Universität Stuttgart
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Item Open Access Metallic coordination polymers using CS2 as starting material(1987) Keller, Heimo J.; Klutz, Thomas; Münstedt, Helmut; Renner, Gerd; Schweitzer, DieterOrganic 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.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 Nuclear magnetic shielding tensors for 1H, 13C, and 15N in organic solids(1975) Spiess, Hans Wolfgang; Haeberlen, Ulrich; Kempf, Jürgen; Schweitzer, DieterA survey will be given of nuclear magnetic shielding tensors obtained by multiple pulse techniques for 1H in carboxylic acids and by high field NMR for 13C in carbonyl- and carboxyl groups of aromatic compounds and for 15N in pyridine and nitrobenzene.Item Open Access Spectroscopic properties of kekulene(1981) Schweitzer, Dieter; Hausser, Karl H.; Diederich, Francois; Staab, Heinz A.; Vogler, HelmutKekulene [1,2] is the first example of a new class of aromatic compounds in which the annelation of six membered rings leads to a cyclic system enclosing a cavity with hydrogen atoms.Item Open Access Organic metals from chiral BEDT-TTF donors(1991) Chen, Ben-ming; Deilacher, Frank; Hoch, Matthias; Keller, Heimo J.; Wu, Pei-ji; Gärtner, Stephan; Kahlich, Siegfried; Schweitzer, DieterWe have shown that is is possible to obtain organic metals from chiral molecules. The X-ray results prove an oxidation number of + 1.5 for the radical cations in at least two cases. To our best knowledge. these are: the first examples of BEDT-TTF-related radical cation salts with this oxidation number. As expected, we obtained statistically disordered crystals, containing the two different enantiomers in a "racemic" mixture. The broad smeared-out phase transitions are probably due to this disorder, or may be caused by the three-dimensional interactions which have been observed, so far, only once in a BEDT-TTF radical salt. We will crystallize the metallic compounds using "optically pure" isomers, in the hope to be able to isolate chiral metals.Item Open Access BEDT-TTF radical salts: organic metals and superconductors(1987) Schweitzer, DieterA review of the structural, electronic and superconducting properties of some BEDT-TTF-radical salts is given.Item Open Access Proton relaxation in the superconducting organic solid (BEDT-TTF)2Cu(NCS)2: evidence for relaxation by localized paramagnetic centers(1990) Klutz, Thomas; Haeberlen, Ulrich; Schweitzer, DieterThe nonexponential character of the build-up of the nuclear magnetization usually increases on lowering the temperature. Superconducting fluctuations have been offered in a speculative way as an explanation for the nonexponential spin relaxation. We have observed the same relaxation behaviour in our investigation of the proton spin relaxation in (BEDT-TTF)2Cu(NCS)2 which is an organic conductor at room temperature and becomes a superconductor at Tc=10.4 K at ambient pressure. As we noticed during preliminary measurements that the degree of deviation from exponential relaxation depends on the sample under study we decided to do experiments under controlled conditions of sample preparation.Item Open Access Electronic interactions between polycyclic arenes in cyclophanes(1988) Haenel, Matthias; Schweitzer, DieterThe π-π interaction between polycyclic arenes and the effects of orientation were studied in [2.2]-, [3.3]-, and [3.2]naphthalenophanes, [2]naphthaleno[2]paracyclophanes, and syn- and anti[2.2](2,7)fluorenophane by electron absorption and emission spectroscopy as well as by optically detected magnetic resonance (ODMR) of the excited triplet state. The π-π interaction in the excited singlet and triplet state was found to be highest if a maximal number of sixmembered rings of the interacting arenes in a parallel orientation are completely eclipsed. Similarly, the π-π interaction between the nonbonding nitrogen electron pair and the aromatic π electrons was investigated in isomeric etheno-bridged naphthalenopyridinophanes and an anthracenopyridinophane; in these pyridinophanes, the pyridine rings are fixed perpendicularly above different sites of the naphthalene and anthracene units, respectively.Item Open Access 15N and 13C spin lattice relaxation in neat liquids at high magnetic fields(1975) Schweitzer, Dieter; Spiess, Hans WolfgangGeneral features of 15N spin lattice relaxation in nitrobenzene, pyridine and triethanolamine are discussed and compared with l3C relaxation mechanisms.Item Open Access Band structure calculation and tunneling measurements in (BEDT-TTF)2X (X=I3, IAuI)(1990) Weger, Meir; Nowack, Andreas; Schweitzer, Dieter; Kübler, Jürgen; Bentum, Jan M. van; Sommers, Charles S.At about the same time when little proposed room-temperature superconductivity in organic polymers, it was suggested that the high-Tc of the more conventional A-15's is associated with their one-dimensional electronic band structure. When TTF-TCNQ was discovered in 1973, it was suggested that the electron-phonon coupling in this 1-D organic molecular crystal is responsible for the metal-to-insulator (Peierls) transition at 52 K2, and reducing λ will cause a crossover to a superconducting state. Since then, the electronic structure, the conduction mechanism, and the superconducting mechanism were subject to controversy. Therefore, it is of some importance to establish whether the electronic band structure, and conduction mechanism, are similar to those in more conventional metals, and whether the superconductivity mechanism is the normal BCS phonon-mediated interaction.