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71.
Michael Chariss Andrea Zickgraf Heike Stenger Elmar Bru Cristelle Desmarquet Martin Drger Silke Gerstmann Dainis Dakternieks James Hook 《Polyhedron》1998,17(25-26)
44 members of thecompound series Ph4−nMRn (M=Si, Ge, Sn, Pb; R=o-, m-, p-Tol; n=0–4) were synthesized (15 newcompounds). The crystal structures of Ph3Sn (o-Tol) and PhSn (o-Tol)3 were determined and compared to 16 known structures. Subject to the distanced (M–C), an interplay between through-space π–π repulsion and π–σ attraction leads to either elongated or compressed tetrahedral geometry. 29 Si-, 119 Sn- and 207 Pb-NMR chemical shifts were determined in solution and in the solid state. 73 Ge chemical shifts were measured only in solution. Anupfield or downfield sagging of the chemical shifts along each series is rationalized in terms of a π–σcharge transfer which is constrained by torsion of the aromatic groups. 相似文献
72.
Thiobromo Complexes of Arsenic and Antimony. Preparation and Crystal Structures of (PPh4)2[As2SBr6] · CH2Br2 and (PPh4)2[Sb2SBr6] · CH2Br2 (PPh4)2[As2SBr6] · CH2Br2 is formed by the reaction of As2S3, PPh4I and HI in dibromomethane. It can also be obtained, as well as (PPh4)2[Sb2SBr6] · CH2Br2, from (PPh4)2[As2Br8] and (PPh4)3[Sb2Br9], respectively, with bistrimethylsilylsulfide. The crystal structures of the title compounds were determined by X-ray diffraction. They are isotypic with (PPh4)2[As2SCl6] · C2H4Cl2. In the anions [M2SBr6]2? the M atoms (As or Sb) have a distorted octahedral coordination, the two octahedra share acommon face with one bridging S and two Br atoms; the lone electron pairs occupy the trans positions to the S atom. Crystal data: triclinic, space group P1 , Z = 2; (PPh4)2[As2SBr6] · CH2Br2, a = 119.1, b = 1203.6, c = 2067.5 pm α= 94.89, β = 97.78, γ = 112.20°, 3046 independent observed reflexions, R = 0.083; (PPh4)2[Sb2SBr6] · CH2Br2, a = 1198.9, b = 1224.3, c = 2085.5pm, α = 95.04, β = 98.48, γ = 112.13°C, 2380 reflexions, R = 0.079. 相似文献
73.
74.
A cylindrical chemosorptive denuder in series with a glass fibre filter has been evaluated for sampling toluene diisocyanate (TDI) aerosols. The sampler is designed for measuring personal exposure to diisocyanates. Several denuder coatings and derivatising reagents were investigated. Dimethylpolysiloxane (SE-30) and 5% phenyl dimethylpolysiloxane (SE-54) with either dibutylamine (DBA) or dipentylamine (DPeA) as derivatising reagents yielded the lowest vapour breakthrough (the amount (%) of the vapour that passes through the denuder), close to values predicted by theory. Immobilisation of the SE-30 denuder coating by in-situ cross-linking yielded comparable results. With an SE-30/DBA-coated denuder operating within an airflow range of 100–500 mL min–1, the phase separation was shown to be consistent with theoretical predictions derived by use of the Gormley–Kennedy equation. This provides a means of calculating the vapour breakthrough and correcting experimentally obtained values with regard to vapour–particulate phase distribution, suggesting that the denuder can provide accurate phase-distribution measurements. The SE-30/DBA denuder can be used over a concentration range spanning nearly six orders of magnitude. Its capacity is sufficient to perform 15-min exposure measurements of a TDI aerosol with air concentrations as high as 1,700 g m–3, 40 times higher than the Swedish occupational exposure limit (OEL). At the other end of the range, the estimated limit of detection (LOD) was less than 2 ng m–3 for both the vapour and the aerosol phases when LC–ESI–MS–MS was used for chemical analysis.Electronic Supplementary Material Supplementary material for this article is available at 相似文献
75.
The crystal structure of the κ-carbide in the FeWC system has been refined from neutron powder diffraction data using the Rietveld profile analysis method. κ-(FeWC) is isostructural with κ-(CoWC); space group ; unit cell dimensions a = 7.7982(2)Å, c = 7.8298(4) Å. The structure refinement indicates substitution at two of the tungsten sites, and 46% vacancies at one of the carbon sites. The composition corresponds to the formula Fe3+xW10?xC4?y, with x = 0.57(3) and y = 0.46(1). 相似文献
76.
