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481.
482.
Katharina Marie Wenz Günter Leonhardt‐Lutterbeck Prof. Dr. Bernhard Breit 《Angewandte Chemie (International ed. in English)》2018,57(18):5100-5104
A new type of ligand, which is able to form axially chiral, supramolecular complexes was designed using DFT calculations. Two chiral monomers, each featuring a covalently bound chiral auxiliary, form a bidentate phosphine ligand with a twisted, hydrogen‐bonded backbone upon coordination to a transition metal center which results in two diastereomeric, tropos complexes. The ratio of the diastereomers in solution is very temperature‐ and solvent‐dependent. Rhodium and platinum complexes were analyzed through a combination of NMR studies, ESI‐MS measurements, as well as UV‐VIS and circular dichroism spectroscopy. The chiral self‐organized ligands were evaluated in the rhodium‐catalyzed asymmetric hydrogenation of α‐dehydrogenated amino acids and resulted in good conversion and high enantioselectivity. This research opens the way for new ligand designs based on stereocontrol of supramolecular assemblies through stereodirecting chiral centers. 相似文献
483.
Ulf Leonhardt Prof. 《Physik in unserer Zeit》2010,41(4):159-159
484.
Brenno A. DaSilveira Neto Gunter Ebeling Valentim E.U. Costa Jairton Dupont 《Tetrahedron》2005,61(46):10975-10982
The reaction of 4,7-dibromo-2,1,3-benzothiadiazole with arylboronic acids (phenyl, 1-naphthyl, 4-methoxyphenyl, 4-chlorophenyl and 4-trifluoromethylphenyl) in the presence of catalytic amounts of a NCP-pincer palladacycle affords photoluminescent π-extended 4,7-diaryl-2,1,3-benzothiadiazoles 4a-e in high yields. These 4,7-diaryl-2,1,3-benzothiadiazoles exhibit high fluorescent quantum yields, high electron affinities and adequate band gap values for testing as OLEDs. The 4,7-bis-naphthyl-2,1,3-benzothiadiazole 4b presents two different lifetimes (bi-exponential decay) due to the presence of two atropisomers. The Sonogashira coupling reaction of 4,7-diethynyl-2,1,3-benzothiadiazole 6 with the corresponding halo-aryl compounds (iodobenzene, 1-bromonaphthalene, 4-iodoanisole, 4-bromo-N,N-dimethylaniline and 2-bromopyridine) afforded the photoluminescent π-extended 4,7-bis-alkynylaryl-2,1,3-benzothiadiazoles 7a-e, also in high yields. These 4,7-diethynyl-2,1,3-benzothiadiazoles also present high fluorescent quantum yields, high electron affinities and adequate band gap values for testing as OLEDs. The 4,7-disubstituted-2,1,3-benzothiadiazoles 4a-e and 7a-e exhibit different electrochemical behavior. The presence of two ethynyl spacers in 2,1,3-benzothiadiazoles 7a-e shifts the reduction potentials to less cathodic values and also results in two well-defined and distinct reduction processes. 相似文献
485.
Gelesky MA Umpierre AP Machado G Correia RR Magno WC Morais J Ebeling G Dupont J 《Journal of the American Chemical Society》2005,127(13):4588-4589
Stable Pd(0) and Rh(0) nanoparticles with small and narrow size distribution can be prepared from relative large and agglomerated transition-metal particles dispersed in 1-n-butyl-3methylimidazolium hexafluorophosphate ionic liquid by simple laser irradiation. The laser irradiation is a complementary method for the generation of stable metal colloids in ionic liquids and also for the regeneration of small-size nanoparticles that may result from their agglomeration after different applications. 相似文献
486.
The design and chemical synthesis of a series of hybrid flexible self-assembling supramolecules utilising both crown ether-naphthalene diimide host-guest chemistry and metalloporphyrin-pyridyl coordination is discussed. The resulting compound structures and dynamics are probed using a variety of techniques, including diffusion ordered NMR spectroscopy (DOSY) and cold-spray ionisation mass spectrometry (CSI-MS). 相似文献
487.
