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201.
Reduced Clusters with Remarkable Topological and Electronic Properties of the Type of [V18O42(X)]n? (X = SO4, VO4) with Td-Symmetry and Related Clusters [V(18—p)As2pO42(X)]m? (X = SO3, SO4, H2O; p = 3, 4) The novel cluster-compounds Na6[V18O42H9(VO4)] · 21 H2O, (NH4)8[V18O42(SO4)] · 25 H2O, K6[V15As6O42(H2O)] · 8 H2O, (NH4)6[V14As8O42(SO3)], (NH4)6[V14As8O42(SO4)] and [N(CH3)3]4[4V14As8042(H20)] were prepared and characterized by IR- and UV/Vis/NIR-spectroscopy, magnetic measurements and complete crystal structure analysis. For structural data see Inhaltsübersicht. Topological relations to the rhombicuboctahedron spanned by 24 0-atoms of the genuine hypothetical a-Keggin ion, at which the square planes are capped by V?O or As2O groups, are discussed. Of particular interest are the ?extended”? Keggin ions [V18O42(X)]n- (X = SO4 VO4), (formaly derived from the hypothetical genuine a-Keggin ion by addition of six V?O groups) which have quite different electron populations in spite of the same structure of their cluster shells. 相似文献
202.
Hierarchical cluster analysis (HCA) and principal components analysis (PCA) were applied to find groups between similar depth-profiles in thin-layers investigated by Rutherford backscattering spectrometry (RBS).HCA yields in one run an objective hierarchy of similarity for several profiles. Among the similarity coefficients examined the linear measure, the Euclidean distance and the exponential measure respond with different sensitivity to overall shifts in direction of the concentration axis, whereas the correlation measure relates to parallelism of the profiles.For agglomerative HCA with Euclidean distance, a lowest significant linkage level has been defined by use of Fisher'sF-test. For divisive HCA based also on Euclidean distance, the maximum of a separating function marks the most separating cluster step. The outcomes of both proposals agree for the data set investigated.PCA is useful for verifying the results of HCA and yields additional information about the data structure. In the actual example quite different positions of features (concentrations at definite depths) in the space of the two first principal components hint at peculiarities during the metallurgical coating process. 相似文献
203.
以2013-2016年广州市各区(县级市)中考化学成绩的4种数据为指标,运用聚类分析研究广州市区域初三化学学业质量的发展状况。研究发现各区(县级市)主要分为3大类,部分区在不同年份的类别中移动,倾向于建立一个包括越来越多区域的第1大类。广州市区域初三化学学业质量逐步向优质均衡发展。系统的中学生化学探究活动和化学教师研训活动是实现这一发展的重要原因。 相似文献
204.
Qian-Feng Zhang Yu-Jie Liu Richard D. Adams Alexander Rothenberger Dieter Fenske Wa-Hung Leung 《Journal of Cluster Science》2006,17(3):445-455
Treatment of tetracopper(I)-phosphonitocavitand [1·Cu4(μ-Cl)4(μ4-Cl)] (2) (1 = tetraphosphonitocavitand [rccc-2,8,14,20-tetrakis-(iso-butyl)-phosphonitocavitand (C44H48O8P4Ph4)]) with PhSeSiMe3 in THF at low temperature afforded a novel polyanionic cluster [pyH]6[(CuCl)9(μ3-SePh)5(μ4-SePh)] (4) as a major product along with a new tetracopper(I)-phosphonitocavitand (3) with a centered μ3-Cl. Molecular structure of anionic cluster in 4 consists of six PhSe− bridging ligands containing five μ3-SePh and one exceptional μ4-SePh bridging nine copper atoms, of which eight copper atoms have trigonal coordination geometry and the other has distorted
tetrahedral geometry.
Dedicated to Professor Han-Qin Liu on the occasion of his 70th birthday. 相似文献
205.
206.
G. S. Zakharova L. Yu. Buldakova V. L. Volkov L. S. Molochnikov E. G. Kovaleva 《Russian Journal of Electrochemistry》2006,42(1):53-58
Complex vanadium and titanium oxides modified by copper ions are studied by the electrochemical and ESR methods. Oxides Cu x V2?y Ti y O5?δ·nH2O (0<y<1.33) have a layered structure and oxides Cu x Ti1?y V y O5+δ·nH2O (0<y<0.25), an anatase structure. The intercalation of cations Cu2+ into the hydrates leads to oxidation of V4+. According to ESR data, V4+ exists in the oxides in the form of VO2+ and an octahedral surround of oxygen (V4+?O6), respectively. The electroreduction of ions of d-elements and chemisorbed oxygen in the oxides is analyzed. The intercalation of cations Cu2+ alters the content of V4+ and the chemisorption ability of the oxides. Possible reasons for this phenomenon are discussed. 相似文献
207.
208.
The central V atom in bis[6-methyl-4-hydroxy-3-quinolinecarboxylate] mono(oxo)mono-hydroxy-vanadium(Ⅴ) (1), synthesized by the hydrothermal treatment of ethyl 6-methyl-4-hydroxy-3-quinolinecarboxylate and V2O5, has a distorted octahedral coordination geometry formed by six oxygen atoms from two oxygen atom of two hydroxy groups and two oxygen atoms of two carboxylate groups as well as one oxo group and hydroxy group. CCDC: 285592. 相似文献
209.
We have performed calculations on the fullerene cage and stacked structures of neutral and ionic Si50 cluster by full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method. It is found that the neutral and charged fullerene cages relax into distorted structures resembling puckered balls. Their electronic structures are remarkably similar besides their geometrical structures. However, the relaxed cages are still not so stable as the stacked structure built from tricapped trigonal prism. By comparison, for the fullerene cages and stacked structures of neutral and ionic Si60 cluster, similar characteristics are found. 相似文献
210.
The gas-chromatographic method is used to study the interaction of water and methanol molecules with active hydrophilic centres
existing at the surface of thermally exfoliated graphite and graphitized thermal carbon black. The concentration of carboxyl
and phenol hydroxyl groups at the surface of these sorbents is determined, and heats of adsorption of the studied molecules
are shown to be
and 28−25 kJ/mol, respectively. It is also shown that adsorption of water at the hydrophilic centres at lowest relative pressure
values takes place with formation of clusters consisting of n = 2 water molecules. 相似文献