [SbW9O33(tBuSiOH)3]3– (1), as a molecular support to describe the coordination of a vanadium atom at a single-site on silica surfaces. By reacting [V(Mes)3·thf] (Mes = 2,4,6-trimethylphenyl) with 1 in tetrahydrofuran, the vanadium(III) derivative [SbW9O33(tBuSiO)3V(thf)]3– (2) was obtained. Compound 2 displays the paramagnetic behavior expected for a d2-VIII high spin complex (SQUID measurements) with a triplet electronic ground state (ca. 30 kcal·mol–1 more stable than the singlet, from DFT calculations). Compound 2 proves to be a reliable model for reduced isolated-vanadium atom dispersed on silica surfaces [(≡Si—O)3VIII(OH2)], an intermediate that is often proposed in a Mars–van Krevelen type mechanism for partial oxidation of light alcohols. Oxidation of 2 under air produced the oxo-derivative [SbW9O33(tBuSiO)3VO]3– (3). In compound 2, the d2-electrons are localized in degenerated d(V) orbitals, whereas in the electronically analogous bireduced-[SbW9O33(tBuSiO)3VO]5–, 3·(2e), one electron is localized on d(V) orbital and the second one is delocalized on the polyoxotungstic framework, leading to a unique case of a bireduced heteropolyanion derivative with completely decoupled d1-V(IV) and d1-W(V). Our body of experimental results (EPR, magnetic measurements, spectroelectrochemical studies, Raman spectroscopy) and theoretical studies highlights (i) the role of the apical ligand coordination, i.e., thf (σ-donor) vs oxo (π-donor), in destabilizing or stabilizing the d(V) orbitals relative to the d(W) orbitals, and (ii) a geometrical distortion of the O3VO entity that causes a splitting of the degenerated orbitals and the stabilization of one d(V) orbital in the bireduced compound 3·(2e).
    Mots-clés : E-POM, ERMMES, POLE 2.
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2017



  • Q. Arnoux, A. Boucly, V. Barth, R. Benbalagh, A. Cossaro, L. Floreano, M. Silly, F. Sirotti, E. Derat, S. Carniato, F. Bournel, J. - J. Gallet, D. Fichou, L. Tortech, et F. Rochet, « Energy-Level Alignment of a Hole-Transport Organic Layer and ITO: Toward Applications for Organic Electronic Devices », ACS Applied Materials & Interfaces, vol. 9, nᵒ 36, p. 30992-31004, sept. 2017.
    Résumé : 2,2′,6,6′-Tetraphenyl-4,4′-dipyranylidene (DIPO-Ph4) was grown by vacuum deposition on an indium tin oxide (ITO) substrate. The films were characterized by atomic force microscopy as well as synchrotron radiation UV and X-ray photoelectron spectroscopy to gain an insight into the material growth and to better understand the electronic properties of the ITO/DIPO-Ph4 interface. To interpret our spectroscopic data, we consider the formation of cationic DIPO-Ph4 at the ITO interface owing to a charge transfer from the organic layer to the substrate. Ionization energy DFT calculations of the neutral and cationic species substantiate this hypothesis. Finally, we present the energetic diagram of the ITO/DIPO-Ph4 system, and we discuss the application of this interface in various technologically relevant systems, as a hole-injector in OLEDs or as a hole-collector interfacial layer adjacent to the prototypical OPV layer P3HT:PCBM.
    Mots-clés : E-POM, POLE 1, POLE 2.
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