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51.
The spatial distribution of the liquid phase in a typical, partially filled, porous glass (VitraPor #5) has been examined with the aid of magnetic resonance microscopy and field gradient nuclear magnetic resonance diffusometry techniques. The correlation length of the material turned out to be long enough to permit the visualization of the microscopic heterogeneity of the material by magnetic resonance imaging. Contrasts are dominated by transverse relaxation depending on local filling degree, which in turn depends on local microstructure. The bimodal heterogeneity of the latter was also visualized by scanning electron microscopy. The effect of heterogeneity on an effective diffusion coefficient has been examined for polar (water) and nonpolar (cyclohexane) molecules. 相似文献
52.
Shira D. Halperin Hope Fan Stanley Chang Dr. Rainer E. Martin Prof. Robert Britton 《Angewandte Chemie (International ed. in English)》2014,53(18):4690-4693
Fluorination reactions are essential to modern medicinal chemistry, thus providing a means to block site‐selective metabolic degradation of drugs and access radiotracers for positron emission tomography imaging. Despite current sophistication in fluorination reagents and processes, the fluorination of unactivated C? H bonds remains a significant challenge. Reported herein is a convenient and economic process for direct fluorination of unactivated C? H bonds that exploits the hydrogen abstracting ability of a decatungstate photocatalyst in combination with the mild fluorine atom transfer reagent N‐fluorobenzenesulfonimide. This operationally straightforward reaction provides direct access to a wide range of fluorinated organic molecules, including structurally complex natural products, acyl fluorides, and fluorinated amino acid derivatives. 相似文献
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The stannides RE2Au3Sn6 (RE = La, Ce, Pr, Nd, Sm) were synthesized from the elements by arc-melting. Small single crystals were grown by annealing samples in sealed tantalum tubes in an induction furnace with a special annealing sequence. The polycrystalline phases were characterized through their X-ray powder diffraction pattern. The structures of Ce2Au3Sn6, Pr2Au3Sn6, and Nd2Au3Sn6 were refined from single-crystal X-ray diffractometer data. The RE2Au3Sn6 stannides crystallize with the orthorhombic La2Zn3Ge6 type, space group Cmcm. The basic structural building units are Au1@Sn4 tetrahedra and Au2@Sn5 square pyramids. These units are condensed to layers and the structure can be described by a simple stacking of tetrahedral and pyramidal layers with the rare earth cations in between. Temperature dependent susceptibility studies indicate that all rare earth atoms are in the trivalent oxidation state, as their effective magnetic moments match the expected values of the free RE3+ ions. Pr2Au3Sn6 and Nd2Au3Sn6 exhibit antiferromagnetic ordering at TN = 6.3(1) and 6.7(1) K. Investigations of the electrical resistivity of La2Au3Sn6 and Ce2Au3Sn6 confirmed that these compounds are metallic, for La2Au3Sn6 a lower resistivity was observed, in line with the absence of screening unpaired electrons. 119Sn Mössbauer spectra for La2Au3Sn6, Ce2Au3Sn6, Pr2Au3Sn6 and Nd2Au3Sn6 show a complex superposition of three sub-spectra which can be differentiated through their distinctly different quadrupole splitting parameters. The isomer shifts (1.87 to 2.22 mm · s–1) indicate significant s electron density at the tin nuclei. 相似文献
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Bridged 2,3-naphthalocyaninatoruthenium oligomers {[MacRu(L)] n } were synthesized and characterized using solid-state methods. For comparison, soluble t-butyl substituted phthalocyaninatoruthenium oligomers were prepared and their chain length examined by 1H NMR spectroscopy. The powder conductivities of all bridged compounds ([MacRu(L)] n ) were measured and the dependence of the conductivities on the bridging ligands is discussed. 相似文献
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Rainer Haag 《Nachrichten aus der Chemie》1995,43(12):1300-1301
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