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Hans Bock Klaus Ruppert Eberhardt Herdtweck Wolfgang A. Herrmann 《Helvetica chimica acta》1992,75(6):1816-1824
Structural Changes on Reduction of 9-(Diphenylmethylidene)fluorene by Sodium Metal to Sheets of (R2O)Na⊕- Connected Hydrocarbon Dianions The single-crystal structure of 9-(diphenylmethylidene)fluorene (monoclinic, space group P21/n, Z = 4) proves a C?C bond length of 135 pm and a twisting of the two Ph rings out of the methylidene-fluorene plane by 70° and 83°. Its reduction in Et2O solution by a Na mirror under Ar yields dark green crystals with a metallic luster. Their structure, determined in a N2 flow cooled to 223 K (monoclinic, space group C2/c, Z = 4), reveals sheets of hydrocarbon dianions, connected by sodium(diethylether) links. The Na centers are sixfold coordinated as half-sandwiches to the fluorene benzo rings and threefold allylic to the Ph rings. In the dianion of 9-(diphenyl-methylidene)fluorene, the central C?C bond is stretched by 13 pm to 148 pm length, and the two molecular cyanine-like halves are twisted by 51° relative to each other. Both the contact-ion multiple structures as well as the structural changes on twofold reduction are discussed by way of comparison with literature examples and based on semiempirical calculations. 相似文献
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The g-factors of the first-excited Jπ = 2+ states of 24Mg and 26Mg have been measured with the ion-implantation perturbed angular correlation technique (IMPAC). The precession of the spins of nuclei recoiling into a magnetized iron backing is predominantly caused by the transient magnetic field for these very light and short-lived (τm ≈ 1 ps) nuclei. The transient field, which attains a value of 200 T for the Mg isotopes, is present only during the slowing-down of the recoiling nucleus and results in average precession angles of about 1.5 mrad. The experimental results are treated in the framework of the transient field theory of Lindhard and Winther. This yields g-factors of g = +0.42b ± 0.09 and g = +1.3 ± 0.3 for 24Mg and 26Mg, respectively. The results are compared with theoretical predictions and for 24Mg also with a recent time-differential deorientation experiment. 相似文献
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We observe a drastic broadening of the photoemission lines of the 2p core levels of Al when the surface sensitivity of the measurement is enhanced by an appropriate choice of the photon energy using synchrotron radiation. This surface broadening appears to be quite universal and also occurs for other substances like, e.g. Au. Its possible origin is discussed. There is no surface induced shift of the Al 2p binding energy within ± 40 meV. 相似文献
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We probe final energy bands of Cu in the kinetic energy range 20 eV ? E ?120 eV by angle resolved photoemission techniques. We observe deviations from free electron like behaviour in agreement with a LEED-type KKR calculation (Jepsen [5]). The lifetime broadening of the final bands at 60 eV kinetic energy is ~5 eV (FWHM). 相似文献