Universität Stuttgart
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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 1,3,5-Tris(dimethylamino)benzol mit Iod und 1,3,5-Tricyanobenzol : eine ungewöhnliche Dimerisierung und ein "normaler" Donor/Akzeptor-Komplex(1988) Keller, Heimo J.; Niebl, Roland; Renner, Gerd; Ruhr, Dorothea von der; Schweitzer, DieterWir sind auf der Suche nach "organischen" Ferromagneten. Als Zielsubstanz haben wir kristallisierte Radikal-Ionen mit bahnentarteten Grundzuständen ausgewählt. Molekulare Festkörper aus planaren organischen Radikalionen zeigen ein breites Spektrum teilweise recht interessanter physikalischer Eigenschaften, die durch kollektives Elektronenverhalten zu erklären sind. In den letzten Jahren wurde vor allem das elektrische Verhalten dieser Substanzen untersucht. Dies führte zur Entdeckung einer Vielzahl "organischer Metalle", von denen einige bei tiefer Temperatur auch supraleitend werden.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 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 New charge tranfer salts containing BEDT-TTF and structurally related transition metal complexes(1987) Keller, Heimo J.; Niebl, Roland; Nöthe, Dietrich; Schweitzer, Dieter; Weber, AngelikaThe two-dimensional behaviour of BEDT-TTF salts is normally explained with the typical geometry of this donor and its arrangement in the crystal lattice. In order to extend the range of physical properties produced by BEDT-TIF 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-dithiin-2,3-dithiolate)metallates of the nickel triad can be prepared in different oxidation states as anions and in a fully oxidized neutral form.Item Open Access Two superconducting phases in the organic conductor: β-(BEDT-TTF)2I3(1986) Creuzet, Francois; Bourbonnais, Claude; Creuzet, Gerard; Jerome, Denis; Schweitzer, Dieter; Keller, Heimo J.We have investigated the nature and the stability of the high-Tc(∼8 K) and low-Tc (∼1.5 K)superconducting phases (respectively called β-H and β-L) of the organic conductor β-(BEDT-TTF)2I3. First, by resistivity measurements and following a well-defined temperature-pressure cycling process, we show that the β-H phase is stabilized at ambient pressure and low temperature, exhibiting a very sharp and complete superconducting transition at 8.1 K and 1 bar. Secondly, an AC-susceptibility study reveals that this state is stable and exhibits bulk superconductivity at high Tc and ambient P as long as the sample is not warmed above 125 K. Finally, we present NMR results on the 1H spin-lattice relaxation rate behaviour in both the β-H phase and the β-L phase.Item Open Access The high-Tc superconducting state of β-(BEDT-TTF)2I3 at atmospheric pressure: bulk superconductivity and metastability(1986) Creuzet, Francois; Jerome, Denis; Schweitzer, Dieter; Keller, Heimo J.The AC susceptibility study of β-(BEDT-TTF)2I3 reveals that the high-Tc metastable superconducting state which can be stabilized at atmospheric pressure after a particular pressure-temperature cycling procedure, exhibits bulk superconductivity resembling very closely that of the high-Tc state, which is stabilized above 1 kbar. Annealing experiments show that the high-Tc state remains stable at low temperature as long as the annealing temperature does not exceed 125 K.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 Electrocrystallization and structures of perylene radical salts: hexaperylene perchlorate, (C20H12)6+ClO4-, triperylene perchlorate, (C20H12)3+ClO4-, and diperylene hexafluorophosphate-tetrahydrofuran (3/2), (C20H12)2+PF6-.2/3C4H8O(1985) Endres, Helmut; Keller, Heimo J.; Müller, Barbara; Schweitzer, DieterCrystals grown by electrocrystallization, species obtained depending on perylene concentration. Room-temperature data collect ions, Mo Kat λ = 0·71069 A. 6:1 salt: Mr= 1613·3, triclinic. pl, a = 12·57 1 (7), b = 13·699(5). c = 13.835(II)A, α = 110·43 (4), β= 107·13 (7), γ= 107·09 (4)°, V = 1913A3, Z = 1, Dx = 1.40gcm-3, μ= 1.1 cm- ', F(OOO) = 841, final R = 0·077 for 3171 observed reflections. The structure contains three independent perylene π dimers arranged nearly perpendicularly to each other. The anions are severely disordered or freely rotating. 3:1 salt: Mr = 856·4, triclinic, PI, a = 13·009(8), b= 13.821 (10), c= 13·850(15)A, α = 66·05(7), β = 83·36 (8). γ= 63·5 1 (6)°, V = 2030A3, Z = 2, Dx= 1.40gcm-3 , μ= 1·5cm-1 , F(OOO) = 890, final R = 0· 138 for 3523 observed reflections. Tetrameric perylene stacks are surrounded on four sides by single perylene species, having their planes nearly perpendicular to the molecular planes in the stacks. 2:1 salt: Mr = 697· 7, monoclinic, P2/m, a = 13·04(1), b = 14 · 12 (1), c = 13·75 (1)A, β=110·80 (2)°, V = 2367 A3, Z = 3, Dx = 1·47 g cm-3',μ= 1·5 cm- ', F(OOO) = 1079, final R =0· 121 for 1737 observed reflections. Nearly regular perylene stacks are surrounded by single perylene species in a way similar to the 3:1 salt. The thf solvent and one of the perylene molecules are disordered over two orientations.