Ingolf Hennig

Synthesis, Structure and Physical Properties of a Two-Dimensional Organic Metal, Di[bis(ethylenedithiolo)tetrathiofulvalene] triiodide, (BEDT-TTF)+ 2 I− 3

Abstract Electrical oxidation of bis(ethylenedithiolo)tetrathiofulvalene (BEDT-TTF) 1 in a nitrogen saturated tetrahydrofurane solution containing (n-C4H10)4N+I3 as electrolyte results in the deposition of crystal plates of (BEDT-TTF)+ 2I3 (C10H8S8)2I3. These two dimensional crystals are triclinic, space group P1, a = 9.211(2), b=10.850(4), c = 17.488(5) A, α=96.95(2), β = 97.97(2), γ = 90.75(2)°, V = 1717 A3, Mr = 1150.01, Z=2, Dx =2.22 g cm−3. Rw = 0.037 for 2462 observed reflections. Sheets of alternating cations and anions occur in the compound. The most prominent intermolecular S-S contacts (∼3.5A) are found between the stacks of BEDT-TTF. The stacking of the molecules and the interstack contacts give the compound a two-dimensional character which influences the physical properties. The room temperature conductivities in the ab plane range typically between 60 and 250 (ω cm)−1. The conductivity anisotropy in this plane is small with a ratio of σa/σb⩽ 2, while in the direction perpendicular to the ab-...

(BEDT-TTF)+ 2J- 3: A Two-Dimensional Organic Metal

Abstract Temperature - dependent thermopower-, dc- and microwave conductivity meaurements on the two-dimensional organic metal (BEDT-TTF)+ 2J- 3 are reported.

Electric conductivity and thermoelectric power of various polypyrroles

The dc-conductivity and thermoelectric pover of electrochemically prepared polypyrroles have been investigated in the temperature range between 300 K and 1.3 K on unaged. aged ( 2~-120 days at 80 0 c in air) and chemically modified samples. The linear temperature dependence of the thermopower of unaged polypyrroles demonstrates clearly the contribution of metallic regions to the electronic transport properties. The temperature dependence of the conductivity ot the polypyrroles investigated corresponds to that predicted by the variable range hopping model.

Superconductivity at ambient pressure in BEDT-TTF radical salts

Abstract Crystals of (BEDT-TTF)2Cu(NCS)2 were prepared by several methods and the super-conducting transitions investigated by resistivity and ac susceptibility measurements. Depending on the preparation of the crystals a variation of the temperature of the superconducting transition is observed. This variation is manifested in the upper critical fields Hc2 and proton NMR relaxation measurements at temperatures below TC show it as well. The upper critical fields HC2 of crystals of αt-(BEDT-TTF)2I3 were determined in dependence of the temperature and of the direction of the magnetic field with respect to the various crystal axes by measuring the mid transition of the resistivity and of the rf penetration depth. The data are analyzed with the anisotropic effective mass model in the picture of the Ginsburg Landau (GL) theory as well as in the picture of a layered superconductor. 13C Knight shifts by magic angle sample spinning and NMR cross polarisation methods support the picture of the layered superconductor.

Organic Metals from Simple Aromatic Hydrocarbons: Perylene Radical Salts

Crystal structures, temperature dependent thermopower and conductivity measurements of several metallic perylene radical salt phases are discussed.

TCNQ SALTS OF PLANAR METAL COMPLEX CATIONS: NOVEL MOLECULAR CONDUCTORS AND SEMICONDUCTORS.

Abstract The facile variation of positive charge of oxamide oxime metal complexes, caused by acid-base equilibrium, allows the growth of single crystals of their TCNQ salts. 1:1 salts consist of reqular segregated stacks of the components, with metallic room temperature behaviour of the Ni compound, the Pt compound being a semiconductor. Room temperature conductivities are of the order of 10 Siemens per cm. A 2:3 Pt complex TCNQ salt contains segregated acceptor stacks with half a negative charge per molecule. These stacks run perpendicular to mixed stacks -D-D-A-D-D-A-, with integral charges on donors D and acceptors A.

NMR investigations of the organic metals and superconductors α-(BEDT-TTF)2I3, ß-(BEDT-TTF)2I3 and αt-(BEDT-TTF)2I3

Abstract 1 H and 13 C spin lattice relaxation rates as well as 13 C Knight shifts of the quasi two dimensional organic metals α-, β- and α t -(BEDT-TTF) 2 I 3 are reported. In β- and α t -(BEDT-TTF) 2 I 3 at temperatures below 100 K the Korringa relation is fulfilled. Near the critical temperature of 8K of the stable superconducting state of α t -(BEDT-TTF) 2 I 3 an enhancement of the proton spin lattice relaxation rate due to superconducting fluctuations is observed. The observed individual 13 C Knight shifts, as measured by magic angle sample spinning and cross polarisation methods range between -6 and +244 ppm for α- phase and -10 and +125 ppm for β- and α t - phase crystals.