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41.
The brown crystals of [PMePh3]2[Se2Br6] ( 1 ) and red crystals of [PMePh3]2[SeBr6(SeBr2)2] ( 2 ) were obtained when selenium and bromine reacted in the solution of acetonitrile in the presence of methyltriphenylphosphonium bromide. The crystal structures of 1 and 2 has been determined by the X‐ray methods and refined to R = 0.0373 for 2397 reflections and 0.0397 for 3417 reflections, respectively. The salt 1 crystallizes in the monoclinic space group P21/n with the cell dimensions a = 13.202(5) Å, b = 11.954(4) Å, c = 13.418(6) Å, β = 93.08(4)° (193(2)). The crystals of 2 are triclinic, space group with the cell dimensions a = 10.266(3) Å, b = 11.311(3) Å, c = 11.619(2) Å, α = 108.87(2)°, β = 105.72(2)°, γ = 99.40(2)° (193(2) K). In the solid state structure of 1 the dinuclear hexabromo‐diselenate(II) anion is centrosymmetric and consists of two distorted almost square planar SeBr4 units sharing a common edge through two μ‐bridging Br atoms. The terminal SeII–Br bonds are 2.3984(11) and 2.4273(11) Å, whereas the bridging μBr–SeII bonds are 2.7817(11) and 2.9081(12) Å. In the solid state the trinuclear [SeBr6(SeBr2)2]2? anion of 2 is centrosymmetric too and contains a nearly regular [SeBr6] octahedron where the four equatorial bromo ligands each have developed bonds to the SeII atoms of the SeBr2 molecules. The contacts between the bridging bromo and the SeII atoms of the SeBr2 molecules are 3.0603(15) and 3.1043(12) Å, and can be interpreted as bonds of the donor‐acceptor type with the bridging bromo ligands as donors and the SeBr2 molecules as acceptors. The SeIV–Br distances are in the range 2.5570(9)–2.5773(11) Å and the SeII–Br bond lengths in coordinated SeBr2 molecules – 2.3411(12) and 2.3421(10) Å. 相似文献
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Polarized IR spectra of five benzene derivatives (four of C2v symmetry and one of D2h symmetry) have been recorded using the stretched polymer method. It has been found that the values of the dichroic ratios depend systematically on the symmetry class of the vibration in question. The IR-active vibrations can thus be unambiguously divided into the correct symmetry classes. The general validity of the method, as well as its value for vibrational analysis, is discussed. 相似文献
45.
Reisman SE Ready JM Weiss MM Hasuoka A Hirata M Tamaki K Ovaska TV Smith CJ Wood JL 《Journal of the American Chemical Society》2008,130(6):2087-2100
An efficient and highly stereoselective total synthesis of the natural product (+/-)-welwitindolinone A isonitrile (1) is described. The bicyclo[4.2.0]octane core of 1 was established by a regio- and diastereoselective [2+2] ketene cycloaddition. The C12 quaternary center and vicinal stereogenic chlorine were installed in a single operation with excellent stereocontrol via a chloronium ion mediated semipinacol rearrangement. Described strategies for construction of the spiro-oxinole include a SmI2-LiCl mediated reductive cyclization and a novel anionic cyclization that simultaneously constructs the spiro-oxindole and vinyl isonitrile moieties. 相似文献
46.
Dispersion Theory of Liquids Containing Optically Linear and Nonlinear Maxwell Garnett Nanoparticles 总被引:2,自引:0,他引:2
Kai-Erik Peiponen Martti O. A. M#xE;kinen Jarkko J. Saarinen Toshimitsu Asakura 《Optical Review》2001,8(1):9-17
Kramers-Kronig relations and sum rules for effective linear permittivity of the Maxwell Garnett liquid-nanosphere system were obtained using complex analysis and general expression of the effective permittivity. When reflectance from optically linear and nonlinear Maxwell Garnett nanoparticles was calculated it was observed that the reflectance, in the case of attenuated total reflection, depends on the fill fraction of the nanospheres and their nonlinear susceptibility. According to simulations a good sensitivity of the nonlinear contribution on the reflectance can be obtained by using a probe wavelength corresponding to the resonance frequency of the nanosphere system. In Kretchmann#x0027;s configuration it was observed that the surface-plasmon-resonance angle depends on the fill fraction and on the intensity of the incident light. By using reflectance, it is possible to detect optically nonlinear nanospheres in liquids. 相似文献
47.
A series of hydroxyphenylketimines, of which 15 are new, was synthesized in methanol at high temperature (200°C) using a sealed steel reactor. This reaction setup especially enhances the synthesis of 2‐hydroxyphenylketimines, with yields up to six times higher than those obtained with the conventional acid‐catalyzed method under refluxing conditions. In fact, some imines were achievable only by the autoclave method. 相似文献
48.
Catechol and endogenous catechol derivatives are readily methylated by catechol O-methyltransferase (COMT). In contrast, many catechol derivatives possessing electronegative substituents are potent COMT inhibitors. The X-ray structure of the active site of COMT suggests that the methylation involves a lysine as a general base. The lysine can activate one of the catecholic hydroxyl groups for a nucleophilic attack on the active methyl group of the coenzyme S-adenosyl-l-methionine (AdoMet). We studied the effect of dinitrosubstitution of the catecholic ring at the semiempirical PM3 level on the methylation reaction catalysed by COMT. The electronegative nitro groups make the ionized catechol hydroxyls less nucleophilic than the corresponding hydroxyl groups of the non-substituted catechol. As a consequence, dinitrocatechol is not methylated but is instead a potent COMT inhibitor. The implications of this mechanism to the design of COMT inhibitors are discussed. 相似文献
49.
Detection of Sea Surface Temperature (SST) Using Infrared Band Data of Advanced Very High Resolution Radiometer (AVHRR) in the Gulf of Finland 总被引:1,自引:0,他引:1
Yuanzhi Zhang Jouni Pulliainen Sampsa Koponen Martti Hallikainen 《International Journal of Infrared and Millimeter Waves》2002,23(10):1407-1412
This paper presents the detection of sea surface temperature (SST) in the Gulf of Finland using infrared band data of Advanced Very High Resolution Radiometer (AVHRR). AVHRR imagery is evaluated as a main data source for monitoring SST as a measure of upwelling's dynamic. Sea surface effects (SSE), however, cause a temperature difference between the sea surface skin and water below the surface. Therefore, SSE is taken into account as one of the major error factors in the SST esimation. Further studies will be investigated using both AVHRR and MODIS in the future. 相似文献
50.