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991.
Six new complexes: [Ln2(pzda)3(H2O)2] · 2.5H2O (Ln = Nd, (1); Eu, (2)), [Co(pzda) (bpe)] · 0.125(bpe) · 1.75H2O (3), [Mn(pzda)(H2O)1.5] (4), [Co2(pzda)2(bpe)(H2O)4] · 0.5(CH3OH) · H2O (5) and [Co(pzda)(2,2′-bpy)(H2O)] · 0.5H2O (6) (H2pzda = pyrazine-2,6-dicarboxylic acid, bpe = 1,2-bis(4-pyridyl)ethane, 2,2′-bpy = 2,2′-bipyridine) were obtained from metal salts and H2pzda under hydro(solvo)thermal conditions. The single crystal X-ray structural analysis reveals that the title complexes have different structures, ranging from zero- to three- dimensions, which are mainly due to the different metal ions, and especially the coordination modes of the pzda ligands. Complexes 1 and 2 have 3D metal-organic frameworks containing a 1D tri-strand array, in which the pzda ligand adopts a pentadentate mode to link lanthanide ions. Complex 3 has a 2D metal-organic framework, in which the pzda ligand acts in a tetradentate mode to connect Co(II) ions into 1D chains, which are further connected by bpe spacers into a 2D framework. While in 4, both of the two carboxylate groups of the pzda ligand adopt μ2-O bridging modes to link Mn(II) ions into a 1D coordination polymer, which is further assembled into a 2D supramolecular network containing double-stranded hydrogen-bonded helical chains. In both 5 and 6, the pzda ligand binds metal ions as a tridentate ligand (ONO mode) to form zero dimensional structures. Complex 5 is a binuclear molecule, while 6 is a mononuclear complex, which can be attributed to the bridging ligand bpe for 5 and the terminal auxiliary ligand 2,2′-bpy for 6. 相似文献
992.
A. Maignan V. Caignaert V. Pralong D. Pelloquin S. Hébert 《Journal of solid state chemistry》2008,181(5):1220-1226
The “114” YBaCo4O7 cobaltite undergoes structural transition just beyond room temperature at TS∼310 K. Correspondingly, its signature in the physical properties is detected by T-dependent measurements of electrical resistivity, magnetic susceptibility and thermoelectric power. It is found that low-level substitutions of divalent (M=Zn2+) or trivalent (M=Ga3+, Al3+) cations for cobalt according to the YBaCo4−xMxO7 formula with x?0.4 have a strong impact upon this transition. On the one hand, Zn2+ substitutions preserve the transition but with TS decreasing as x increases. On the other hand, for x=0.2 Ga3+ or Al3+, the transition is suppressed, i.e., for only 5% trivalent foreign cation substituted for cobalt. Though at first, this contrasted behaviour between divalent and trivalent substituting cations appears to be linked to the opposite evolution of hole carriers “Co3+” concentration with x, a possible destabilization of 3Co2+: 1Co3+ charge ordering induced by the M3+ cations is considered. 相似文献
993.
从自然地理条件、地质条件、环境质量、环境地质问题等方面着手,以地形地貌、区域地壳稳定性、岩(土)体工程地质特征、环境污染、地质灾害为要素开展了自贡市城市地质环境质量评价;采用了权重法、层次分析法等计算方法得出了地质环境综合评价指数,对自贡市进行了地质环境评价分区;为城市的发展规划提供了可靠的地质依据。 相似文献
994.
为了解幼儿园中班小儿生长发育状况以指导小儿营养状况评价,对幼儿园中班(5.6±0.6)岁小儿的身高、坐高、体质量、胸围、头围和上臂围等指标进行了测量,并与国内常模组小儿的生长发育指标进行了比较。结果表明,幼儿园中班男童的体质量大于国内常模组男童的体质量,两组比较有显著性差异(P<0.05);女童的胸围小于国内常模组女童胸围,两组比较有显著性差异(P<0.05);其它生长发育指标与国内常模组小儿比较无显著性差异。提示该幼儿园中班男童有营养过足的问题,女童的胸围较国内常模组女童胸围小,故呈“豆芽型”。 相似文献
995.
Leroy V Devaud M Hocquet T Bacri JC 《The European physical journal. E, Soft matter》2005,17(2):189-198
The dynamics of a two-dimensional N-bubble static cloud is investigated and shown to be well described by an N-degree of freedom harmonic oscillator model, at least at low enough frequencies. Eigenmodes and eigenfrequencies are calculated and compared with experimental results obtained with an assembly of bubbles caught up under a net in a water tank. Accordance is found to be excellent in the frequency range of validity of the model, the limits of which are discussed. An interpretation of the low-frequency branch of Foldy’s dispersion relation in bubbly liquids is suggested in terms of “bubble waves” in a quasi-incompressible medium. 相似文献
996.
N. V. Banichuk 《Journal of Optimization Theory and Applications》1976,20(1):111-127
The problem of determining the shape of an elastic body which is optimal for a whole class of loads is formulated. Its general solution scheme, based on a minimax approach, is indicated. The optimization problem of an elastic beam is studied for both the simply supported case and the cantilevered case, and some specific properties of the optimal shape are determined.The author is grateful to Professor A. I. Lurie, Professor F. L. Chernousko, and Professor G. S. Shapiro for useful discussions of the results. 相似文献
997.
998.
999.
在有机化学合成实验中影响实验结果和产率的因素有很多。通过让学生自主研究1-溴丁烷的制备过程中实验条件、实验装置和实验步骤等合成条件对实验结果的影响,以及对实验总体的分析,从而让学生充分理解和掌握了进行有机合成实验的操作技能和思维方法,以及创新能力,为以后有机化学实验的学习提供了良好的基础。同时,也探讨了一些关于有机化学实验的有效教学方法,为以后有机化学实验教学研究奠定了一定基础。 相似文献
1000.
A rare porous metal-phosphonocarboxylate framework with ultrahigh thermal stability over 500℃ was obtained, which can be transformed into three different cluster-based frameworks with the same CaF2-type topology. 相似文献