Glasses with the compositions 50.9 SiO2 · 20.8 Al2O3 · (20.8 ? x) MgO· × ZnO · 3.7 TiO2 · 3.7 ZrO2 with x = 0, 2.3, 4.6 and 9.3 were annealed at temperatures in the range from 850 to 1100 °C. Depending on temperature, high- or low-quartz solid solutions, magnesium aluminosilicate, mullit and spinel precipitated. These glass–ceramics exhibit excellent mechanical properties and are potential candidates for applications in micromechanics or as hard disc substrate.The larger the ZnO concentration, the lower is the glass transition temperature. Also microhardnesses and Young’s moduli increased with increasing ZnO concentration. The nucleation temperature was of minor importance. To achieve good mechanical properties, the initially formed high-quartz phase must transform to the corresponding low-quartz phase. This occurs if the quartz phase contains only minor MgO or ZnO concentrations, which can be achieved by increasing the annealing times or temperature. Then MgO, ZnO and Al2O3 occur as separate spinel or gahnite phase. 相似文献
488.
Yuri Grin Walter Schnelle Olga Sichevich Ralf Müllmann Gunter Kotzyba 《Journal of solid state chemistry》2003,176(2):567-574
The title compound was prepared from the elements by reaction in a sealed tantalum tube at 1320 K followed by slow cooling to 970 K or, alternatively, in glassy carbon crucibles with HF melting. The crystal structure of Eu5Ga9 was refined from single-crystal data: Cmcm, a=4.613(1) Å, b=10.902(3) Å, c=26.097(6) Å, Z=4, RF=0.036, 811 structure factors and 46 variables. The structure is described as a three-dimensional network formed by gallium atoms with europium atoms embedded in the cavities. The bonding analysis (LMTO, ELF) confirmed this representation of the structure. Magnetic susceptibility measurements show Curie-Weiss behavior above 60 K with a magnetic moment per Eu atom of 8.12(1) μB, indicating divalent europium. Eu5Ga9 orders antiferromagnetically at 19.0(5) K with re-ordering at 6.0(5) K. The electrical resistivity shows a metallic temperature dependence and magnetic scattering. 151Eu Mössbauer spectroscopic experiments are compatible with divalent europium and show complex magnetic hyperfine field splitting below the ordering temperature. 相似文献
489.
Carmai Seto Kevin P. Bateman Berton Gunter 《Journal of the American Society for Mass Spectrometry》2002,13(1):2-9
Standard approaches to development of liquid chromatography-mass spectrometry (LC-MS) methods, either ion-pairing or reversed-phase liquid chromatography, have been through trial and error or intentional variation of experimental factors. These approaches to method optimization fail to take into account interactions between experimental factors and therefore the results may not be optimal for the combination of experimental factors. Another approach to optimization is through the use of chemometrics. Chemometric approaches can be more efficient than trial and error or intentional variation because chemometrics make use of multivariate designs; experimental factors are varied simultaneously at the various levels. Therefore chemometrics can take into account interactions between factors. The goal of this study was to develop a generic ion-pair LC-MS method for the analysis of acidic compounds using a chemometric approach called design of experiments (DOE). Four acidic compounds which cover three classes of acidic functional groups: 1-naphthyl phosphate (1), 1-naphthalenesulfonic acid (2), 2-naphthalenesulfonic acid (3), and (1-naphthoxy)acetic acid (4) were used as model compounds to develop the generic method. This study illustrates that LC-MS conditions can be optimized efficiently with minimal amount of experimentation using a chemometric approach to experimental design. 相似文献
490.
CoIn3, RhIn3, and IrIn3 were synthesized by reacting the elements in sealed tantalum tubes at 1170 K and subsequent annealing at 770 K. The structures of the three compounds (FeGa3 type, space group P42/mnm) were refined from single crystal X-ray data: a = 682.82(6), c = 709.08(7) pm, wR2 = 0.0407, 397 F2 values for CoIn3, a = 698.28(8), c = 711.11(9) pm, wR2 = 0.0592, 418 F2 values for RhIn3, and a = 699.33(5), c = 719.08(5) pm, wR2 = 0.0625, 482 F2 values for IrIn3 with 16 parameters for each refinement. The structures may be considered as an intergrowth of tungsten-like building blocks of indium atoms and AlB2-like slabs of compositions In&Co, In&Rh, and In&Ir, respectively. These are compared with the related intergrowth variants found for compounds with ordered U3Si2 and Zr3Al2 type structure. Semi-empirical band structure calculations for RhIn3 reveal low density-of-states (DOS) at the Fermi level and negative Rh–Rh crystal orbital overlap populations (COOP) indicating antibonding Rh–Rh interactions. The bonding characteristics of CoIn3, RuIn3, and IrIn3 are similar to RhIn3. Magnetic susceptibility measurements of compact polycrystalline samples of CoIn3, RhIn3, and IrIn3 indicate weak Pauli paramagnetism. 相似文献