S. A. Torunova

Phase transition at 320 K in a new layered organic metal conductor (BEDT-TTF)4CoBr4(C6H4Cl2)

A new layered organic conductor θ-(BEDT-TTF)4CoBr4(1,2-C6H4Cl2) with different resistivity behaviour that has metallic conducting layers and is semiconducting perpendicular to the layers has been prepared. A phase transition near 320 K was found in this salt by temperature variable resistivity and X-ray diffraction measurements. Precise crystal structure data, below transition (triclinic phase) and above transition (tetragonal phase), was determined. The crystal structures of both phases are composed of θ-type radical cation layers alternating with layers involving [CoBr4]2− anions and 1,2-dichlorobenzene molecules. The lower symmetry in the crystal structure of the triclinic phase is due to a non-symmetrical arrangement of the solvent molecules within the anion layers. In each structure, the neighbouring conducting layers of the unit cell differ in stacking directions. In the tetragonal phase, all conducting layers are similar in structure, and in the low-temperature triclinic phase, the neighbouring conducting layers differ in periods along the stacks (4.703 A and 4.993 A) and in dihedral angles θ between the BEDT-TTF radical cations of the adjacent stacks. The finding of compounds of the θ-(BEDT-TTF)4CoBr4(1,2-C6H4Cl2) type with phase transitions above room temperature provides a wide possibility of investigating magnetoresistance, quantum oscillations, and the mechanism of interlayer transport in layered conductors.

New organic metal (BEDO-TTF)4Pt(CN)4·H2O

Abstract A new charge transfer salt of (BEDO-TTF) 4 Pt(CN) 4 ·H 2 O (BEDO-TTF = bis(ethylenedioxo)tetrathiafulvalene) composition has been prepared. X-ray analysis shows that the conducting donor layers of new θ″-type packing alternate with anion sheets composed of [Pt(CN) 4 ] −2 anions, which are associated with H 2 O molecules via hydrogen bonds. Temperature and magnetic field dependences of the resistance are presented.

The preparation of (BEDO-TTF)2Cl·3H2O salt in Bu4NHgX3 + Bu4NX + 1,2-dichloroethane system. Shubnikov-de Haas oscillations

Abstract Electrochemical oxidation of BEDO-TTF (bis(ethylenedioxo)tetrathiafulvalene) in 1,2-dichloroethane in the presence of Bu 4 NHgX 3 + Bu 4 NX (X = I, Br, Cl) as a supporting electrolyte at low current density results in the isolation of (BEDO-TTF) 2 Cl · 3H 2 O salt. Its composition has been established by a chemical analysis (Cl, C, H), electron probe microanalysis and X-ray analysis. The temperature dependence of the resistance has been studied down to 1.5 K at a pressure up to 30 kbar and at room temperature up to 80 kbar. Field and angular dependences of magnetoresistance have been investigated.

BEDT-TTF, BEDO-TTF, and BEDSe-TTF salts with metal containing anions

Abstract The synthesis of new BEDO-TTF and BEDSe-TTF based salts with metal containing anions [HgX 3 ] − , [HgX 4 ] 2− , [Hg 3 X 8 ] 2− (X = Cl, Br, I), [Hg 3.5 I 9 ] 2− , [KHg(SCN) 4 ] − , [NH 4 Hg(SCN) 4 ] 2− , and [Pt(CN) 4 ] 2− is discussed. Most of the BEDO-TTF salts behave as metals down to 4 K. Among BEDSe-TTF salts only (BEDSe-TTF) 4 Hg 3 Br 8 TCE is a metal with the metal-insulator transition at 193 K.

New organic conductor (EDOEDT)4Hg3Br8 comprising cation layers of α″- and κ(4×4)-types

Abstract The (EDOEDT) 4 Hg 3 Br 8 radical cation salt of 4,5-ethylenedioxy-4′,5′-ethylendithiotetrathiafulvalene has been synthesized as a mixture of two crystalline phases. Phase 1 is characterized by a semiconducting type of conductivity and the ESR peak-to-peak linewidth equal to 70–95 G. Phase 2 exhibits metal-like conductivity down to 105 K and the ESR peak-to-peak linewidth of 35–54 G. The X-ray crystal structure analysis of phase 1 reveals three crystallographically distinct donor molecule layers in the asymmetric part of the unit cell, one of them being composed of the stacks and the two others are built of mutually perpendicular tetramers. The polarized reflectance spectra of phase 1 are discussed.

