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 1 : 2 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 (σRT = 3 × 10−2 S cm−1, Eact = 0.137 eV) but, in contrast with other 1 : 2 gold bis(dithiolene) salts, turns metallic under pressure (>10 GPa). [Ph4P][Au(Me-thiazds)2]2 is thus the first metallic, fully characterized, 1 : 2 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 ($T$) properties across the transition temperature, $T_{\rm CO}$. In order to calculate $T$ dependence of physical quantities such as the spin susceptibility and the electrical resistivity, both above and below $T_{\rm CO}$, 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-$T$ is determined by quantum Monte Carlo simulations. The results show that the spin susceptibility does not show a steep singularity at $T_{\rm CO}$, 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 $T_{\rm CO}$, below which a characteristic $T$ 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 Å3), 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 × 10−4 cm2 V−1 s−1. 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 (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

Tuning σ-Holes: Charge Redistribution in the Heavy (Group 14) Analogues of Simple and Mixed Halomethanes Can Impose Strong Propensities for Halogen Bonding

Halogen bonding between halide sites (in substituted organic molecules or inorganic halides) and Lewis bases is a rapidly progressing area of exploration. Investigations of this phenomenon have improved our understanding of weak intermolecular interactions and suggested new possibilities in supramolecular chemistry and crystal engineering. The capacity for halogen bonding is investigated at the MP2(full) level of theory for 100 compounds, including all 80 MH4-nXn systems (M = C, Si, Ge, Sn, and Pb; X = F, Cl, Br, and I). The charge redistribution in these molecules and the (in)stability of the σ-hole at X as a function of M and n are catalogued and examined. For the mixed MH3-mFmI compounds, we identify a complicated dependence of the relative halogen bond strengths on M and m. For m = 0, for example, the H3C-I----NH3 halogen bond is 6.6 times stronger than the H3Pb-I----NH3 bond. When m = 3, however, the F3Pb-I----NH3 bond is shorter and ∼1.6 times stronger than the F3C-I----NH3 bond. This substituent-induced reversal in the relative strengths of halogen bond energies is explained

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

La liaison halogène [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