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31.
Magnetically disordered, strong correlated itinerant electron systems are studied within the Hubbard model. Following an alloy analogy, the approximated system hamiltonian contains local vectoral magnetic fields at the atomic sites, which can be oriented into all space directions. The statistical system of the localized magnetic moments (due to the fields) is treated by the aid of a generalized CPA-technique. Supposing a macroscopic magnetic structure of sublattice antiferromagnetism, the formation of incomplete antiferromagnetic ordering of the localized moments is examined. The results show, that the electron density plays an essential roll for the question, whether or not it is possible to go beyond the pure (itinerant) antiferromagnetic state. Including the results of earlier papers for homogeneous macroscopic magnetic structure, on the whole scale of electron densities it is summed up (at zero temperature), where the different states (without-, with incomplete- or with complete magnetic order) are able to exist. It is shown, for fixed density respectively, which different phases are passed through on changing the coupling constant.Work supported by the Deutsche Forschungsgemeinschaft 相似文献
32.
Eliseu O. De Oliveira Carlos A. Brandt Richard A. Glennon 《Tetrahedron letters》2007,48(36):6393-6396
Novel 2-, and N-substituted 5-methylene-pyrrolidine benzamides and 2-, 3-, and N-substituted 5-methylene-2-pyrroline benzamides were synthesized for the first time in a straightforward manner and in good yields via iodocyclization of γ- and α-alkenyl-β-enaminoesters, respectively. The key step in the process is the synthesis of the methylene-pyrrolidine iodide and methylene-2-pyrroline iodide intermediates. Functional group inter-conversion of these iodides to their amino analogs, and their subsequent coupling to benzoic acids via EDC, afforded the above pyrrolidine/2-pyrroline-substituted benzamides in yields of around 75%. 相似文献
33.
Dieter Naumann Prof. Dr. Wieland Tyrra Dr. Hendrik T. M. Fischer Silke Kremer 《无机化学与普通化学杂志》2007,633(4):527-528
Tetrakis(pentafluorophenyl)tellurium(IV), Te(C6F5)4, was prepared from the reaction of TeCl4 and Mg(C6F5)Br. Crystallization of the crude product from n‐pentane at ?25 °C gave suitable single crystals. The title compound crystallizes in the monoclinic space group P21/c (Z = 8) with two independent molecules per unit cell. 相似文献
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M. I. Krivopustov J. Adam V. Bradnova R. Brandt V. S. Butsev P. I. Golubev V. G. Kalinnikov J. Karachuk B. A. Kulakov E.-J. Langrock G. Modolo M. Ochs R. Odoj A. N. Premyshev V. S. Pronskich Th. Schmidt V. I. Stegailov J. S. Wan V. M. Zupko-Sitnikov 《Journal of Radioanalytical and Nuclear Chemistry》1997,222(1-2):267-270
First experiments on the transmutation of long-lived129I and237Np using relativistic protons of 3.7 GeV are described. Relativistic protons generate in extended Pb-targets substancial neutron fluences. These neutrons get moderated in paraffin and are used for transmutation as follows:129I(n,)130I and237Np(n,)238Np. The isotopes130I (T
1/2-12.36 h) and238Np (T
1/2=2.117 d) were identified radiochemically. One can estimate the transmutation cross-section (n,) in the given neutron field as (129I(n,))=(10±2)b and (237Np(n,))=(140±30)b The experiments were carried out in November 1996 at the Synchrophasotron, LHE, Dubna, Russia. The investigation has been performed at the Laboratory of High Energies, JINR, Dubna. 相似文献
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Ingeborg Csöregh Thomas Brehmer Silke I. Nitsche Wilhelm Seichter Edwin Weber 《Journal of inclusion phenomena and macrocyclic chemistry》2003,47(3-4):113-121
X-ray crystal structures are reported of a free host compound 1, comprising two diphenylmethanol terminal groups attached to a central 9,10-ethynyl substituted anthracene unit, and of three inclusion compounds of a fluoren-9-ol substituted analogous host 2 with acetone, dimethyl sulphoxide (DMSO) and dimethylformamide (DMF) as guest, respectively. Despite the presence of two hydroxyl groups in 1, there is no O–H...O hydrogen bond between the molecules in the guest free crystal – only weaker C–H...O interactions and van der Waals' type connections. In the inclusion compounds of 2, H-bonded 1:2 host–guest associates are formed, where each of the host hydroxyl groups binds to a guest oxygen atom. The orientations of the host–guest connections in these complexes vary, being E for acetone and Z for both DMSO and DMF guests, relative to the host anthracene unit. The DMSO and DMF inclusion compounds of 2 proved to be isostructural. 相似文献