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 Temperature and angular dependence of the upper critical field in β-(BEDT-TTF)2I3 and its deuterated analogue(1986) Heidmann, Claus Peter; Andres, Klaus; Schweitzer, DieterWe present measurements of the temperature and angular dependence of the upper critical fields of β-ET2I3 and d-β-ET2I3. The data are analyzed in terms of an anisotropic effective mass model. The results of cooling rate experiments are reported and the effect of deuteration on superconductivity is discussed.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 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.Item Open Access Excited electronic states of flavin-containing coenzyme models(1988) Gückel, Friedemann; Schweitzer, Dieter; Becker, Katja; Schirmer, Rolf Heiner; Zipplies, Matthias F.; Staab, Heinz A.In order to gain further insight into the physical basis of flavin-catalyzed reactions, the interactions of a flavin with a second flavin and with other aromatic ring systems were studied. For this purpose compounds through 1 were synthesized These compounds contain the interacting units in defined geometric orientation. A monomeric flavin and glutathione reductase a flavoenzyme of known active-site chemistry, were included as reference molecules. The present report deals with excited triplet states of the flavin compounds as studied by optical spectroscopy and optically detected magnetic resonances (ODMR) at 1.3K.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 Kinetics of the triplet state of 2,3-dichloroquinoxaline from microwave-induced phosphorescence transients(1973) Schweitzer, Dieter; Zuclich, Joseph A.; Maki, August H.The phosphorescent state of 2,3-dichloroquinoxaline doped into single crystals of durene and 1,2,4,5-tetrachlorobenzene has been studied using several methods based upon optical detection of magnetic resonance (ODMR). Flash excitation and continuous optical pumping methods are described and analysed. Phosphorescent transient effects caused by spin-lattice relaxation and variable intersystem crossing rates are observed and described using first-order solutions of the appropriate rate equations. The effects of spatial polarization of the phosphorescence (anisotropic spatial distribution of phosphorescence intensity) of single crystals on ODMR signals is observed and discussed. The spatial polarization of emission can cause difficulties in determining relative radiative rate constants of the triplet sublevels in oriented samples, but can yield information about the linear polarization of the emission analogous to that obtained by conventional means using polarizers.Item Open Access Electronic spectra and triplet state properties of superphane(1986) Schweitzer, Dieter; Hausser, Karl H.; Vogler, Helmut; Staab, Heinz A.; Boekelheide, VirgilThe emission and the zero-field splitting parameters D and E of the superphane 1 and the [25](1,2,3,4,5)-cyclophane 2 are investigated. The large number of six and five methylene bridges, respectively, leads to a more rigid molecular frame and to a smaller transanular distance as compared to other [2.2]cyclophanes. The experimental results exhibit characteristics features which are due to these unusual properties; they are discussed and compared with semi-empirical Π-electron calculations.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.