L.P. Rozenberg

Resistance and magnetoresistance anomaly in a new stable organic metal (ET)2TlHg(SCN)4

Abstract A new organic metal (ET) 2 TlHg(SCN) 4 has been synthesized. The X-ray study shows the compound to be isostructural to (ET) 2 MHg(SCN) 4 salts with M = K, NH 4 and Rb. The resistance and magnetoresistance measurements show anomalous behaviour at low temperature which may be attributed to spin-density-wave instability. Shubnikov-de Haas oscillations have also been observed at low temperature.

New cation-radical salts of BEDT-TTF with the octahedral metal complex anions PtCl62−, PtBr62−, TeCl62− and SnCl62−. Synthesis, structure and properties

Abstract A new series of isostructural cation-radical salts of bis(ethylene)dithiotetrathiafulvalene (BEDT-TTF) with the octahedral metal complex dianions PtCl62−, PtBr62−, TeCl62− and SnCl62− have been obtained. The crystal structure of the (BEDT-TTF)4PtCl6C6H5CN salt has been determined. Although it should be attributed to the k-type of BEDT-TTF metallic salts due to the packing arrangement of the BEDT-TTF molecules, it undergoes a first-order transition into the insulating state at 250 K. Application of a pressure higher than 6 kbar results in a new conducting state. The complexes of (BEDT-TTF) with the anions PtBr62−, TeCl62− and SnCl62− exhibit semiconducting properties.

The first ET salt with a metal complex anion containing a selenocyanate ligand, (ET)2TIlHg(SeCN)4 : synthesis, structure and properties

Synthesis of the first ET salt with a metal complex anion containing a selenocyanate ligand, α-(ET) 2 TlHg (SeCN) 4 , and its structure are reported. The temperature dependence of conductivity and thermopower in various crystallographic directions and the Shubnikov-de Haase oscillations have been studied. Distinctions of the bond length distributions in three crystallographically independent ET have been found, which may result in some charge localization in the radical-cation layer. A detailed comparison of the structure and properties of the compound obtained to its thiocyanate analog has been performed. It has been shown that in the α-(ET) 2 TlHg(SeCN) 4 salt there is no low-temperature phase transition characteristic of the α-(ET) 2 MHg(SCN) 4 compounds with M=K, Tl and Rb

Crystal structure and photoluminescence of single crystals of fullerene-9,9′-trans-bis(telluraxanthenyl) molecular complex: C26H18Te2 · C60 · CS2

Abstract The crystal structure of novel molecular complex of fullerene C60 with 9,9′-trans-bis(telluraxantheny):C26H18Te2 · C60 · CS2 (BTX · C60 · CS2) has been investigated by X-ray structural analysis. Its photoluminescence (PL) and optical reflectivity spectra have been examined. We have found that fullerene C60, donor BTX and carbon disulfide CS2 molecules are situated at the inversion centers (1,0, 1 2 ), ( 1 2 , 1 1 2 ,1), ( 1 2 , 1 2 ,1),( 1 2 , 1 2 , 1 2 ), respectively. The PL spectrum in C60+BTX is shifted by 0.16eV towards lower energies compared to C60. The optical reflectivity spectrum of C60 + BTX is also different from that of C60. The results are explained in terms of a decrease of the singlet exciton energy due to the strong interaction between C60 and BTX molecules. The decrease of PL intensity in the new complex has been found to begin at much lower temperature as compared to the pure C60 crystals.

New organic metal with the mixed anion, β-(ET)2(IBr2)0.7(I3)0.3: Synthesis, structure and properties

Abstract The crystals of the stable organic metal β-(ET)2(IBr2)0.7(I3)0.3 have been obtained by chemical oxidation of the concentrated solution of bis (ethylenedithio) tetrathiafulvalene by IBr in nitrobenzene. The total yield of the reaction is about 80%. The room-temperature conductivity of the single crystals in the conducting ab plane amounts to 10–50Ω−1 cm−1 and the ratio R293 K/R4 K = 300–400. The unit cell crystallographic parameters for β-(ET)2(IBr2)0.7(I3)0.3: a = 6.603(2), b = 8.996(2), c = 15.152(4) A, α = 94.05(2), β = 95.15(3), γ = 110.22(3)°, V = 836.2 A3 at 293 K and a = 6.608(2), b = 8.834(2), c = 15.038(3) A, α = 95.64(2), β = 95.01(2), γ = 109.91(2)°, V = 814.5 A3 at 130 K, space group P1¯, Z = 1. The orientation disordering of one of the ET ethylene groups (ET molecules are in staggered and eclipsed conformations) at room temperature, as well as complete ordering of the ones at 130 K (ET molecules are in eclipsed conformation only) was found. Differential scanning calorimetry (DSC) data show that order—disorder phase transition (ΔH=3.3 ± 0.1 J/g) takes place at 125–148 K.

