Search

National audience; 1,4-Bis(carboxylatoethynyl)bicyclo[2.2.2]octane: un rotor ultra-rapide dans un sel dilué est freiné au sein d’un métal multifonctionnel1L’objectif de ce travail est la conception de systèmes dans lesquels les propriétés dynamiques d’une machine moléculaire seraient corrélées aux propriétés électroniques que l’on rencontre habituellement dans les matériaux conçus au laboratoire par la technique d’électrocristallisation. Pour cela un sel dilué de formulation [nBu4N+]2[BABCO][BABCO–]2 a été préparé à partir du 1,4-di(ethynyl)bicyclo[2.2.2]octane synthétisé en neuf étapes2. Des expériences de temps de relaxation spin-réseau du 1H sur cristal statique montrent que deux environnements différents des rotors sont associés à des énergies d’activation et des fréquences de rotation différentes.Ce sel a été engagé dans un processus d’électrocristallisation avec le donneur d’électrons de type π EDT-TTF-CONH2 pour donner un nouveau métal organique cristallin : (EDT-TTF-CONH2)2[BABCO–], pour la première fois avec une fonctionnalité dynamique. Une seule position d’équilibre est observée pour le rotor dont on observe que l’énergie d’activation est grandement augmentée: ceci pourrait être attribué à des contraintes à la rotation accrues, expression d’un réseau dense d’interactions non covalentes (liaisons hydrogènes et interactions dihydrogène attractives3).Ce matériau organique métallique ouvre la voie à d’autres systèmes multifonctionnels amphidynamiques.1C. Lemouchi, C. Mézière, L. Zorina, E. Canadell, P. Wzietek, P. Auban-Senzier, C. Pasquier, P. Batail, soumis2C. Lemouchi, C. Vogelsberg, S. Simonov, L. Zorina, P. Batail, S. Brown, M. A. Garcia-Garibay, J. Am. Chem. Soc., 133, 6371-6379 (2011).3J. Echeverrıa, G. Aullon, D. Danovich, S. Shaik, S. Alvarez, Nature Chem., 2011, DOI: 10.1038/nchem.1004

International audience; Strong I***O halogen bonds are identified in a series of cation radical salts of the donor molecule 3,4-diiodo-3′,4′-ethylenedithiotetrathiafulvalene (EDT-TTFI2, 1) with ClO4- and various organic sulfonates, such as racemic camphor sulfonate, 1,5- and 2,6-naphtalene bis(sulfonate), and 2,6-anthracene bis(sulfonate). In all compounds, oxygen atoms of sulfonate moieties appear thus as powerful halogen bonding acceptors with I***O distance much shorter than the van der Waals contacts (down to 77%). A full charge transfer (ρ = 1) is found in (1)ClO4 and (1)2[2,6-Napth(SO3)2], with a dimerization of the stacks of 1*+ cation radicals and a diamagnetic behavior. The mixed-valence (ρ = 1/2) salts (1)2[(rac)-camph(SO3)]*Solv, (1)5[2,6-Anthr(SO3)2], and (1)4[1,5-Napht(SO3)2] form conducting stacks with semiconducting behavior. Band structure calculations and magnetic measurements performed on (1)4[1,5-Napht(SO3)2] show a strongly one-dimensional electronic structure, at the origin of the semiconducting behavior.

International audience; An investigation of the P-T phase diagram of the quarter-filled organic conductors, [EDT-TTF-CONMe2]2X is reported on the basis of transport and NMR studies of two members, X=AsF6 and Br of the family. The strongly insulating character of these materials in the low-pressure regime has been attributed to a remarkably stable charge-ordered state confirmed by 13C NMR and the only existence of 1/4 Umklapp e-e scattering favoring a charge ordering instead of the 1D Mott localization seen in (TMTTF)2X and (TMTSF)2X which are 1/4-filled compounds with dimerization. A nonmagnetic insulating phase instead of the spin density wave state is stabilized in the deconfined regime of the phase diagram. This sequence of phases observed under pressure may be considered as a generic behavior for 1/4-filled conductors with correlations.

