Magnetocaloric effect in hexacyanochromate Prussian blue analogs

We report on the magnetocaloric properties of two molecule-based hexacyanochromate Prussian blue analogs, nominally CsNi[Cr(CN)_6](H_2O) and Cr_3[Cr(CN)_6]_2x12(H_2O). The former orders ferromagnetically below Tc=90 K, whereas the latter is a ferrimagnet below Tc=230 K. For both, we find significantly large magnetic entropy changes DSm associated to the magnetic phase transitions. Notably, our studies represent the first attempt to look at molecule-based materials in terms of the magnetocaloric effect for temperatures well above the liquid helium range.Comment: 4 pages, 6 figure

Seuils d'absorption des rayons X : un outil de caractérisation indispensable en chimie de coordination.

National audienceSynchrotron radiation allows to perform spectroscopic experiments in an energy range from infra-red to hard X-rays. The paper shows, through particular examples (role of the geometry, of the oxidation and spin state of the absorber ...) how it is possible to extract unique informations from X-ray absorption edges to characterize the electronic structure of the absorbing elements whatever the state of the sample (crystalline, amorphous, liquid, solution, gaseous). The interpretation of the data is proposed at a double level : qualitative, thanks to symmetry theory and more quantitative, thanks to quantum calculations

Antiferromagnetic interactions in copper(II) mu-Oxalato dinuclear complexes: The role of the counterion

We report the preparation, crystal structure determination, magnetic properties and DFT calculations of five oxalato-bridged dicopper(II) complexes of formula [Cu-2(bpy)(2-)(H2O)(2)(C2O4)](CF3SO3)(2) (1), [Cu-2(bpy)(2)(C2O4)](PF6)(2) (2), [Cu-2(bpy)(2)(C2O4)](ClO4)(2) (3), [Cu-2(bpy)(2)Cl-2(C2O4)]center dot H2O (4) and [Cu-2(bpy)(2)(NO2)(2)(C2O4)] (5) (bpy = 2,2'-bipyridine and C2O42-= oxalate). Compounds 1, 2, 4 and 5 crystallize in the monoclinic system and 3 crystallizes in the triclinic system. The oxalate ligands in 1-5 adopt the bis-bidentate coordination mode and the two bpy molecules act as terminal ligands. The coordination of the counterions and the surroundings of the copper(II) ions differentiate the five compounds. The four nearest neighbours of copper(II) in 1-4 are roughly in the plane of the CuC2O4Cu framework, whereas they are in an almost perpendicular plane in 5. Using the isotropic Hamiltonian H = -JS(1)center dot S-2, where S-1 and S-2 are the spin quantum operators for Cu-1 and Cu-2; J is -384 cm(-1) for 1, -392 cm(-1) for 2 and -387 cm(-1) for 3, slightly decreasing to -328 cm(-1) for 4 and falling to -14 cm(-1) for 5. The influence of the anions on the magnetic properties of this family of compounds is explained by the changes in the overlap of the magnetic orbitals through the oxalate bridge. DFT calculations reproduce well the experimental values of J and provide an illustration of the magnetic orbitals

Cyanide-bridged Fe(III)–Co(II) bis double zigzag chains with a slow relaxation of the magnetisation

Reaction of [FeIII(bipy)(CN)4]¯ with fully solvated MII cations [M = Co (1) and Mn (2)] produces the isostructural bis double zigzag chains [[FeIII(bipy)(CN)4]2MII(H2O)]·MeCN·1/2H2O; 1 exhibits intrachain ferromagnetic and interchain antiferromagnetic couplings, slow magnetic relaxation and hysteresis effects.Luminita Marilena, Toma, [email protected] ; Lescouezec, Alain Francois Rodri, [email protected] ; Lloret Pastor, Francisco, [email protected] ; Julve Olcina, Miguel, [email protected]

Magnétisme et chiralité (des réseaux tridimensionnels à pont oxalate aux chaînes à pont verdazyl)

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

The fruitful introduction of chirality and control of absolute configurations in molecular magnets

International audienc

SYSTEMES A PRECURSEURS CYANOMETALLATES (COUCHES MINCES A HAUTES TEMPERATURES DE CURIE ET DERIVES D'OCTACYANOMETALLATES)

LA PREMIERE PARTIE DU TRAVAIL DE THESE A CONSISTE A METTRE SOUS FORME DE COUCHES MINCES MICRONIQUES UN ANALOGUE DU BLEU DE PRUSSE, CHROMICYANURE DE VANADIUM DONT LA TEMPERATURE DE CURIE PEUT ATTEINDRE 376 K. CETTE MISE EN FORME S'EST EFFECTUEE PAR ELECTROCHIMIE. LES COUCHES MINCES OBTENUES PRESENTENT DES TEMPERATURES DE CURIE T C QUI ATTEIGNENT 330 K. DES MESURES DE MAGNETO-OPTIQUE REALISEES DE 2 K A 373 K METTENT EN EVIDENCE LE CARACTERE POLYPHASE DU COMPOSE ET LA PRESENCE D'UNE HYSTERESIS MAGNETO-OPTIQUE A 373 K (0\C). NOUS MONTRONS L'INTERET ET LES LIMITES DE L'UTILISATION DES IONS DES DEUXIEME ET TROISIEME SERIES DES METAUX DE TRANSITION (CARACTERE DIFFUS DES ORBITALES D, EFFETS RELATIVISTES) POUR OBTENIR DES INTERACTIONS D'ECHANGE MAGNETIQUE OU DES ANISOTROPIES PLUS ELEVEES QUE POUR LES IONS DES METAUX DE LA PREMIERE SERIE DE TRANSITION. DANS LA SECONDE PARTIE DU MANUSCRIT, NOUS DECRIVONS LES STRUCTURES ET LES PROPRIETES DE COMPLEXES SYNTHETISES A PARTIR DE PRECURSEURS OCTACYANOMETALLATE M(CN) 8 Q , M = NB I V, MO I V, W I V, W V. NOUS DECRIVONS UNE STRUCTURE TRIDIMENSIONNELLE PRESENTANT UNE TEMPERATURE DE CURIE DE 50 K ENVIRON, UNE CHAINE DE TOPOLOGIE ORIGINALE PRESENTANT UNE ALTERNANCE D'INTERACTIONS FERRO- ET ANTIFERROMAGNETIQUES ET UNE MOLECULE A HAUT SPIN (S = 13/2). DES SYNTHESES DE MOLECULES A PARTIR DE PRECURSEURS OCTACYANOMETALLATE ET DE CATIONS PERIPHERIQUES M I IL 5(H 2O) 2 + (M = CO, NI ; L 5 LIGAND PENTADENTE) SONT DECRITES.PARIS-BIUSJ-Thèses (751052125) / SudocCentre Technique Livre Ens. Sup. (774682301) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Electrons in molecules: from basic principles to molecular electronics

This book provides the reader with a unified understanding of the rapidly expanding field of molecular materials and devices: electronic structures and bonding, magnetic, electrical and photo-physical properties, and the mastering of electrons in molecular electronics. This revised edition includes updates and additions on hot topics such as molecular spintronics (the role of spin in electron transport) and molecular machines (how electrons can generate molecular motions). Chemists will discover how to understand the relations between electronic structures and properties of molecular entities and assemblies, and to design new molecules and materials. Physicists and engineers will realize how the molecular world fits in with their need for systems flexible enough to check theories or provide original solutions to exciting new scientific and technological challenges. The non-specialist will find out how molecules behave in electronics at the most minute, sub-nanosize level