Gerhard Schomburg Alfred Deege Heike Hinrichs Eduard Hübinger Heribert Husmann 《Journal of separation science》1992,15(9):579-584
Methods of alkylation of α-, β- and γ-cyclodextrins have been optimized with regard to the parameters of reaction, degree of alkylation and yields. The analysis of the reaction mixtures and of the isolated single species has been performed by high temperature GC and HPLC. The phase systems of the preferably applied HPLC have been carefully adjusted by variation of both the stationary and mobile phases to the very different hydrophobicities of the various alkylated CD species which have been synthesized. Several partially or fully alkylated CD species were isolated from preparative scale HPLC separations in high purity. 相似文献
77.
The chiral separation of halogenated amino acids by ligand-exchange CE is described. Halogenated amino acids attracted increasing interest in recent years because of their physiological activities. Different chiral selectors, as there are L-4-hydroxyproline, L-histidine, and N-alkyl derivatives of L-4-hydroxyproline in form of their copper(II) complexes, are compared for their chiral recognition ability for halogenated amino acids. The influence of various parameters, such as selector concentration, pH, organic modifier, and field strength, on the resolution was investigated. All halogenated amino acids investigated were baseline-separated under optimized conditions. 相似文献
78.
Flow vacuum thermolysis (FVT) of thiophene-2,3-dicarboxylic anhydride () in the presence of 2,3-dimethylbutadiene () gives, in addition to 5,6-dimethylthianaphthene (). small quantities of a dihydrodimethylthianaphthene () and another dimethylthianaphthene () which is probably also formed by dehydrogenation of with chloranil. The partial structures of these minor products are consistent with their being formed by a [2+2]-cycloaddition between and an intermediate aryne, 2,3-didehydrothiophene (), followed by a rearrangement of the resulting adduct and dehydrogenation. FVT of in the presence of 2,5- () or 3,4-dimethylthiophene () also gave a mixture of the dimethylthianaphthenes (, ) which can be rationalized as arising by a [4+2]- and two [2+2]-cycloadditions of the aryne to the thiophenes with subsequent desulfurization. The lack of equilibration of the products , and , was demonstrated and their origin as a function of the structure and reactivity of the aryne discussed. 相似文献
79.
Busby M Gabrielsson A Matousek P Towrie M Di Bilio AJ Gray HB Vlcek A 《Inorganic chemistry》2004,43(16):4994-5002
The nature and dynamics of the lowest excited states of fac-[Re(I)(L)(CO)(3)(phen)](+) and fac-[Re(I)(L)(CO)(3)(5-NO(2)-phen)](+) [L = Cl(-), 4-ethyl-pyridine (4-Etpy), imidazole (imH); phen = 1,10-phenanthroline] have been investigated by picosecond visible and IR transient absorption spectroscopy in aqueous (L = imH), acetonitrile (L = 4-Etpy, imH), and MeOH (L = imH) solutions. The phen complexes have long-lived Re(I) --> phen (3)MLCT excited states, characterized by CO stretching frequencies that are upshifted relative to their ground-state values and by widely split IR bands due to the out-of-phase A'(2) and A"nu(CO) vibrations. The lowest excited states of the 5-NO(2)-phen complexes also have (3)MLCT character; the larger upward nu(CO) shifts accord with much more extensive charge transfer from the Re(I)(CO)(3) unit to 5-NO(2)-phen in these states. Transient visible absorption spectra indicate that the excited electron is delocalized over the 5-NO(2)-phen ligand, which acquires radical anionic character. Similarly, involvement of the -NO(2) group in the Franck-Condon MLCT transition is manifested by the presence of an enhanced nu(NO(2)) band in the preresonance Raman spectrum of [Re(I)(4-Etpy)(CO)(3)(5-NO(2)-phen)](+). The Re(I) --> 5-NO(2)-phen (3)MLCT excited states are very short-lived: 7.6, 170, and 43 ps for L = Cl(-), 4-Etpy, and imH, respectively, in CH(3)CN solutions. The (3)MLCT excited state of [Re(I)(imH)(CO)(3)(5-NO(2)-phen)](+) is even shorter-lived in MeOH (15 ps) and H(2)O (1.3 ps). In addition to (3)MLCT, excitation of [Re(I)(imH)(CO)(3)(5-NO(2)-phen)](+) populates a (3)LLCT (imH --> 5-NO(2)-phen) excited state. Most of the (3)LLCT population decays to the ground state (time constants of 19 (H(2)O), 50 (MeOH), and 72 ps (CH(3)CN)); in a small fraction, however, deprotonation of the imH.+ ligand occurs, producing a long-lived species, [Re(I)(im.)(CO)(3)(5-NO(2)-phen).-]+. 相似文献
80.
Anders Melin 《偏微分方程通讯》2013,38(7):677-766