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排序方式: 共有136条查询结果,搜索用时 15 毫秒
41.
Christian R. Samanamu Monika L. Amadoruge Charles S. Weinert James A. Golen Arnold L. Rheingold 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6):1389-1395
Abstract We have employed the hydrogermolysis reaction for the preparation of rare branched oligogermanes, and have obtained for the first time the X-ray crystal structures of several branched tetragermanes, including (Ph3Ge)3GePh, (Ph3Ge)3GeH, and (Ph3Ge)3GeX (X = Cl or Br). We also have at our disposal branched tetragermanes having the formula (EtOCH2CH2Bu n 2Ge)3GePh, where the ethoxyethyl substituent serves as a protecting group for a germanium–hydride active site. These reagents have been employed for the stepwise synthesis of higher branched systems having up to 13 bonded germanium atoms in the oligomer backbone. The synthesis, structures, and physical characteristics of these systems are described. GRAPHICAL ABSTRACT 相似文献
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43.
Co(II), Ni(II), Mn(II), Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, Ti(IV), V(IV), Zr, Hf, Th, Al, Sc, Y, La, the lanthanides and also U(VI), which accompany copper(II) in hydrochloric acid-acetone mixtures, can be separated from copper by eluting copper(II) with 0.50 M hydrobromic acid in 85% acetone from a column of AG 50W-X8 resin, 200–400 mesh, while all these elements are retained by the column quantitatively. Separations are sharp and quantitative, as is demonstrated by results for some synthetic mixtures. Some relevant elution curves are presented. 相似文献
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Magnetism and hyperfine fields at transition metal surfaces are discussed using state-of-the-art local spin density methods.
Emphasis is placed on recent results obtained for the Fe(001), Ni(001), Cr(001) and Ag/Fe(001) ferromagnetic surfaces, and
for the Knight shift in Pt(001). 相似文献
46.
Wetherby AE Goeller LR DiPasquale AG Rheingold AL Weinert CS 《Inorganic chemistry》2007,46(18):7579-7586
The protonolysis reaction of the germanium(II) amide Ge[N(SiMe3)2]2 with calix[4]arene and calix[8]arene furnishes the two germanium(II) calixarene complexes {calix[4]}Ge2 and {calix[8]}Ge4, respectively, which have been crystallographically characterized. The calix[4]arene complex contains a Ge2O2 rhombus at the center of the molecule and is one of the only four germanium(II) calix[4]arenes that have been structurally characterized. The calix[8]arene species is the first reported germanium calix[8]arene complex, and it exhibits an overall bowl-shaped structure which contains two Ge2O2 fragments. The latter complex reacts with Fe2(CO)9 to yield an octairon compound, which has also been structurally characterized and contains four GeFe2 triangles arranged around the macrocyclic ring. The germanium(II) centers are oxidized to germanium(IV) in this process, with concomitant reduction of the neutral diiron species to Fe2(CO)(8)2- anions. 相似文献
47.
Ionic‐Radius‐Driven Selection of the Main‐Group‐Metal Cage for Intermetalloid Clusters [Ln@PbxBi14−x]q− and [Ln@PbyBi13−y]q− (x/q=7/4, 6/3; y/q=4/4, 3/3)
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Dr. Rodica Ababei Prof. Dr. Werner Massa Bastian Weinert Patrik Pollak Dr. Xiulan Xie Dr. Rodolphe Clérac Dr. Florian Weigend Prof. Dr. Stefanie Dehnen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):386-394
Reactions of the binary, pseudo‐homoatomic Zintl anion (Pb2Bi2)2? with Ln(C5Me4H)3 (Ln=La, Ce, Nd, Gd, Sm, Tb) in the presence of [2.2.2]crypt in ethane‐1,2‐diamine/toluene yielded ten [K([2.2.2]crypt)]+ salts of lanthanide‐doped semimetal clusters with 13 or 14 surface atoms. Single‐crystal X‐ray diffraction and energy‐dispersive X‐ray spectroscopy indicated the presence of the anions [Ln@Pb6Bi8]3?, [Ln@Pb3Bi10]3?, [Ln@Pb7Bi7]4?, or [Ln@Pb4Bi9]4? in single or double salts; the latter showed various ratios of the components in the solid state. The anions are the first ternary intermetalloid clusters comprising only elements of the sixth period of the periodic table, namely, Pb, Bi and lanthanides. This study, which was complemented by ESI mass spectrometry and 139La NMR spectroscopy in solution, rationalizes a continuous development of the ratio of 13:14‐atom cages with the ionic radius of the embedded Ln3+ ion, which seems to select the most suitable cage type. Quantum chemical investigations helped to analyze this situation in more detail and to explain the observed subtle influence of the atomic radii. Magnetic measurements confirmed that the embedded Ln3+ ions keep their expected paramagnetic or diamagnetic nature. 相似文献
48.
Christian R. Samanamu Nicholas F. Materer Charles S. Weinert 《Journal of organometallic chemistry》2012
The germanium-based neo-pentane analogue (Me3Ge)4Ge has been characterized by UV/visible spectroscopy, cyclic voltammetry, and 73Ge NMR spectroscopy as well as by density functional theory (DFT) calculations. The absorption maximum for (Me3Ge)4Ge is blue-shifted relative to those for other related branched oligogermanes (Ph3Ge)3GeH and (Ph3Ge)3GePh, and this species is also the most difficult to oxidize among these three compounds. DFT calculations indicate the HOMO of (Me3Ge)4Ge is stabilized relative to those for both tetragermanes by ca. 0.5 eV and therefore the theoretical and experimental results are in agreement. The 73Ge NMR spectrum of (Me3Ge)4Ge exhibits two resonances and the feature corresponding to the central formally zero-valent germanium atom is shifted far upfield and was observed at δ ?339 ppm. 相似文献
49.
I. G. Hill C. M. Weinert L. Kreplak B. P. van Zyl 《Applied Physics A: Materials Science & Processing》2009,95(1):81-87
Self-assembled monolayers are widely used to modify the gate dielectric/semiconductor interface in organic thin-film transistors.
By modifying the interaction between the molecular semiconductor and the substrate, thin-film ordering and the electronic
properties of the semiconducting channel can be controlled. The modified semiconductor/dielectric properties result in macroscopically
observed changes in the charge-carrier mobilities, threshold voltages, subthreshold swing and transfer characteristic hysteresis.
The latter two are determined by the density of charge-trapping states at the interface. Here, we investigate the influence
of the thickness of the self-assembled monolayer, via the alkyl chain length in n-alkyl phosphonic acid-based monolayers on
SiO2, on the electronic properties of pentacene-based organic thin-film transistors. Rather than a monotonic increase or decrease
in performance with increasing chain length, we have found that the optimum performance occurs with chains of 8–10 carbon
atoms. Atomic force microscopy shows a correlation between pentacene crystalline grain size and transistor performance. 相似文献
50.
The thermal expansion of a fluid combined with a temperature-dependent viscosity introduces nonlinearities in the Navier-Stokes equations unrelated to the convective momentum current. The couplings generate the possibility for net fluid flow at the microscale controlled by external heating. This novel thermomechanical effect is investigated for a thin fluid chamber by a numerical solution of the Navier-Stokes equations and analytically by a perturbation expansion. A demonstration experiment confirms the basic mechanism and quantitatively validates our theoretical analysis. 相似文献