E. I. Zhilyaeva

Electronic structure and electron-molecular vibrational coupling in organic superconductors ET4Hg2.89Br8 and ET2Cu(NCS)2: comparative studies by optical spectroscopy

Abstract Reflectance spectra of organic superconductors ET 4 Hg 2.89 Br 8 and ET 2 Cu(NCS) 2 are measured in the range from 650 to 40 000 cm −1 for different polarizations. The reflectance is analysed in the framework of the ‘phase phonons’ theory of M. J. Rice with the help of special transformation of the experimental data. Parameters of the electronic subsystem and of electron-molecular vibration coupling are determined. The role of anion-cation interaction is shown to be important for the onset of superconductivity.

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.

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.

Infrared spectra of conducting BEDSe-TTF charge-transfer salts with halide mercurate anions

Abstract We report on the studies of single crystal reflectance spectra (650–6500 cm −1 ) of four conducting radical cation salts formed by the organic donor, bis(ethylenediseleno) tetrathiafulvalene (BETSe-TTF) and mercury halide anions, Hg 3 Br 8 , HgBr 4 , Hg 2 I 6 and HgCl 4 . Additionally, infrared (IR) and Fourier transform near infrared (FT-NIR) Raman spectra of neutral BEDSe-TTF were measured. Electronic bands are analysed using a Drude–Lorentz dielectric function. Vibrational bands, mainly those related to the coupling of electrons with internal vibrations of BEDSe-TTF, are discussed. Considerable differences between IR spectra of the studied salts are mainly due to different charge of BEDSe-TTF cations.

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 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.

Onsager phase factor of quantum oscillations in the organic metal θ-(BEDT-TTF)4CoBr4(C6H4Cl2)

Abstract de Haas–van Alphen oscillations are studied for Fermi surfaces illustrating the Pippards model, commonly observed in multiband organic metals. Field- and temperature-dependent amplitude of the various Fourier components, linked to frequency combinations arising from magnetic breakdown between different bands, are considered. Emphasis is put on the Onsager phase factor of these components. It is demonstrated that, in addition to the usual Maslov index, field-dependent phase factors must be considered to precisely account for the data at high magnetic field. We present compelling evidence of the existence of such contributions for the organic metal θ -(BEDT-TTF) 4 CoBr 4 (C 6 H 4 Cl 2 ).

Synthesis and studies of new organic conductors based on ET and EDT-TTF with the [ZnBr4]2− anions

New layer organic conductors based on bis(ethylenedithio)tetrathiafulvalene (ET)4ZnBr4Solv (Solv stands for solvent) were synthesized in various halobenzenes as solvents (C6H5X, X = Cl, Br, F and C6H4Y2, Y = Cl, Br), as well as based on ethylenedithiotetrathiafulvalene (EDT-TTF)4MBr4(1,1,2-C2H3Cl3) (M = Zn, Mn) and (EDT-TTF)9(ZnBr4)2. The crystal structure of (ET)4ZnBr4(C6H4Cl2) at room temperature was established. It was found to be composed of alternating conducting layers with various structure of stacks formed of the ET radical cations. Their conductivity and ESR spectra were measured. The ET compounds obtained are organic metals up to the temperatures of 4.2, 72, 80, or 183 K (depending on the solvent: C6H4Cl2, C6H5Cl, C6H5Br, or C6H5F, respectively); the replacement of the solvent with more bulky 1,2-dibromobenzene led to the formation of a semiconductor. The compounds (EDT-TTF)4MBr4(C2H3Cl3) with M = Zn, Mn and (EDT-TTF)9(ZnBr4)2 retain metallic character of conductivity up to the temperatures of 260, 280, and 210 K.

Optical properties of a new organic metal (BEDO-TTF)5[CsHg(SCN)4]2

Abstract Polarized reflectance and optical conductivity spectra of single crystals of a new organic conductor based on the BEDO molecule, BEDO 5 [CsHg(SCN) 4 ] 2 , were investigated in the 600–6500 cm −1 and 9000–40 000 cm −1 range for the three principal axis at 300 K. Quasi-two-dimensional character of the conducting electronic system was established. The parameters of electronic system were obtained using the Drude model. The conducting bands of the investigated conductor appeared to be narrower than those of the recently investigated superconductor with the analogous structure, (BEDO-TTF) 2 ReO 4 (H 2 O). An assignment of the vibrational features for all the investigated polarizations was proposed.