New organic metals: Radical cation salts of bis(ethylenedioxo)tetrathiafulvalene with halide mercurate anions

Radical cation salts with halide mercurate anions were obtained by the electrochemical oxidation of bis(ethylenedioxo)tetrathiafulvalene (BEDO-TTF), and their conductivity was studied. The compounds (BEDO-TTF)₄Hg₃X₈ (X = Cl or Br), (BEDO-TTF)₄Hg_3.5I₉, and (BEDO-TTF)₂HgBr₃ possess the conductivity of the metallic type down to helium temperatures.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1167–1170, May, 1996.     

Optical Study of Anisotropy in Organic Conductors D4[MBr4](Solvent)

Russian Journal of Physical Chemistry A - The polarized reflectance and optical conductivity spectra of layered organic conductors D4[MBr4](Solvent): θ-(BEDT-TTF)4HgBr4(DCB),...     

Molecular conductors with differently oriented conducting layers, (EDT-TTF)3Hg2Br6 and (TMBEDT-TTF)5Hg(SCN)4-xIx

New conducting radical cation salts (EDT-TTF)₃Hg ₂Br6, (TMET) ₅Hg(SCN) _4-xI_x (x≈0.35), and (EDT-TTF)₃Hg(SCN)₃I_0.5(PhCl)_0.5 were synthesized. Their conductivities, ESR and polarized reflectance spectra were studied. It was shown that the organic conductors with differently oriented conducting layers (EDT-TTF)₃Hg₂Br₆ and (TMET)₅Hg(SCN)_4-xI_x (x≈?0.35) are characterized by the quasi-one-dimensional character of electron motion. The conductivity along and across conducting layers has a semiconductive character. It was established by ESR and polarized reflectance spectroscopy that the properties of such conductors are a superposition of the properties of individual conducting layers.     

Effect of the quality of crystalline samples on the interlayer electron transport in the organic quasi-two-dimensional metal (ET)8Hg4Cl12(C6H5Cl)2

The behavior of magnetoresistance is studied in two samples of the quasi-two-dimensional organic metal (ET)₈Hg₄Cl₁₂(C₆H₅Cl)₂ having different quality for various magnetic field directions. The interlayer transport in the high-quality sample is shown to be close to a coherent mode, and the interlayer transport in the low-quality sample is closer to an incoherent mode.     

Charge Transfer between Layers in a Bilayer Quasi-Two-Dimensional (BEDT-TTF)4CoBr4(C6H4Cl2) Organic Metal

Journal of Experimental and Theoretical Physics - Based on the analysis of the behavior of the magnetoresistance, the regime of interlayer charge transport in a bilayer quasi-two-dimensional...     

Optical investigations of anisotropy of the conducting π-electron system in crystals of the organic superconductor (EDT-TTF)4[Hg3I8]1 − x

The polarized reflectance spectra of microcrystals of the new organic superconductor (EDT-TTF)₄[Hg₃I₈]_{1 ? x} (T _c = 8.1 K for x = 0.027; T _c = 7 K at 0.3 kbar for x = 0.019) have been investigated in the spectral region of 700–6000 cm^?1 (0.087–0.740 eV) at temperatures ranging from 10 to 300 K. A quantitative analysis of the spectra has been performed in the framework of the phenomenological Drude and Drude-Lorentz dispersion models, as well as in the framework of the theoretical “phase phonon” model that takes into account the interaction of free electrons with intramolecular vibrations. The effective mass of charge carriers m*, the width of the initial metallic π-electron band W, and the integral t of the electron transfer between the molecular π-orbitals of neighboring molecules have been determined. In the low-frequency range (700–1600 cm^?1), the vibrational structure associated with intramolecular vibrations of the EDT-TTF molecule has been revealed. It has been shown that the most intense feature (ω = 1330 cm^?1) of this structure is caused by the interaction of “quasi-free” electrons with intramolecular vibrations.     

