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991.
992.
Elisabeth Bouwman J. Christine Ten Hove Willem L. Driessen Jan Reedijk 《Polyhedron》1988,7(24):2591-2595
Transition metal coordination compounds with the novel N2S2-donor ligand 1,6-bis(4(5)-imidazolyl)-2,5-dithiahexane (abbreviated bhdhx) with general formulae M(bhdhx)(NO3)2(M = Co, Ni, Cu) and M(bhdhx)(H2O)2(BF4)2 (M = Cu, Zn) have been isolated. In all compounds the ligand is tetradentate with both thioether sulphurs and imidazole nitrogens coordinating. In all compounds the metal ions are six-coordinated in a distorted octahedral geometry with either nitrates or water molecules as the fifth and sixth ligands. This is confirmed by the ligand field spectra, which agree with a distorted octahedral coordination. The distortion from octahedral, indicated by the ligand field spectrum of the cobalt nitrate compound is such that the S atoms of the ligands must be at a very large distance from the metal ion. A single crystal of Cu(bhdhx)(NO3)2 was used in a structure determination: orthorhombic space group Pbcn, a = 14.351(5), b = 8.554(3), c = 13.057(4) Å, Z = 4, and T = 293 K. The structure was solved by heavy atom techniques and refined by least-squares methods to a residual R value of 0.033 for 847 significant reflections. The copper ion is at a special position on a two-fold axis, which causes a two-fold symmetry in the ligand. The coordination geometry of the copper atom is distorted octahedral with the two nitrates and the two thioether sulphurs in a cis position, and the imidazole nitrogens trans. The copper to nitrogen distances are 1.933(4) Å, the copper to sulphur distances are 2.495(1) Å, and the copper to oxygen distances are 2.280(3) Å. 相似文献
993.
Christine Videlot-Ackermann Takashi Isoshima Abderrahim Yassar Hiroyuki Sasabe 《Applied Surface Science》2006,253(3):1517-1521
Electroabsorption (EA) studies at room temperature on organic thin films based on a dicyanovinyl-quaterthiophene 4T-V(CN)2 are reported. An electric field modulation is applied to the samples for two different electrode geometries, i.e. sandwich and coplanar versus the organic layer. Changes in optical absorption coefficient of 4T-V(CN)2 based thin films are measured and analyzed to determine the character of the optical transition in the visible range (400-800 nm). Depending on the experimental electrode configuration, magnitude of electroabsorption responses are different, possibly due to different distribution of the externally applied electric field. The results indicate a higher resolution of EA response for the sandwich electrode configuration and confirm the charge transfer exciton character of 4T-V(CN)2 in contrast to the unsubstituted quaterthiophene 4T. Finally, a third-order nonlinear susceptibility χ(3) (−ω; ω, 0, 0) of 16 × 10−12 e.s.u. is obtained. 相似文献
994.
995.
U. Schulz S. Jakobs B. Anton N. Kaiser 《Fresenius' Journal of Analytical Chemistry》1995,353(5-8):740-742
Lenses for eye glasses of thermosetting material CR39 and optical lenses of polycarbonate have been investigated with respect to their moisture absorption behavior. The moisture content of polymer lenses has been determined by analyzing transmission spectra in the near infrared (NIR). The surface topography was characterized by Atomic Force Microscopy (AFM). In spite of the fact that CR39 takes up essentially more water, the formation of surface defects is not remarkable compared with lenses of polycarbonate. 相似文献
996.
Abstract— Sporulation of starving plasmodia of Physarum polycephalum was found to be induced by far-red light, blue light or heat shock, each of which is perceived by a different input receptor system. The branched signal transduction pathway was mapped and the time-dependent formation of some of its components analyzed. 相似文献
997.
Ohne Zusammenfassung
Herrn Professor Dr. Dr.h.c.mult. Otto Haupt mit den besten Wünschen zum 100. Geburtstag gewidmet 相似文献
998.
Cognitive level in problem segments and theory segments 总被引:1,自引:0,他引:1
Barbara Drollinger-Vetter Frank Lipowsky Christine Pauli Kurt Reusser Eckhard Klieme 《ZDM》2006,38(5):399-412
Problems play an important role in mathematics instruction and are therefore frequently seen as central points of application for measures of instructional development. The research project “Quality of instruction and mathematical understanding in different cultures” examines the cognitive level of practice problems and theory problems in a three-lesson unit on the Introduction to Pythagorean theorem1: Analogously to the TIMSS 1999 video study, a differentiation was made between the cognitive level of problem statement and the cognitive level of problem implementation. Additionally, the lesson time was also divided into practice and theory segments. The results show that teachers with a high proportion of connection activities in practice segments do not necessarily also spend a greater proportion of time on an analogous level for theory. 相似文献
999.
1000.