On the possibility of a radical decrease in the strength of many-body interactions in the organic metal α-(BETS)<Subscript>2</Subscript> KHg(SCN)<Subscript>4</Subscript>

Behavior of the de Haas-van Alphen (dHvA) oscillations depending on the angle between the magnetic field direction and the perpendicular to conducting layers in the quasi-two-dimensional organic metal α-(BETS)₂ KHg(SCN)₄ was studied in detail. The angular dependence of the dHvA oscillation amplitude exhibits a series of minima (at ±43.2°, ±64.6°, and ±72.0°) related to the “zero spin” effect, through which it is possible to estimate the splitting factor. An analysis of this value suggests that many-body interactions in the compound studied are either absent or at least radically weakened.     

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.     

Crystal structures of the organic metals (ET)2[Hg(SCN)Cl2] and (ET)2[Hg(SCN)2Br]

The compositions and structures of two new organic metals based on ET [where ET = bis(ethylenedithio)tetrathiafulvalene], viz., (ET)₂[Hg(SCN)Cl₂], with a metal-dielectric transition temperature (T_m-d) of 35°K, and (ET)₂[Hg(SCN)₂Br], with T_m-d = 140°K, were established by x-ray diffraction analysis. The crystal structures of the investigated compounds are similar to the structure of the previously studied organic metal (ET)₂[Hg(SCN)₂Cl] with T_m-d = 50°K. The principal crystallographic data for (ET)₂[Hg(SCN)Cl₂] are as follows: a = 36.64(1), b = 8.300(4), c = 11.798(1) Å, = 89.91(3)°, V = 3588.1(9) ų, space group Cc, Z = 4, d_calc = 2.05 g/cm³. The principal crystallographic data for (ET)₂[Hg(SCN)₂Br] are as follows: a = 37.088(14), b = 8.338(3), c = 11.738(5) Å, = 89.71(3)°, V = 3629.6(8) ų, space group C2/c, Z = 8, d_calc = 2.15 g/cm³. A characteristic feature of the crystal structure of the investigated compounds is alternation of the anion and cation layers along the a axis of the crystal. In the cation layer of the k type the ET are interconnected by shortened S...S intermolecular contacts (3.39–3.58 Å). The [Hg(SCN)_3–nX_n]^– anions (X = Cl, Br; n = 1, 2) form polymeric chains with one or two bridged SCN groups. A tendency for a decrease in the metal-dielectric transition temperature with a decrease in the volume of the anion is detected in the (ET)₂[Hg(SCN)_3–nX_n] salts, where X = Cl and Br, and n = 1 and 2.Institute of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2323–2331, October, 1992.     

De Haas-van Alphen oscillations in the organic quasi-two-dimensional metal (ET)<Subscript>8</Subscript>[Hg<Subscript>4</Subscript>Cl<Subscript>12</Subscript>(C<Subscript>6</Subscript>H<Subscript>5</Subscript>Cl)<Subscript>2</Subscript>]

The behavior of de Haas-van Alphen oscillations in the quasi-2D organic metal (ET)₈[Hg₄Cl₁₂(C₆H₅Cl)₂] was studied in detail. The section of the Fermi surface of this metal is a two-dimensional network of magnetic breakdown orbits. Only two frequencies, which corresponded to allowed closed orbits, F_A and F_MB, were detected. This is in agreement with the earlier studies of Shubnikov-de Haas oscillations in this metal. The reason for the absence of other allowed frequencies remains unclear. The angular dependences of the amplitudes of F_A and F_MB oscillations contain a series of “spin zeros.” An analysis of their positions led us to suggest that many-particle interactions were weakened in (ET)₈[Hg₄Cl₁₂(C₆H₅Cl)₂].     

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.     

New organic two-dimensional metals, (ET)4(Hg2X6)·PhCl (X=Cl,Br)

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2872–2873, December, 1990.     

Crystal structure, Fermi surface calculations and Shubnikov-de Haas oscillation spectrum of the organic metal θ-(BETS)4HgBr4(C6H5Cl) at low temperature

The organic metal θ-(BETS)₄HgBr₄(C₆H₅Cl) is known to undergo a phase transition as the temperature is lowered down to about 240 K. X-ray data obtained at 200 K indicate a corresponding modification of the crystal structure, the symmetry of which is lowered from quadratic to monoclinic. In addition, two different types of cation layers are observed in the unit cell. The Fermi surface (FS), which can be regarded as a network of compensated electron and hole orbits according to band structure calculations at room temperature, turns to a set of two alternating linear chains of orbits at low temperature. The field and temperature dependence of the Shubnikov-de Haas oscillation spectrum have been studied up to 54 T. Eight frequencies are observed which, in any case, point to an FS much more complex than predicted by band structure calculations at room temperature, even though some of the observed Fourier components might be ascribed to magnetic breakdown or frequency mixing. The obtained spectrum could result from either an interaction between the FSs linked to each of the two cation layers or to an eventual additional phase transition in the temperature range below 200 K.     

Quantum and semiclassical oscillations in the organic metal (BEDO-TTF)2Clx(H2O)y

We study quantum (Shubnikov-de Haas and de Haas-van Alphen) oscillations and angular oscillations of the reluctance in the organic quasi-two-dimensional metal (BO)₂Cl_x(H₂O)_y. We show that the Fermi surface in this compound consists of a slightly corrugated cylinder with its axis perpendicular to the conducting plane. The cross section of the cylinder in this plane is a perfect circle of radius k _F≃3×10⁷ cm⁻¹. The effective carrier mass associated with this cylinder is m*=(1.65–2.0) m ₀ in the conducting plane, while the Dingle temperature is T _D=3–4 K. Zh. éksp. Teor. Fiz. 114, 1137–1146 (September 1998)     

Shubnikov-de Haas oscillations in a new dual-layered quasi-two-dimensional organic metal (BETS)4CoBr4(C6H4Cl2)

The interlayer and intralayer resistances and Shubnikov-de Haas oscillations in a new dual-layered quasi-two-dimensional organic metal (BETS)₄CoBr₄(C₆H₄Cl₂) with a periodically varying structure of cation layers have been studied. It has been shown that the interlayer resistivity corresponds to an incoherent or weakly incoherent transport regime. The oscillations of the magnetoresistance have been described by a model of a chain of coherent magnetic breakdown orbits taking into account the quantum interference effect. The behavior of the interlayer transport, as well as quantum oscillations, is in good agreement with the theoretical calculations of the band structure.