Mott transition, antiferromagnetism, and unconventional superconductivity in layered organic superconductors

The phase diagram of the layered organic superconductor $\kappa$-(ET)$_{2}$Cu[N(CN)$_{2}$]Cl has been accurately measured from a combination of $^{1}$H NMR and AC susceptibility techniques under helium gas pressure. The domains of stability of antiferromagnetic and superconducting long-range orders in the pressure {\it vs} temperature plane have been determined. Both phases overlap through a first-order boundary that separates two regions of inhomogeneous phase coexistence. The boundary curve is found to merge with another first order line related to the metal-insulator transition in the paramagnetic region. This transition is found to evolve into a crossover regime above a critical point at higher temperature. The whole phase diagram features a point-like region where metallic, insulating, antiferromagnetic and non s-wave superconducting phases all meet.Comment: 4 pages, 6 figures, Revte

A sulfur-rich pi-electron acceptor derived from 5,5 '-bithiazolidinylidene: charge-transfer complex vs. charge-transfer salt

International audienceNovel pi-electron acceptors are still highly desirable for the formation of conducting salts or as n-dopable semiconductors. We describe here two synthetic approaches to substitute a dicyanovinylidene group, C=C(CN)(2) to a thioketone (C=S) in the recently described DEBTTT acceptor where DEBTTT stands for (E)-3,3'-diethyl-5,5'-bithiazolidinylidene-2,4,2',4'-tetrathione. These electron withdrawing groups enhance the electron accepting ability as demonstrated through electrochemical investigations, without hindering the formation of short intra-and intermolecular S center dot center dot center dot S contacts in the solid state. Association of this acceptor 1 with tetramethyltetrathiafulvalene (TMTTF) and decamethylferrocene (Fe(Cp*)(2)) afforded 1 : 1 adducts which were analyzed by single crystal X-ray diffraction. Combined with vibrational and magnetic properties, it appears that [TMTTF][1] behaves as a neutral charge-transfer complex while [Fe(Cp*)(2)][1] is an ionic salt. The concentration of the spin density on the exocyclic sulfur atoms in 1(-center dot) favors the setting of direct anti-ferromagnetic interactions in [Fe(Cp*)(2)][1

Anisotropic Charge Distribution and Anisotropic van der Waals Radius Leading to Intriguing Anisotropic Noncovalent Interactions

Although group (IV-VII) nonmetallic elements do not favor interacting with anionic species, there are counterexamples including the halogen bond. Such binding is known to be related to the charge deficiency because of the adjacent atom's electron withdrawing effect, which creates s/p-holes at the bond-ends. However, a completely opposite behavior is exhibited by N-2 and O-2, which have electrostatically positive/negative character around cylindrical-bond-surface/bond-ends. Inspired by this, here we elucidate the unusual features and origin of the anisotropic noncovalent interactions in the ground and excited states of the 2nd and 3rd row elements belonging to groups IV-VII. The anisotropy in charge distributions and van der Waals radii of atoms in such molecular systems are scrutinized. This provides an understanding of their unusual molecular configuration, binding and recognition modes involved in new types of molecular assembling and engineering. This work would lead to the design of intriguing molecular systems exploiting anisotropic noncovalent interactions.open

Metal Hydrides Form Halogen Bonds: Measurement of Energetics of Binding

The formation of halogen bonds from iodopentafluorobenzene and 1-iodoperfluorohexane to a series of bis(η5-cyclopentadienyl)metal hydrides (Cp2TaH3, 1; Cp2MH2, M = Mo, 2, M = W, 3; Cp2ReH, 4; Cp2Ta(H)CO, 5; Cp = η5-cyclopentadienyl) is demonstrated by 1H NMR spectroscopy. Interaction enthalpies and entropies for complex 1 with C6F5I and C6F13I are reported (ΔH° = −10.9 ± 0.4 and −11.8 ± 0.3 kJ/mol; ΔS° = −38 ± 2 and −34 ± 2 J/(mol·K), respectively) and found to be stronger than those for 1 with the hydrogen-bond donor indole (ΔH° = −7.3 ± 0.1 kJ/mol, ΔS° = −24 ± 1 J/(mol·K)). For the more reactive complexes 2–5, measurements are limited to determination of their low-temperature (212 K) association constants with C6F5I as 2.9 ± 0.2, 2.5 ± 0.1, <1.5, and 12.5 ± 0.3 M–1, respectively

2'-(1,3-Dithiolan-2-ylidene)-4'-(1,3-dithiol-2-ylidene)spiro[1,3-dithiole-2,5'-(4' H -5',6'-dihydro-1',3'-dithiapentalene)], the Self-Condensation Product of an Extended Tetrathiafulvalene Derivative

International audienceSiO2-​gel treatment of the extended tetrathiafulvalene derivative 2,​3-​bis(1,​4-​dithiafulven-​6-​yl)​-​6,​7-​dihydrotetrathiafulvalene, bearing two 1,​4-​dithiafulven-​6-​yl groups in vicinal positions, afforded the title compound, C14H10S8, as a cyclization product. While one dithiafulvenyl group is still conjugated with the tetrathiafulvalene moiety, the other one gives rise to a strongly folded 1,​3-​dithiole group linked to the molecule through a spiro-​C atom. Two short nonbonding intramolecular 1,​5-​S···S contacts are also identified in the title compound

Turbulence et diffusion d'un gaz lourd dans l'atmosphère

L'émission dans l'atmosphère d'un gaz polluant ou inflammable est un des risques potentiels de l'industrie chimique. L'étude décrite a été entreprise en vue de prédire l'évolution d'un gaz lourd près de son point d'émission. Elle a été réalisée à l'aide du système TRIO de logiciels de calcul d'écoulements turbulents tridimensionnels, destiné, à l'origine, au calcul des phénomènes thermohydrauliques mis en jeu dans les installations nucléaires. La variété des phénomènes présents dans ces installations a conduit à la réalisation de logiciels de résolution de problèmes thermohydrauliques généraux: un logiciel fondé sur la méthode des éléments finis (TRIO.EF), un logiciel fondé sur la méthode des volumes finis (TRIO.VF). Ils utilisent une modélisation de la turbulence du type (k, ε) avec prise en compte des effets de densité. Les prédictions du logiciel TRIO.VF sont comparées avec des essais de rejet d'un gaz lourd réalisés sur le site de Thorney Island dans le cadre d'un programme européen