136 research outputs found
Mixed-valence gold bis (diselenolene) complex turning metallic under pressure.
While oxidation of d8 anionic gold bis(dithiolene) complexes most often affords the corresponding neutral radical single-component conductor, an original gold bis(diselenolene) complex isolated as a Ph4P+ salt affords upon electrocrystallization a mixed-valence 1â:â2 salt, [Ph4P][Au(Me-thiazds)2]2 (Me-thiazds: 2-methyl-1,3-thiazoline-2-thione-4,5-diselenolate). This salt exhibits a rare charge alternation associated with the simultaneous presence of both cis and trans isomers of the gold complex in the conducting layers. The salt is semiconducting (ÏRT = 3 Ă 10â2 S cmâ1, Eact = 0.137 eV) but, in contrast with other 1â:â2 gold bis(dithiolene) salts, turns metallic under pressure (>10 GPa). [Ph4P][Au(Me-thiazds)2]2 is thus the first metallic, fully characterized, 1â:â2 mixed-valence gold complex, opening the door for the preparation of highly conducting solids of this type
Finite-Temperature Properties across the Charge Ordering Transition -- Combined Bosonization, Renormalization Group, and Numerical Methods
We theoretically describe the charge ordering (CO) metal-insulator transition
based on a quasi-one-dimensional extended Hubbard model, and investigate the
finite temperature () properties across the transition temperature, . In order to calculate dependence of physical quantities such as the
spin susceptibility and the electrical resistivity, both above and below
, a theoretical scheme is developed which combines analytical
methods with numerical calculations. We take advantage of the renormalization
group equations derived from the effective bosonized Hamiltonian, where Lanczos
exact diagonalization data are chosen as initial parameters, while the CO order
parameter at finite- is determined by quantum Monte Carlo simulations. The
results show that the spin susceptibility does not show a steep singularity at
, and it slightly increases compared to the case without CO because
of the suppression of the spin velocity. In contrast, the resistivity exhibits
a sudden increase at , below which a characteristic dependence
is observed. We also compare our results with experiments on molecular
conductors as well as transition metal oxides showing CO.Comment: 9 pages, 8 figure
Molecular and thin film properties of cobalt half-sandwich compounds for optoelectronic application
The structure and electronic properties of a novel cobalt half sandwich
complex of cyclopentadiene (Cp) and diaminonaphthalene (DAnap) [CpCo(DAnap)]
are described and compared to the previously reported diaminobenzene
derivative [CpCo(DAbnz)] in view of their potential for (opto)electronic
device application. Both complexes show stable redox processes, tunable
through the diaminoacene ligand, and show strong absorption in the visible
region, with additional transitions stretching into the near infrared (NIR).
CpCo(DAnap) crystallises with a particularly large unit cell (9301 Ă
3),
comprising 32 molecules, with a gradual rotation over 8 molecules along the
long c-axis. In the solid state the balance of the optical transitions in both
complexes is reversed, with a suppression of the visible band and an
enhancement of the NIR band, attributed to extensive intermolecular electronic
interaction. In the case of CpCo(DAnap), highly crystalline thin films could
be formed under physical vapor deposition, which show a photocurrent response
stretching into the NIR, and p-type semiconductor behavior in field effect
transistors with mobility values of the order 1 Ă 10â4 cm2 Vâ1 sâ1. The device
performance is understood through investigation of the morphology of the grown
films
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
New Trends in Beverage Packaging Systems: A Review
New trends in beverage packaging are focusing on the structure modification of packaging materials and the development of new active and/or intelligent systems, which can interact with the product or its environment, improving the conservation of beverages, such as wine, juice or beer, customer acceptability, and food security. In this paper, the main nutritional and organoleptic degradation processes of beverages, such as oxidative degradation or changes in the aromatic profiles, which influence their color and volatile composition are summarized. Finally, the description of the current situation of beverage packaging materials and new possible, emerging strategies to overcome some of the pending issues are discussed
Open Bis(triazolium) Structural Motifs as a Benchmark To Study Combined Hydrogen- and Halogen-Bonding Interactions in Oxoanion Recognition Processes
La liaison halogĂšne [Halogen bonding]
National audienceHalogen bonding, by analogy with hydrogen bonding, describes an intermolecular interaction where an activated halogen atom acts as electrophile through its s-hole area toward a Lewis base. This paper describes its main characteristics and its involvement in many domains, such as crystal engineering, polymers and gels, biomolecular systems or organocatalysis. © 2018 Societe Francaise de Chimie. All rights reserved
The salt-co-crystal continuum in halogen-bonded systems
International audience[No abstract available
Unsymmetrically-Substituted Tetrathiafulvalenes (TTF) as Key Intermediates in the Preparation of Functionalized TTF Derivatives
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