Dimerization of ion radicals in ionic liquids. An example of favourable "Coulombic" solvation.

International audienceThe irreversible dimerization of the acetophenone radical anion, chosen as an example of a carbon-carbon coupling reaction between two charged species, was investigated in a series of 1,3-dialkylimidazolium and 1,2,3-trialkylimidazolium ionic liquids. Indeed, such ion dimerizations which display slow kinetics despite small activation energies, are controlled by a subtle competition between bond formation, Coulombic repulsion and solvation. The effects of viscosity, "polarity" and ionic solvation on the reactivity of the radical anions were examined. The dimerization rate constants were demonstrated to be only weakly affected by the high viscosity of the medium or its apparent polarity. When the acetophenone radical anion is "solvated" in imidazolium-based ionic liquids, a strong interaction between the negatively-charged intermediates and the imidazolium cation occurs. The ensuing charge stabilization allows a fast dimerization step in all the ionic liquids used. The kinetic effect is even enhanced in the 1,3-dialkylimidazolium salts as compared to the 1,2,3-trialkylimidazolium ones because the interaction between the radical anions and the 1,3-dialkylimidazolium cations are stronger, probably due to the formation of H-bond. The reactivity of the ion radical is demonstrated not only to be mainly dominated by electrostatic interactions, but also that the nature of the ionic liquid cations with respect to that of the ion radical is a major factor that affects the reaction kinetics

Direct formation of fullerene monolayers using [4+2] Diels-Alder cycloaddition.

International audienceThe formation of covalent C(60) monolayers through [4+2] Diels-Alder cycloaddition between C(60) and anthracene monolayers grafted onto a silicon oxide surface was investigated by ellipsometry, fluorescence and by atomic force microscopy

Synthesis of Functionalized Few-Layer Graphene Through Fast Electrochemical Expansion of Graphite

International audienc

Optical electron transfer through 2,7-diethynylfluorene spacers in mixed-valent complexes containing electron-rich "(η2-dppe)(η5-C5Me5)Fe" endgroups.

International audienceWe report in this communication the study of the intramolecular electron transfer through a 2,7-diethynylfluorenyl spacer in the Fe(II)/Fe(III) mixed-valent (MV) complex [(η(2)-dppe)(η(5)-C(5)Me(5))FeC≡C(2,7-C(21)H(24))C≡CFe(η(5)-C(5)Me(5))(η(2)-dppe)][PF(6)] (1[PF(6)]). The complex is generated in situ by comproportionation from its homovalent dinuclear Fe(II) and Fe(III) parents (1 and 1[PF(6)](2)). It is shown that electronic delocalization is much more effective through a 2,7-fluorenyl than through a 4,4'-biphenyl bridging unit

Oxidation of Porphyrins in the Presence of Nucleophiles: From the Synthesis of Multisubstituted Porphyrins to the Electropolymerization of the Macrocycles

International audienc

Insights into water coordination associated with the Cu(II)/Cu(I) electron transfer at a biomimetic Cu centre.

International audienceThe coordination properties of the biomimetic complex [Cu(TMPA)(H2O)](CF3SO3)2 (TMPA = tris(2-pyridylmethyl)amine) have been investigated by electrochemistry combined with UV-Vis and EPR spectroscopy in different non-coordinating media including imidazolium-based room-temperature ionic liquids, for different water contents. The solid-state X-ray diffraction analysis of the complex shows that the cupric centre lies in a N4O coordination environment with a nearly perfect trigonal bipyramidal geometry (TBP), the water ligand being axially coordinated to Cu(II). In solution, the coordination geometry of the complex remains TBP in all media. Neither the triflate ion nor the anions of the ionic liquids were found to coordinate the copper centre. Cyclic voltammetry in all media shows that the decoordination of the water molecule occurs upon monoelectronic reduction of the Cu(II) complex. Back-coordination of the water ligand at the cuprous state can be detected by increasing the water content and/or decreasing the timescale of the experiment. Numerical simulations of the voltammograms allow the determination of kinetics and thermodynamics for the water association-dissociation mechanism. The resulting data suggest that (i) the binding/unbinding of water at the Cu(I) redox state is relatively slow and equilibrated in all media, and (ii) the binding of water at Cu(I) is somewhat faster in the ionic liquids than in the non-coordinating solvents, while the decoordination process is weakly sensitive to the nature of the solvents. These results suggest that ionic liquids favour water exchange without interfering with the coordination sphere of the metal centre. This makes them promising media for studying host-guest reactions with biomimetic complexes

Reversible Redox‐Driven Crystallization in a Paracyclophane Monolayer at a Solid–Liquid Interface

The development and integration of cyclophanes into future functional materials require a detailed understanding of the physicochemical principles that underlie their properties, phase behavior, and in particular the relationship between structure and function. Here, electrochemically switchable crystallization of a ferrocene‐bearing 3D Janus tecton (M‐Fc) at the interface between highly oriented pyrolytic graphite (HOPG) and an electrolyte solution is demonstrated. The M‐Fc adlayer is successfully visualized under both ambient and electrochemical conditions using scanning tunneling microscopy. Voltammetric measurements show a surface‐confined redox process for the M‐Fc modified surface that drives the phase transition between a visible 2D ordered linear phase (M‐Fc0, with ferrocene in the neutral state) and an invisible gas‐like adsorption layer with high mobility when ferrocene is oxidized, M‐Fc+, and a “square scheme” mechanism explains the data. Analogous experiments in a ferrocene‐free tecton adlayer show no phase transition and confirm that the dynamics in M‐Fc are redox‐driven. On‐surface 3D nanoarchitectures are also demonstrated by forming inclusion complexes between M‐Fc and β‐cyclodextrin and device behavior through electrochemical scanning tunneling spectroscopy (STS). These results showcase the functional potential of this class of cyclophanes, which can find use in actuators, optical crystals, and other smart materials

Catalyse homogene des reactions electrochimiques : couplage electronique entre diffusions, catalyse de la reduction de l'oxygene par le methylviologene

SIGLECNRS T 58501 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Application des ultramicroelectrodes a l'analyse cinetique de reactions rapides

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

La microscopie électrochimique à balayage : vers un véritable microscope chimique [Scanning electrochemical microscopy: towards a true chemical microscope]

National audienceElectrochem. methods based on the use of micro-sized electrode (UME) or smaller are a step forward in recent years. Scanning electrochem. microscopy (SECM) is used for probing the chem. properties of a surface. Its principle is based on the interaction of a chem. species generated in soln. at the UME with the surface to be probed. The principles of SECM, its advantages, possibilities and limitations will be developed and illustrated in this paper