Universität Stuttgart
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Item Open Access Plasma reflectance of the one-dimensional organic metals of the type (arene)2XF6(arene=perylene, pyrene or fluoranthene ; X=P, As, Sb)(1983) Geserich, Hans Peter; Koch, Bertram; Ruppel, Wolfgang; Wilckens, Rudolf; Schweitzer, Dieter; Enkelmann, Volker; Wegner, Gerhard; Wieners, Gerhard; Keller, Heimo J.We have investigated the spectral position and the form of the plasma edge of different radical cation salts of the type (arene)zXF, independence of the type of the organic donor molecule, and of the charge transfer between donor and acceptor molecules.Item Open Access Molecular solids containing BEDT-TTF and structurally related transition metal complexes(1986) Keller, Heimo J.; Niebl, Roland; Nöthe, Dietrich; Schweitzer, Dieter; Weber, AngelikaThe special physical properties of BEDT-TTF salts, e.g. their two-dimensional behaviour, are caused by the typical geometry of this donor and the arrangement of the cations in the crystal lattice of its salts. In order to extend the range of physical properties produced by BEDT-TTF like compounds, we synthesized sulfur containing transition metal complexes with a molecular structure very similar to BEDT-TTF. The bis(5.6-dihydro-1.4-dithin-2.3-dithiolate)metallates of the nickel triad can be prepared in different oxidation states as anions and in neutral form. The anionic complexes can be reacted with BEDT-TTF cations.Item Open Access The preparation of new metallic charge-transfer complexes: anthra [9.1-cd:10.5-c'd'] bis [1.2] dithiol (TTA), -diselenol (TSA) and their polyiodides(1982) Endres, Helmut; Keller, Heimo J.; Queckbörner, Jobst G.; Veigel, Jürgen; Schweitzer, DieterThe donors TTA and TSA were prepared starting from 1.5-dichloro-9.10-anthracenedione which was converted into 1.5.9.10-tetrachloroan-thracene (TCA) by two alternating chlorination and elimination steps. TCA was reacted under a dry argon atmosphere with suspensions of Na2S2 and Na2Se2 to yield TTA and TSA, respectively. Action of elemental iodine gives highly conductive polyiodides of both donors. Single crystals of TSA·I1.2 actually behave metallic between 220 and 300 K. The X-ray structure of TSA and TSA·I1.2 allows a comparison of intermolecular distances in the neutral and the partially oxidized, ionic stacks of the donor.Item Open Access Doped dialkylated phenazines : a novel series of highly conducting organic solids(1981) Dietz, Klaus; Flandrois, Serge; Keller, Heimo J.; Koch, P.; Queckbörner, Jobst G.; Schweitzer, DieterDoping dimethylphenazine (M2P)-TCNQ and diethylphenazine (E2P)-TCNQ with phenazine gave rise to new conducting compounds with segregated stacks : (M2P)0.5 (P)0,5 TCNQ and (E2P)0,55 (P)0,45 TCNQ. The room temperature electrical conductivities are in the range 10-100 Ω-1 cm-1 for (1) and 1-10 Ω-1cm-1 for (2). The paramagnetism of both compounds could be separated into contributions from TCNQ and Phenazine stacks. The structural electrical and magnetic similarities of (1) with the well-known N-methylphenazinium (NMP)-TCNQ led to a reexamination of its magnetic properties. It was shown that an estimate of the charge transfer can be obtained from the temperature dependence of the magnetic susceptibility.Item Open Access Magnetic susceptibility under pressure and anisotropy of electrical conductivity in quasi-one-dimensional (perylene)2(AsF 6)0.75(PF6)0.35 × 0.85CH2Cl2(1983) Moritz, I.; Shaheen, Salem A.; Hardebusch, U.; Schilling, James S.; Weger, Meir; Bender, Klaus; Schweitzer, Dieter; Keller, Heimo J.The magnetic susceptibility and electrical conductivity of the quasi-one-dimensional organic metal (Perylene)2(AsF6)0.75(PF6)0.35 × 0.85CH2Cl2 was studied in the temperature range 3–300 K. The measured susceptibility can be separated into its defect χd, core χc and enhanced paramagnetic spin susceptibility χp components. χp is found to decrease upon lowering the temperature or applying pressure, in analogy with results on charge transfer compounds such as TTF-TCNQ. The conductivity ratio σdouble vertical bar/σperpendicular also decreases with falling temperature. The present results are discussed within the context of a model which takes into account band-narrowing (electron localization) due to strong electron-phonon coupling.Item Open Access Electrochemical synthesis of new one-dimensional metals: radical salts of perylene(1981) Keller, Heimo J.; Nöthe, Dietrich; Pritzkow, Hans; Wehe, Dieter; Werner, M.; Harms, Ralf H.; Koch, P.; Schweitzer, DieterThe electrochemical synthesis of four highly conducting peryleniumyl salts is reported. The temperature dependence of the conductivity has been measured and exhibits a metallic regime between 200-300 K. The crystal structures of two of the compounds have been solved.Item Open Access Thermal expansion of the organic conductor β-(BEDT-TTF)2I3(1986) Hamzic, Bojana; Creuzet, Gerard; Schweitzer, Dieter; Keller, Heimo J.We report high resolution thermal expansion measurements between 1.2 and 300 K along the c*-axis in the organic conductor β-(BEDT-TTF)2I3 where the superconducting properties are strongly dependent on the way the system is prepared in the pressure-temperature diagram. We clearly observed a strong anomaly at 172 K related to the structural phase transition and the resistivity anomalies reported by several groups. The temperature analysis in the low temperature regime is coherent with a phonon dominant contribution. Finally, the presence of small hysteresis in a large region around the transitions seem to indicate why both the pressure and the temperature cycling may stabilize small regions of the high-Tc phase of the system, as observed.Item Open Access α- and β-(BEDT-TTF)2+I3-: two dimensional organic metals(1985) Hennig, Ingolf; Bender, Klaus; Schweitzer, Dieter; Dietz, Klaus; Endres, Helmut; Keller, Heimo J.; Gleitz, Arno; Helberg, Hans W.Electronic properties of α- and β-(BEDT-TTF)2I3 crystals are reported.Item Open Access Radical cation salts of BEDT-TTF and an unsymmetrical BEDT-TTF derivative(1986) Schweitzer, Dieter; Bender, Klaus; Endres, Helmut; Gärtner, Stephan; Heid, Rolf; Heinen, Ilsabe; Keller, Heimo J.; Weber, Angelika; Weger, MeirInvestigations of several BEDT-TTF and DIMET radical salts are presented. Measurements on β-(BEDT-TTF)2IAuI crystals show that their conducting and superconducting properties might vary strongly depending on the decomposition of (IAuI)− anions during the electrochemical process.Item Open Access Overhauser effect experiments on the one-dimensional conductor (perylene)2+PF6-·2/3THF(1984) Brunner, Hermann; Hausser, Karl H.; Keller, Heimo J.; Schweitzer, DieterWe have measured the Overhauser enhancement of the protons and the 19F-nuclei of the one-dimensional conductor (perylene)2+PF6-·2/3THF in its metallic phase at room temperature. The enhancement factor V was found to be VP=+320±20 for the protons and VF=+175±40 for the 19F-nuclei indicating a predominantly scalar interaction with the conduction electrons in both cases.