Universität Stuttgart

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Subject: search.filters.subject.530Author: search.filters.author.Schweitzer, DieterInstitute: search.filters.UBSInstitut.Sonstige EinrichtungStart date: 1987End date: 1987

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Now showing 1 - 10 of 26
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    Structures of 3,6-dimethoxy-1,2,4,5-tetrazine(V) and 3,6-Bis(1-aziridinyl)-1,2,4,5-tetrazine(VI)
    (1987) Krieger, Claus; Fischer, Hans; Neugebauer, Franz A.; Gückel, Friedemann; Schweitzer, Dieter
    (V): C4H6N4O2, Mr=142·12, orthorhombic, Pbca, a=6·865(3), b =13·192(5), c=7·013(3)A, V =635·1(7)A3, Z=4, Dx=1·486gcm-3, λ(MoKα)=0·71069A, μ=1·139cm-1, F(000)=296, T=295K, R=0·043 for 589 unique observed reflections [I ≥ 1·96σ(I)]. (VI): C6H8N6, Mr=164·18, monoclinic, C2/m, a=9·660(2), b=9·077(1), c=4·294(1)A, β=91·07(I)°, V=376·5(2)A3, Z=2, Dx=1·448gcm-3, λ(MoKα)=0·71069 A, μ=0·952 cm-1, F(000)=172, T=295K, R=0·037 for 405 unique observed reflections [I≥1·96σ(I)]. (V) and (VI) are centrosymmetric, with planar 1,2,4,5-tetrazine rings slightly compressed in the C···C direction (N-C-N≅126°). The remarkably short exocyclic C-O [1·328(2)A] and C-N[1·385(1)A] bond distances indicate that the methoxy and aziridinyl substituents act as π donors to the electron-deficient 1,2,4,5-tetrazine system.
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    Metallic coordination polymers using CS2 as starting material
    (1987) Keller, Heimo J.; Klutz, Thomas; Münstedt, Helmut; Renner, Gerd; Schweitzer, Dieter
    Organic polymers with "metallic" properties have found widespread interest during the last few years. Acetylene and aniline as well as different nitrogen and sulfur heterocycles have been used as starting materials. One main problem hampering the technical application of these solids up to now is their environmental and thermal instability. Therefore, we introduced metal ions to stabilize polymeric backbones with high electrical conductivity. Because of the enormous coordination ability of sulfur to many transition metal ions we decided to use a polymeric carbon-sulfur backbone.
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    New charge tranfer salts containing BEDT-TTF and structurally related transition metal complexes
    (1987) Keller, Heimo J.; Niebl, Roland; Nöthe, Dietrich; Schweitzer, Dieter; Weber, Angelika
    The 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.
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    BEDT-TTF radical salts: organic metals and superconductors
    (1987) Schweitzer, Dieter
    A review of the structural, electronic and superconducting properties of some BEDT-TTF-radical salts is given.
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    The effect of disorder on the conduction electron spin resonance linewidth of the α and β phases of (BEDT-TTF)2I3
    (1987) Forró, Laszlo; Schweitzer, Dieter; Keller, Heimo J.
    We present the electron spin resonance linewidth of α and β phases of the organic conductor di-bis (ethylenedithiolo) tetrathiafulvalene driiodide [(BEDT-TTF)2I3] disordered by fast electron irradiation. In the high temperature metallic phase the linewidth decreases in both phases with defect concentration in contrast to the predictions of the Elliott mechanism for spin relaxation in metals.
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    Electric conductivity and thermoelectric power of various polypyrroles
    (1987) Bender, Klaus; Gogu, Emil; Hennig, Ingolf; Schweitzer, Dieter; Münstedt, Helmut
    The dc-conductivity and thermoelectric power of electrochemically prepared polypyrroles have been investigated in the temperature range between 300 K and 1.3 K on unaged, aged (24-120 days at 80°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 of the polypyrroles investigated corresponds to that predicted by the variable range hopping model.
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    Frequency-dependent conductivity in pure and iodine-doped α-(BEDT-TTF)2I3
    (1987) Przybylski, Michael; Helberg, Hans W.; Schweitzer, Dieter; Keller, Heimo J.
    Measurements of the microwave conductivity at 10 GHz show a plateau below the metal-insulator transition at 135 K in contrast to the further dropping dc conductivity. In pure material the plateau is independent of frequency (4 GHz, 10 GHz. and 22 GHz), but in the temperature range above 135 K strong frequency dependence is observed. Iodine doping causes frequency dependence also in the plateau range. Particular doping rates give rise to several conductivity behaviors for different crystal directions. The results are discussed referring to CDW depinning and relaxation processes.
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    A stable superconducting state at 8K and ambient pressure in αt-(BEDT-TTF)2I3
    (1987) Schweitzer, Dieter; Bele, Petra; Brunner, Hermann; Gogu, Emil; Haeberlen, Ulrich; Hennig, Ingolf; Klutz, Thomas; Swietlik, Roman; Keller, Heimo J.
    We report bulk superconductivity at 8 K and ambient pressure in crystals of α t (BEDT-TTF)2I3. In contrast to the earlier observed metastable superconducting state at 8 K in crystals of β-(BEDT-TTF)2I3 here the superconducting state is stable and the crystals can be prepared by tempering α-(BEDT-TTF)2I3 above 70 °C for several days. ac-susceptibility measurements show that the observed superconducting state at 8 K is a bulk property of the crystals. Resistivity measurements indicate a sharp superconducting transition at 8 K with an onset temperature of about 9 K. The upper critical fields Hc2 at 1.3 K lie between 3 and 11 T depending on the direction of the magnetic field with respect to the crystal axes. ESR- as well as NMR-measurements indicate a total transformation of the α-phase crystals into the new superconducting α t -crystals after tempering.
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    Electronic band structure and point contact spectroscopy of the organic superconductor β-(BEDT-TTF)2I3
    (1987) Weger, Meir; Kübler, Jürgen; Schweitzer, Dieter
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