A mixed κ-(ET)2Cu[N(CN)2]Br0.9I0.1 salt: synthesis, structure and superconductivity

Abstract Crystals of κ-(ET) 2 Cu[N(CN) 2 ]Br 0.9 I 0.1 (ET = bis(ethylenedithio)tetrathiafulvalene) salt have been prepared, and their structure and conducting properties have been studied. The crystals have been found to undergo a superconducting transition at 3.5 K ( T c ) when coated with Apiezon N grease to provide a very low pressure (about 0.3 kbar). With the application of quasihydrostatic pressure, the T c increases up to 5.9 K at about 3.0 kbar.

A new stable organic metal in the well known family of radical cation α-salts: α-(BETS)2TlHg(SeCN)4. Synthesis, structure and properties

The stable organic metalα-(BETS)2TlHg(SeCN)4 has been obtained by means of electrochemical oxidation of bis(ethylenedithio)tetraselenafulvalene (BETS) in 1,1,2-trichloroethane (TCE) with the addition of absolute ethanol in the presence of an electrolyte consisting of 18-crown-6, TlSeCN and Hg(SeCN)2 . The salt is isostructural with the ET-based salt with the same anion and ET and BETS salts with KHg(SCN)4 as well. The number of the side-by-side Se‥Se, Se‥S and S‥S contacts in each radical cation layer was twice that in comparison with the corresponding ET salt. Reflectivity spectra and magnetoresistance were studied. The Shubnikov–de Haas effect and angular oscillations of the magnetoresistance were observed. Optical and transport properties of α-(BETS)2TlHg(SeCN)4 were compared with those of the analogous ET salt.

Concerning the first-order phase transition in the low-dimensional organic superconductor (BEDO—TTF)2ReO4 · H2O. Crystal and electronic band structures below the phase transition (T = 170 K)

Abstract:The effect of the first-order phase transition occurring around 220 K on the crystal and electronic structure of the molecular superconductor (BEDO-TTF)2ReO4 · H2O has been studied. The crystal structure at 170 K has been determined and it is found that the main structural change resulting from the phase transition is connected with a rotation of the ReO4‒ anions. This rotation leads to changes in the S···S and S···O intermolecular contacts within the BEDO-TTF donor layers. How these structural changes affect the electronic structure of the salt is studied by comparing the transfer integrals for the different donor···donor intermolecular interactions calculated for the room temperature and 170 K crystal structures. It is shown that Fermi surfaces for the 170 K and room temperature structures are very similar, do not exhibit nesting properties, and can be described as resulting from the hybridization of superposing ellipses.

Different types of angular magnetoresistance oscillations in the low- and high-temperature states of the organic conductor (BEDTTTF)2KHg(SCN)4

Abstract Angular oscillations of semi-classical magnetoresistance of (BEDTTTF) 2 KHg(SCN) 4 have been studied at different temperatures under a magnetic field rotated in various planes perpendicular to the highly conducting ac -plane. At temperatures above the phase transition, T > T p ≈ 8 K , the oscillations are attributed to the electron motion along the closed orbits of the Fermi surface cylinder. In contrast, the low-temperature oscillations are found to be associated with the existence of a specific plane determined most likely by the wave vector of the superstructure arising below T p .

Pressure-effect and anisotropy of resistivity in organic metal (ET)2TlHg(SCN)4

Abstract A influence of quasi-hydrostatic pressure on the conducting properties of the organic metal (ET) 2 TlHg(SCN) 4 was investigated. The low-temperature anomaly (T 3 Kbar so that the high-temperature metallic state is stabilized down to 1.3 K. Temperature dependencies of the resistance were studied for different cristallographical directions. It was established that there is a correlation between the resistance anisotropy and the presumed shape of Fermi surface.