44 research outputs found
Mott transition, antiferromagnetism, and unconventional superconductivity in layered organic superconductors
The phase diagram of the layered organic superconductor
-(ET)Cu[N(CN)]Cl has been accurately measured from a
combination of 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
Crystalline Bi4Ge3O12 fibers fabricated by micro-pulling down technique for optical high voltage sensing
AbstractCommonly optical high voltage sensors employ the Pockels effect in a bulk electro-optic crystal such as Bi4Ge3O12 (BGO). Typically, the maximum crystal length is 100-200mm and determined by the limits of the conventional growth technique (Czochralski). In this paper we report on the growth by a micro-pulling down technique of long single crystalline BGO fibers as an alternative to bulk crystals and their characterization for voltage sensing. The fiber thickness may range from a few 100ÎŒm to a few mm. The parameters needed for stable growth over the entire length of the crystal were analyzed and optimized. Thin rods with a length of up to 850mm were grown. Samples were characterized with respect to homogeneity of growth, residual birefringence (BGO is free of natural birefringence), crystal orientation, and performance under voltage
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 (ÎH° = â10.9 ± 0.4 and â11.8 ± 0.3 kJ/mol; ÎS° = â38 ± 2 and â34 ± 2 J/(mol·K), respectively) and found to be stronger than those for 1 with the hydrogen-bond donor indole (ÎH° = â7.3 ± 0.1 kJ/mol, ÎS° = â24 ± 1 J/(mol·K)). For the more reactive complexes 2â5, 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 Mâ1, respectively
On the Reliability of Pure and Hybrid DFT Methods for the Evaluation of Halogen, Chalcogen, and Pnicogen Bonds Involving Anionic and Neutral Electron Donors
Excited States in Electron-Transfer Reaction Products: Ultrafast Relaxation Dynamics of an Isolated Acceptor Radical Anion
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-âgel treatment of the extended tetrathiafulvalene derivative 2,â3-âbis(1,â4-âdithiafulven-â6-âyl)â-â6,â7-âdihydrotetrathiafulvalene, bearing two 1,â4-âdithiafulven-â6-âyl 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,â3-âdithiole group linked to the molecule through a spiro-âC atom. Two short nonbonding intramolecular 1,â5-âS···S contacts are also identified in the title compound