Optical properties of low-dimensional organic conductors with differently oriented conducting layers: (EDT-TTF)3Hg2Br6 and (EDT-TTF)3Hg(SCN)3I0.5(PhCl)0.5

Spectral optical investigations of two low-dimensional organic molecular conductors with differently oriented conducting layers of ethylenedithiotetrathiafulvalene (EDT-TTF) molecules, namely, the (EDT-TTF)₃Hg₂Br₆ and (EDT-TTF)₃Hg(SCN)₃I_0.5(PhCl)_0.5 single crystals, have been carried out. The polarized reflectance spectra of the single crystals have been measured in the frequency range 700–6500 cm⁻¹ (0.087–0.810 eV) at temperatures from 300 to 15 K. The optical conductivity spectra have been obtained using the Kramers-Kronig relations, and their quantitative analysis has been performed in terms of a theoretical model that takes into account electron-electron correlations in the approximation of the Hubbard Hamiltonian for trimerized stacks, the vibronic coupling, and the influence of the counterion on the electronic states in the trimer. A satisfactory agreement between the theoretical and experimental spectra for both crystals made it possible to estimate the parameters of the electronic structure of the crystals in the conducting plane: the integral t of the electron transfer between the EDT-TTF molecules in the trimer, the energy U of the Coulomb repulsion between two electrons (holes) in one EDT-TTF molecule, the electron transfer damping constant γ _e , the energy shift Δ of the molecular orbital under the influence of the anions and vibronic coupling, the vibronic coupling constant g _n , and the binding energy E _p of the molecular polaron. It has been found that there are large differences in the anisotropies of the optical properties and the obtained Hubbard parameters of the electronic structure for the studied crystals.

     

Hydrostatic-Pressure-Induced Reentrance of the Metallic State in the κ-(ET)2Hg(SCN)2Cl Quasi-Two-Dimensional Organic Conductor

On cooling below 30 K, the κ-(ET)₂Hg(SCN)₂Cl quasi-two-dimensional organic metal, which is in the quantum spin liquid state at liquid helium temperatures, undergoes a transition to the Mott insulator state. The application of a hydrostatic pressure p = 0.7 kbar stabilizes the metallic state and makes it possible to study the behavior of the interlayer magnetoresistance at liquid helium temperatures. The field dependence of the magnetoresistance exhibits an unlimited power-law growth, which indicates that the polaron mechanism contributes to the interlayer transport. The spectrum of observed magnetoresistance oscillations corresponds to the Fermi surfaces characteristic of conducting layers with the κ-type structure.

     

Tetrathiafulvalene-based organic conductors with Pb-containing anions

Hybrid compounds containing organic layers composed of tetrathiafulvalenes (BEDT-TTF, BETS, BEDO-TTF) and inorganic layers consisting of anions based on lead bromide were synthesized. The crystal structure of (BEDT-TTF)₆Pb₃Br₁₀(PhBr) was determined. The temperature dependences of electrical conductivity for the synthesized compounds were measured and the EPR spectra of these compounds were recorded. In the structure of (BEDT-TTF)₆Pb₃Br₁₀(PhBr), the organic conducting layers of BEDT-TTF molecules alternate with non-conducting layers composed of infinite chains of bromoplumbate anions [Pb₃Br₉]^3–, solvent molecules, and Br^– anions. The newly synthesized BEDT-TTF bromoplumbates have similar linewidths of EPR signals, which indicate that their conducting layers have similar structures. The BEDT-TTF bromoplumbates are semiconductors, while temperature-dependent electrical resistivity measurements show the metallic behavior for BEDO-TTF and BETS bromoplumbates.     

Organic conductors with BiIII and SbIII chloride-based anions

New layered organic conductors, (BEDT-TTF)4(BiCl5)1 7 (1), δ-(BEDT-TTF)2BiCl5 (2), and δ-(BEDT-TTF)6Sb3Cl12 (3), were obtained (BEDT-TTF is bis(ethylenedithio)tetrathia-fulvalene). In the crystal structures of 1—3, organic radical cation layers are composed of di-merized stacks. The dimers are formed by BEDT-TTF radical cations rotated through angle ω relative to each other, which results in twisted stacks, giving rise to so-called twisted overlap mode in the layers. These layers alternate with non-conductive inorganic layers consisting of chains in which the Cl, Bi, and Sb sites are partially occupied. This indicates discontinuities in the chains of anions, and, apparently, the absence of continuous polymer chains in the crystal structure. According to measurements of the temperature dependence of the electrical resistance, the compounds are semiconductors.