Magnetoelastic effects in Jahn-Teller distorted CrF2_2 and CuF2_2 studied by neutron powder diffraction

We have studied the temperature dependence of crystal and magnetic structures of the Jahn-Teller distorted transition metal difluorides CrF$_2$ and CuF$_2$ by neutron powder diffraction in the temperature range 2-280 K. The lattice parameters and the unit cell volume show magnetoelastic effects below the N\'eel temperature. The lattice strain due to the magnetostriction effect couples with the square of the order parameter of the antiferromagnetic phase transition. We also investigated the temperature dependence of the Jahn-Teller distortion which does not show any significant effect at the antiferromagnetic phase transition but increases linearly with increasing temperature for CrF$_2$ and remains almost independent of temperature in CuF$_2$. The magnitude of magnetovolume effect seems to increase with the low temperature saturated magnetic moment of the transition metal ions but the correlation is not at all perfect

Influence of the electrografting method on the performances of a flow electrochemical sensor using modified electrodes for trace analysis of copper (II).

International audienceThe performances of carboxylate- and cyclam-modified graphite felt electrodes prepd. by different electrografting methods for trace anal. of copper (II) were compared to det. the influence of the immobilization process of the linkers on the sensor properties. The derivatization performed by cathodic redn. of diazonium salts and by anodic oxidn. of amines in org. and aq. media was first evaluated by cyclic voltammetry and XPS analyses, showing a higher surface coverage for the redn. process. Cyclam was subsequently attached on the COOH-modified graphite felts by a coupling reaction. The modified electrodes were then employed in a flow anal. system for trace anal. of copper (II) ions. The influence of the surface coverage and the nature of the linker on the electrochem. signal obtained by linear sweep stripping voltammetry anal. after a preconcn. step performed at open circuit was highlighted. The selectivity estd. in the presence of lead used as a common ion interferent was higher when a selective receptor was used and depends on the nature of the linker. [on SciFinder(R)

Palladium nanoparticles supported on fluorine-doped tin oxide as an efficient heterogeneous catalyst for Suzuki coupling and 4-nitrophenol reduction

Immobilization of palladium nanoparticles onto the fluorine-doped tin oxide (FTO) as support Pd/FTO, resulted in a highly active heterogeneous catalyst for Suzuki-Miyaura cross-coupling reactions and 4-nitrophenol reduction. The Pd/FTO catalyst has been synthesized by immobilization of palladium nanoparticles onto FTO via a simple impregnation method. ICP-MS analysis confirmed that there is 0.11 mmol/g of palladium was loaded successfully on FTO support. The crystallinity, morphologies, compositions and surface properties of Pd/FTO were fully characterized by various techniques. It was further examined for its catalytic activity and robustness in Suzuki coupling reaction with different aryl halides and solvents. The yields obtained from Suzuki coupling reactions were basically over 80%. The prepared catalyst was also tested on mild reaction such as reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). Pd/FTO catalyst exhibited high catalytic activity towards 4-NP reduction with a rate constant of 1.776 min(-1) and turnover frequency (TOF) value of 29.1 hr(-1). The findings revealed that Pd/FTO also maintained its high stability for five consecutive runs in Suzuki reactions and 4-NP reductions. The catalyst showed excellent catalytic activities by using a small amount of Pd/FTO for the Suzuki coupling reaction and 4-NP reduction

histoire, applications et paradoxes

Paris, 28 juin 1886. Henri Moissan réussit à isoler le fluor (F2). Cette expérience fondamentale, qui vaudra à la France son premier prix Nobel de Chimie (1906), ouvre une ère nouvelle. Ce gaz jaune, d’odeur irritante, réagit avec quasiment toutes les substances et leur confère des propriétés exceptionnelles de plasticité et d’inertie chimique. Ses applications sont innombrables et, en quelques années, le fluor devient un élément incontournable de l’industrie. Il joue aujourd’hui un rôle déterminant dans les procédés de production de l’aluminium, de l’énergie nucléaire et du silicium nécessaire aux nouvelles technologies.Dans tous les domaines industriels, de la médecine à l’agrochimie, ce sont plus de 600 000 composés qui utilisent ses qualités. Teflon®, Gore-Tex®, anti-graffiti, anti-feu, médicaments anticancéreux, antibiotiques, neuroleptiques, biomatériaux, pesticides, batteries à lithium-ion et piles à combustible (à membranes polymères) n’existeraient pas sans lui.Mais cet élément quasi magique a ses paradoxes : la production d’aluminium dégage des perfluorocarbones (PFC), difficilement éliminables. Les CFC, utilisés pour la réfrigération, rognent la couche d’ozone. À des doses raisonnables, la présence du fluor dans l’eau renforce l’émail des dents, mais, en excès, provoque de terribles maladies.Un livre magistral qui conte l’histoire passionnante du fluor en retraçant sa découverte et en décryptant ses applications scientifiques et ses implications sur l’homme et son environnement

Progress in Science, Progress in Society

This book addresses current societal debates around the globe. Written by respected researchers from France, Germany, Belgium, Denmark, Spain, Portugal and Italy, the chapters are based on presentations given at a conference organized by the European Academy of Sciences, in partnership with the Royal Academy of Belgium and French Academy of Sciences, in Brussels (Belgium) in November 2016

Sur quelques nouveaux composés fluorés du fer

Thèse de 3ème cycle soutenue à la Faculté des Sciences de l'Université de BordeauxJusqu'à ces dernières années, la chimie des composés fluorés des éléments de transition n'avait pas connu un grand développement. Les rares travaux effectués avaient été entrepis par voie aqueuse. Les études en phase solide étaient pratiquement inexistantes en raison sans doute des difficultés techniques auxquelles se heurtaient les expérimentateurs.Depuis 1958, les composés fluorés ou oxyfluorés ont connu un regain d'intérêt. La substitution partielle ou totale de l'oxygène par le fluor, en raison de la proximité de leurs rayons ioniques, permettait d'obtenir de nouvelles séries isomorphes des oxydes...non disponibl

Analyse physico-chimique des tissus calcifiés osseux et dentaires

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