R. B. Lyubovskii

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.

A new series of ET-based organic metals: Synthesis, crystal structure and properties

Abstract New two-dimensional organic metals ET 2 [Hg(SCN) 3−n X n ], X=F, Cl, Br, I have been synthesized and investigated. ET 2 [Hg(SCN)Cl 2 ] and ET 2 [Hg(SCN) 2 X] (X=Cl, Br or (0,33 Cl+0, 66 Br) have been found isostructural. Cationic sheets of x -type alternate with anionic sheets. The [Hg(SCN) 3−n X n ] − (n=1,2) anions have a polymeric-structure and form chains with one or two SCN bridge ligands. The conductivity of salts with X=F is of a metallic character down to helium temperature, while all salts with X=Cl(n=1,2), (Cl 0,33 Br 0,66 ), Br exhibit metallic behaviour of their conductivity till 35, 50, 70 and 140 K, respectively, then they become insulators The salt with X=I is semiconductor.

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.

New BETS based molecular conductors with bromomercurate anions

Five BETS-based salts with different bromomercurate anions have been isolated. Some of these compounds ungergo the M-I transition with the temperature decrease, the others behave as metals. Among them a salt of nonstoichiometric composition BETS 4 Hg 2.84 Br 8 has been found with κ-type packing of organic layers.

Magnetic oscillations in a two-dimensional network of compensated electron and hole orbits

The Fermi surface of the quasi–two-dimensional (2D) organic metal (ET)8Hg4Cl12 (C6H5Br)2 can be regarded as a 2D network of compensated electron and hole orbits coupled by magnetic breakthrough. Simultaneous measurements of the interlayer magnetoresistance and magnetic torque have been performed for various directions of the magnetic field up to 28 T in the temperature range from 0.36 K to 4.2 K. Magnetoresistance and de Haas-van Alphen (dHvA) oscillations spectra exhibit frequency combinations typical of such a network. Even though some of the observed magnetoresistance oscillations cannot be interpreted on the basis of either conventional Shubnikov-de Haas oscillations or quantum interference, the temperature and magnetic field (both orientation and magnitude) dependence of all the Fourier components of the dHvA spectra can be consistently accounted for by the dHvA effect on the basis of the Lisfhitz-Kosevich formula. This behaviour is at variance with that currently reported for compounds illustrating the linear chain of coupled orbits model.

Competing types of quantum oscillations in the two-dimensional organic conductor ( B E D T − T T F ) 8 Hg 4 Cl 12 ( C 6 H 5 Cl ) 2

The interlayer magnetoconductance of the quasi-two-dimensional organic metal (BEDT-TTF) 8 Hg 4 Cl 1 2 (C 6 H 5 Cl) 2 has been investigated in pulsed magnetic fields extending up to 36 T and in the temperature range from 1.6 to15 K. A complex oscillatory spectrum, built on linear combinations of three basic frequencies only, is observed. These basic frequencies arise from the compensated closed hole and electron orbits and from the two orbits located in between. The field and temperature dependences of the amplitude of the various oscillation series are studied within the framework of the coupled-orbits model of Falicov and Stachowiak. This analysis reveals that these series result from the contribution of either the conventional Shubnikov-de Haas effect or quantum interference (QI), both of them being induced by magnetic breakthrough. Nevertheless, discrepancies between experimental and calculated parameters indicate that these phenomena alone cannot account for all of the data. Due to its low effective mass, one of the QI oscillation series-which corresponds to the whole first Brillouin zone area-is clearly observed up to 13 K.

Shubnikov-de Haas oscillations spectrum of the strongly correlated quasi-2D organic metal (ET)8[Hg4Cl12(C6H5Br)2] under pressure

AbstractPressure dependence of the Shubnikov-de Haas (SdH) oscillations spectra of the quasi-two dimensional organic metal (ET)8[ Hg4Cl12(C6H5Br)2] have been studied up to 1.1 GPa in pulsed magnetic fields of up to 54 T. According to band structure calculations, its Fermi surface can be regarded as a network of compensated orbits. The SdH spectra exhibit many Fourier components typical of such a network, most of them being forbidden in the framework of the semiclassical model. Their amplitude remains large in all the pressure range studied which likely rules out chemical potential oscillation as a dominant contribution to their origin, in agreement with recent calculations relevant to compensated Fermi liquids. In addition to a strong decrease of the magnetic breakdown field and effective masses, the latter being likely due to a reduction of the strength of electron correlations, a sizeable increase of the scattering rate is observed as the applied pressure increases. This latter point, which is at variance with data of most charge transfer salts is discussed in connection with pressure-induced features of the temperature dependence of the zero-field interlayer resistance.

New organic metals: BEDO-TTF bromomercurates

Electrochemical oxidation of BEDO-TTF (bis(ethylenedioxy)tetrathiafulvalene) in the presence of Bu 4 NHgBr 3 or Bu 4 NHgBr 3 + Bu 4 NBr as a supporting electrolyte in 1,2-dichloroethane (DCE) allows the isolation of (BEDO-TTF) 2 HgBr 3 , (BEDO-TTF) 5 Hg 1.9 Br 6.8 , (BEDO-TTF) 9 (HgBr 4 ) 2 .5DCE or (BEDO-TTF)Cl 0.5 .5H 2 O radical cation salts depending on conditions of electrochemical synthesis. Conditions for the synthesis, crystal structures and conductivity of the resulting BEDO-TTF bromomercurates are discussed.

The new salt κ-ET2[Hg(SCN)2I] : crystal structure and physical properties

Abstract The structure, resistivity and ESR of a new organic conductor κ-ET 2 [Hg(SCN) 2 I](ET=bis(ethylenedithio) tetrathiafulvalene) are studied. Its main crystallographic parameters are found to be: M -1213.2, a -38.03(1), b = 11.80(1), c = 8.329(9) A; γ=98.1(2)°; V -3700(2) A 3 ; space group P 2 1 Ib ; Z = 4. It is shown that the radical cations are packed according to the κ-type in the organic sheets, and the anions form polymerized chains. Two different radical cation layers with different amounts of shortened S···S contacts and distinct interaction between anionic and cationic sheets are found. ESR linewidth is found to be 9-11G (300 K), which is substantially narrower than a typical linewidth for ET-based radical cation salts of the κ-type. Based on temperature dependences of the resistance anisotropy and ESR parameters, we suggest that a structure rearrangement with electron localization may take place around 50 K. The comparison of crystal structure and properties of the title compound with other salts of the family ET 2 [Hg(SCN) 3 − n X n ], where X=Cl, Br, and n = 1.2, is camed out.

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.