Lydie Valade

Pressure-temperature phase diagram of α′-TTF [Pd(Dmit)2]2

Abstract Temperature dependence of resistivity (up to 24 Kbar) and of E.S.R. (at 1 bar) measurements suggest that centered monoclinic TTF[Pd(Dmit) 2 ] 2 could be an anisotropic and weak antiferromagnetic fluctuating metal. At low pressure, gradual charge and spin localizations at different temperatures are the signature of a Mott-Hubbard insulator. Above 20 Kbar, “high” superconducting onset temperatures (6.5 K) are observed.

A facile route for the preparation of nanoparticles of the spin-crossover complex [Fe(Htrz)2(trz)](BF4) in xerogel transparent composite films

Films and monoliths containing the spin crossover complex [Fe(Htrz)(2)(trz)](BF(4)) (trz = 1,2,4-triazole) as nanoparticles have been obtained. The dispersion and consecutive inclusion of the Fe complex in a silica matrix prepared from tetramethoxysilane or tetraethoxysilane afford monoliths or films with a violet colour at room temperature, which turns white above 380 K. This change of colour is reversible. This thermochromic behaviour has been characterized by measuring the magnetic properties together with thermogravimetric studies and Raman spectroscopy, the result of which all demonstrate that both films and monoliths undergo a spin crossover. Microscopy studies confirm the occurrence of the Fe complex as nanoparticles, in both the monoliths and the films. The facile synthesis of these materials as nanoparticles in transparent films should open the possibility of the synthesis of high quality films.

Structural Evidence of Charge Density Waves in the Series of Molecular Conductors and Superconductors: TTF(M(dmit)2)2 (M = Pd, Ni)

We present an x-ray study at ambient pressure of the metal complexes TTF(Pd(dmit)2)2 and TTF(Ni(dmit)2)2 as a function of temperature. At room temperature one-dimensional (1D) fluctuations are observed under the form of diffuse lines on the x-ray patterns. The Ni-derivative exhibits one type of scattering which condenses below about 40 K into satellite reflections. The Pd-derivative shows two kinds of scattering which condense into satellite reflections, respectively, at T1 ≈ 150 K and T2 ≈ 105 K. These observations provide evidence of charge density wave instabilities related to the 1D electronic anisotropy of these materials, and which compete with superconductivity under pressure.

Nanowires of molecule-based charge-transfer salts

Nanowires of molecule-based charge-transfer salts are prepared using two different processing techniques. Isolated [TTF][TCNQ] nanowires are grown by a simple adsorption in organic solution method on stainless steel conversion coatings, used as substrates. They are characterized by Raman spectroscopy and current–voltage measurements. Nanowire films of Per2[Au(mnt)2] and (EDT-TTFVO)4(FeCl4)2 are electrodeposited on (001)-oriented silicon wafers, used as anodes. In the second case, growth as nanowires occurs after functionalizing the Si electrode with a phospholipidic membrane. Electrodeposited nanowire films are studied by various techniques, including electron microscopy, vibrational spectroscopies, X-ray photoelectron spectroscopy and conductivity measurements.

Polymorphism and its effects on the magnetic behaviour of the [Fe(sal2-trien)][Ni(dmit)2] spin-crossover complex

The syntheses, structural characterisation, and magnetic and spectroscopic properties of three new polymorphs of the spin-crossover complex [Fe(sal2-trien)][Ni(dmit)2] are reported. The results are discussed as a function of their intra- and intermolecular arrangement. Correlation of their crystal structures and magnetic properties suggest that some torsion angles play a significant role in the magnetic properties of this class of compounds. Intermolecular contacts are also of importance, and the nature of the short contacts between molecular species seems to be more crucial than their number in the allowance of spin-crossover.

Synthesis, Electrical Conductivity, and Crystal Structure of (AsPh4)0.25 [Ni(dmit)2]

Abstract The synthesis, conductivity behavior and crystal structure of the ion radical salt (AsPh4)0.25 [Ni(dmit)2] are described. This compound crystallizes in the monoclinic system, space group Pn or P2/n, a = 13.507(7), b = 6.610(1), c = 44.536(7) A, β = 96.08(2)[ddot]. The structure consists of thick layers of stacked Ni(dmit)2 entities parallel to (001) and separated by AsPh4 + cations. Short S… S interstack distances are observed such that two-dimensional networks of closely spaced Ni(dmit)2 are formed in the (001) plane of this structure. The two-dimensional character of the structure is reflected in the low anisotropy in the conductivities measured in the (001) plane (σ = 1 : 1 : 10−3. The room-temperature four-probe conductivities measured along the needle axis (b axis) is 10-15 ω−1 cm−1. Temperature-dependent measurements show a thermally activated conductivity with very low activation energies (ca. 0-0.01 eV).

Effect of pressure on the superconducting transition temperature of tetrathiofulvalene bis-[bis-(4, 5-dimercapto-1, 3-dithiol-2-thione) nickel (II)] (TTF[Ni(DMIT)2]2)

Abstract The effect of pressure on the superconducting transition temperature of TTF[Ni(dmit) 2 ] 2 is determined. This is the first organic superconductor in which the transition temperature increases with increasing pressure.

Nanoparticles of organic conductors: synthesis and application as electrode material in organic field effect transistors

Stabilization of TTF·TCNQ nanoparticles is studied by varying the ionic liquid nature and solvent medium. The best dispersion is obtained in an acetonitrile/acetone mixture and the smaller size by using [BMIM][BF4], as a stabilizing ionic liquid. Applications of well-dispersed TTF·TCNQ nanoparticles (mean diameter of about 35 nm) as electrode material in organic field-effect transistors are also reported.

NMR Analysis of Spin Fluctuations in the Organic Conductor TTF[Ni(dmit)2]2

We present and analyse 1H NMR relaxation (T1-1) data of the two-chain organic conductor TTF [Ni(dmit)2]2 as a function of temperature and magnetic field at ambient pressure. In the entire temperature domain studied between 1 and 300 K, we report important deviations to the normal metal Korringa law. We show that both T1 temperature and field dependences can be well understood in terms of a typical balance between 1D uniform field-dependent and diffusive spin correlations, which dominate the relaxation enhancement above 60 K or so, and 1D antiferromagnetic fluctuations that strongly develop below this temperature with a power law temperature dependence. The successful comparison between theory and experiment strongly supports a model in which TTF-conducting chains are dominated by repulsive electron-electron interactions and 1D correlation effects down to the lowest temperature reached.

From molecule-based (super)conductors to thin films, nanowires and nanorings

Thin films of (TTF)(TCNQ) (TTF=tetrathiafulvalene, TCNQ=tetracyanoquinodimethane) are deposited on Si (001), KBr, and stainless steel conversion coatings (SSCC) using chemical vapor deposition. These films are characterized by IR, XRD, conductivity measurements, and SEM. Conducting nanowires and nanorings of (TTF)(TCNQ) and nanowires of (TTF)[Ni(dmit) 2 ] 2 (typically, 20 nm×20 μm) are prepared by successively dipping SSCC in acetonitrile solutions of TTF and TCNQ, or (TTF) 3 (BF 4 ) and (Bu 4 N)[Ni(dmit) 2 ], respectively. These nanowires are observed by SEM. The (TTF)(TCNQ) nanowires are also observed by TEM and AFM and characterized by current-voltage measurements. Nanowires of (TTF)[Ni(dmit) 2 ] 2 are also obtained on silicon conversion coatings (SiCC) and characterized by Raman spectroscopy.