Radical cation salts of bis(ethylenediseleno)tetrathiafulvalene with halide mercurate anions

Abstract Four bis(ethylenediseleno) tetrathiafulvalene (BEDSe-TTF)-based salts, (BEDSe-TTF) 2 Hg 2 X 2 (X=I. Br), (BEDSe-TTF) 4 Hg 3 Br 8 · C 2 H 3 Cl 3 and (BEDSe-TTF) 4 Hg 3 Br 4 · 1.5C 2 H 3 Cl 3 , have been prepared by electrocrystallization. Two of them. (BEDSe-TTF) 2 Hg 2 X 6 , have been characterized by X-ray crystallography. The triclinic (space group P ī) room-temperature lattice parameters when X=I are: a = 6.798(4), b = 10.728(7), c 15.905(9) A, α=106.33(6)°, s=99.78(4)°, γ-92.97(5), V = 1090(1) A 3 . When X =Br the parameters are: a =6.665(3), b = 10.314(5), c =15.720(7) A, α-105.70(4)°, s=99.65(4)°, γ=93.79(4)°, V = 1018(1) A 3 . At room temperature, (BEDSe-TTF) 4 Hg 3 Br 8 · C 2 H 3 Cl 3 is metallic and the others are semiconductors.

Phase transitions in θ-(ET)4MnBr4(C6H6−nCln) (n = 1, 2) driven by ordering in anion and/or cation layers

Newly synthesized layered organic conductors θ-(ET)4MnBr4(1,2-C6H4Cl2) (1) and θ-(ET)4MnBr4(C6H5Cl) (2) show metal-like conductivity along conducting layers down to 4.3 and 60 K, respectively, while showing semiconducting properties in the perpendicular direction. Phase transitions driven by ordering in anion layers in 1 and ordering in a half of cation layers in 2 were found to occur at 297 and ~240 K, respectively. Crystal structures above and below the phase transitions were determined for 1 at 260 and 333 K and for 2 at 260 and 220 K. In the above-transition phases of both compounds, attributed to the tetragonal crystal system, all ET layers are similar in structure. In the below-transition phases, attributed to triclinic and monoclinic crystal systems, the neighboring ET layers of each phase differ in periods along the stacks and in dihedral angles θ between radical cations of the adjacent stacks.

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)3I0.5(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 γe, the energy shift Δ of the molecular orbital under the influence of the anions and vibronic coupling, the vibronic coupling constant gn, and the binding energy Ep 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.

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)4Hg3.5I9, and (BEDO-TTF)2HgBr3 possess the conductivity of the metallic type down to helium temperatures.

Evidence for a quantum dipole liquid state in an organic quasi–two-dimensional material

Quantum dipoles go liquid Quantum spin liquids do not achieve an ordered magnetic state, even at the lowest temperatures. Hassan et al. studied an organic compound that may be both a spin liquid and a dipole liquid (see the Perspective by Powell). In the layered material κ-(BEDT-TTF)2Hg(SCN)2Br, molecules form charged dimers whose sites are arranged on a triangular lattice. The extra charge associated with each dimer can “live” on one of the two molecules in the dimer, resulting in a nonzero electric dipole moment for the dimer. Raman spectroscopy and heat capacity measurements revealed that, like spins in a quantum spin liquid, these dimers remained disordered down to the lowest temperatures. Science, this issue p. 1101; see also p. 1073 Raman spectroscopy and heat capacity reveal the signatures of an exotic state in κ-(BEDT-TTF)2Hg(SCN)2Br. Mott insulators are commonly pictured with electrons localized on lattice sites, with their low-energy degrees of freedom involving spins only. Here, we observe emergent charge degrees of freedom in a molecule-based Mott insulator κ-(BEDT-TTF)2Hg(SCN)2Br, resulting in a quantum dipole liquid state. Electrons localized on molecular dimer lattice sites form electric dipoles that do not order at low temperatures and fluctuate with frequency detected experimentally in our Raman spectroscopy experiments. The heat capacity and Raman scattering response are consistent with a scenario in which the composite spin and electric dipole degrees of freedom remain fluctuating down to the lowest measured temperatures.