Champ "Titre" tronqué, voir ci-dessous pour le titre complet:Modulating the Framework Negative Charge Density in the System [BDT−TTP•+]/[Re6S5Cl91-]/[Re6(S/Se)6Cl82-]/[Re6S7Cl73-]: Templating by Isosteric Cluster Anions of Identical Symmetry and Shape, Variations of Incommensurate Band Filling, and Electronic Structure in 2D Metals; International audience; A series of 2D metals, β-(BDT-TTP)6[Re6Se6Cl8]·(CHCl2−CHCl2)2, 2; β-(ST-TTP)6[Re6S6Cl8]·(CH2Cl−CHCl2)2, 3; β-(BDT-TTP)7[Re6S6Cl8]0.5[Re6S7Cl7]0.5·(CH2Cl2), 4; β-(BDT-TTP)7[Re6Se6Cl8]0.5[Re6S7Cl7]0.5·(CH2Cl2), 5; β-(BDT-TTP)8[Re6S7Cl7]·(CH2Cl2)4, 6 (BDT-TTP and ST-TTP are 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene and 2-(1,3-diselenol-2-ylidene)-5(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene, respectively) is reported to have one single β-slab layered topology despite successive increases of the cluster anion negative charge. The charge density within the templating composite inorganic−neutral molecule slab is shown to remain above a threshold of ca. one negative charge per square nanometer, that is, for cluster anions with two negative charges and higher. Conversely, discrete stacks are shown to be stabilized instead in the semiconducting salts (BDT-TTP)2[Re6S5Cl9], 1 where the cluster anion bears one negative charge only. The electronic structure of salts 2−6 is shown to be very stable and kept almost intact across the series. The templating strategy is shown to fulfill its anticipated potential for deliberate installment of incommensurate band fillings in molecular metals. The deliberate admixture of the 6:1 and 8:1 structures yields novel phases with a 7:1 stoichiometry with the anticipated crystal and electronic structures. The action at the organic−inorganic interface triggered by changing the anion charge yet keeping its shape and volume identical, which ultimately governs the shape of the unit cell, is of paramount importance in defining the Fermi surface of these metallic salts. The present BDT-TTP salts thus provide a series of materials with strongly related but subtly different Fermi surfaces worthy of many physical studies. Shubnikov−de Haas measurements are expected to be particularly interesting since they are especially sensitive to the details of the Fermi surface.

The phase diagram of the organic superconductor (TMTSF)_2PF_6 has been revisited using transport measurements with an improved control of the applied pressure. We have found a 0.8 kbar wide pressure domain below the critical point (9.43 kbar, 1.2 K) for the stabilisation of the superconducting ground state featuring a coexistence regime between spin density wave (SDW) and superconductivity (SC). The inhomogeneous character of the said pressure domain is supported by the analysis of the resistivity between T_{SDW} and T_{SC} and the superconducting critical current. The onset temperature T_{SC} is practically constant, 1.20 +/- 0.01 K, in this region where only the SC/SDW domain proportion below T_{SC} is increasing under pressure. An homogeneous superconducting state is recovered above the critical pressure with T_{SC} falling at increasing pressure. We propose a model comparing the free energy of a phase exhibiting a segregation between SDW and SC domains and the free energy of homogeneous phases which explains fairly well our experimental findings.

We report a detailed characterization of quantum Hall effect (QHE) influence on the linear and non-linear resistivity tensor in FISDW phases of the organic conductor (TMTSF)_2PF_6. We show that the behavior at low electric fields, observed for nominally pure single-crystals with different values of the resistivity ratio, is fully consistent with a theoretical model, which takes QHE nature of FISDW and residual quasi-particle density associated with different crystal imperfection levels into account. The non-linearity in longitudinal and diagonal resistivity tensor components observed at large electric fields reconciles preceding contradictory results. Our theoretical model offers a qualitatively good explanation of the observed features if a sliding of the density wave with the concomitant destruction of QHE, switched on above a finite electric field, is taken into account.

Izvješćujemo o detaljnoj raščlambi utjecaja kvantnog Hall efekta (QHE) na tenzor vodljivosti organskog supravodiča (TMTSF)2PF6 u stanju vala gustoće spina induciranog magnetskim poljem (FISDW). Proučavani su monokristalni, nominalno čisti uzorci, različitih omjera otpornosti (omjer otpora na 300K i na 15K). Te omjere povezujemo sa različitim koncentracijama kristalnih defekata. Pokazali smo da je ponašanje u linearnom režimu električnog transporta i BEZ VEZNIKA I kvantitativno u POTPUNOM SKLADU potpunosti u skladu s vrlo jednostavnim teorijskim modelom NEPOTREBNO OVO IZA koji smo postavili. U OSNOVI MODELA SMO UVAZILI TENZORSKU PRIRODU ITD Za postavljanje modela je bilo dovoljno uzeti (tenzorsku) QHE prirodu vodljivosti FISDW stanja i kao dodatni parametar rezidualnu gustoću kvazi-čestica određenu iz omjera otpornosti. Nadalje, u sklopu modela smo uspjeli kvalitativno objasniti uočeno nelinearno ponašanje longitudinalnih i dijagonalnih komponenata tenzora vodljivosti pri velikim električnim poljima. Time smo dotadašnje kontradiktorne eksperimentalne rezultate pomirili i eksperimentalno i teorijski. U osnovi našeg shvaćanja nelinearnog režima jest da uz proklizavanje vala gustoće iznad nekog elektičnog polja u obzir treba uzeti i istovremeni nestanak kvantnog Hall efekta

An investigation of the different contributions leading to charge localization in a 1/2 or 1/4 filled band 1D conductor has been conducted through a study of transport properties in the solid solution [(TMTSF)_(1-x)(TMTTF)_x]_2ReO_4. The existence of an ordering transition of the anions allows to identify two contributions to the electronic potential with wave vector 4k_F. A dominant on-site 4k_F potential besides the bond contribution is revealed when Umklapp scattering is pertinent via the weakening of the localization arising at the (0, 1/2, 1/2) anion ordering which is stabilized under pressure in the compound [(TMTSF)_0.5(TMTTF)_0.5]_2ReO_4 at variance with the enhancement of localization observed in the homomolecular (TMTTF)_2ReO_4 material.