Browsing by Author "Neugebauer, Franz A."

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    Spectroscopic investigations of the lowest triplet state of s-tetrazines
    (1992) Gückel, Friedemann; Maki, August H.; Neugebauer, Franz A.; Schweitzer, Dieter; Vogler, Helmut
    We report on the electronic and triplet state ODMR spectroscopy of s-tetrazine, 3,6-dimethyl-, 3,6-dimethoxy- and 3,6-bis(methylthio)-s-tetrazines. Zero field splitting parameters were obtained by ODMR monitoring both the delayed fluorescence and the phosphorescence in neat single crystals. The S1 and T1 exciton electronic origins are reported. The zero field splitting tensor is nearly axially symmetric with |D| approximately 0.4 cm-1. This value is found to be in good agreement with calculations based on magnetic dipole-dipole coupling in a 3B3u (nπ*) state. The calculations predict a positive value for D with the major axis passing through the C atoms at the 3 and 6 positions.
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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.