Universität Stuttgart
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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 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 Electrons and holes in InSb under crossed magnetic and stress fields. 1, Theory(1988) Trebin, Hans-Rainer; Wolfstädter, Bernd; Pascher, Harald; Häfele, Hans-GeorgIn a series of four papers magnetooptical transitions are presented for InSb crystals, which are subjected to uniaxial stress perpendicular to the magnetic field. Here, in the first paper, we establish an 8×8 k⋅p Hamiltonian matrix for stress Tǁ[100] and field Bǁ[001] and diagonalize it exactly. The dependence of valence and conduction states on stress and longitudinal momentum is discussed and compared with the geometry of parallel fields TǁBǁ[001]. Characteristic features are extracted for inter- and intraband transitions. Under crossed fields, the levels are separated much stronger with stress, yielding more insight than in the parallel configuration.Item Open Access Self-consistent modelling of pulsar magnetospheres(1989) Herold, Heinz; Ertl, Thomas; Finkbeiner, Bernd; Ruder, HannsThe magnetosphere of a rapidly rotating, strongly magnetized neutron star with aligned magnetic and rotational axes (parallel rotator) is modelled numerically. Including the radiation of the particles accelerated to relativistic energies as an efficient damping mechanism, we obtain a quasi-stationary selfconsistent solution to this classical problem. The numerical simulation, which was started from the well-known vacuum solution, yields a global magnetospheric structure that can be characterized by two regions of oppositely charged particles, which eventually produce a relativistic pulsar wind, separated by a vacuum gap of considerable extent.Item Open Access Particle motion in pulsar magnetospheres(1987) Finkbeiner, Bernd; Ertl, Thomas; Herold, Heinz; Ruder, HannsThis report discusses some new results we found in studying the trajectories of single charged particles in the vacuum magnetosphere of a pulsar using the oblique rotator model. We believe that investigations of individual particles in the vicinity of the star can be useful for a better understanding of some fundamental problems of pulsar physics, e.g. the global structure of the magnetosphere or the pulsar radiation.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 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 Quasicrystal structures from the crystallographic viewpoint(1988) Gähler, Franz; Fröhlich, J. (Prof. Dr.)Quasikristalle sind neuartige Phasen, die in schnell abgekühlten Metall-Legierungen vorkommen. Ihre wichtigste Eigenschaft ist, dass Ihre Fourier-Transformierte aus scharfen Bragg-Peaks besteht, deren Positionen und Intensitäten eine Punktsymmetrie haben, die mit einer dreidimensionalen periodischen Struktur nicht verträglich ist. Die Positionen der Bragg-Peaks eines Quasikristalls können jedoch alle als ganzzahlige Linearkombinationen von endlich vielen fundamentalen Wellenvektoren geschrieben werden; dies legt nahe, diese Strukturen als Schnitt durch eine höherdimensionale, periodische Struktur aufzufassen.Item Open Access Wärmeübertragung in einem axial rotierenden, durchströmten Rohr im Bereich des thermischen Einlaufs. T. 2, Einfluß der Rotation auf eine laminare Strömung(1989) Weigand, Bernhard; Beer, HansDer Einfluß der Rotation auf das Temperaturprofil und die Wärmeübergangszahl einer laminaren Rohrströmung im Bereich des thermischen Einlaufs wird theoretisch untersucht. Es wird angenommen, daß das Geschwindigkeitsprofil voll ausgebildet ist. Die Rotation hat einen destabilisierenden Einfluß auf die Laminarströmung, die umschlägt und turbulent wird. Aufgrund der Anfachung der Turbulenz durch die Rotation verbessert sich die Wärmeübertragung mit steigender Rotations-Reynoldszahl und die thermische Einlauflänge nimmt beträchtlich ab.