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排序方式: 共有2369条查询结果,搜索用时 15 毫秒
31.
Aisha I. Ibrahim 《Transition Metal Chemistry》1994,19(6):561-563
Summary By the interaction of anhydrous CoBr2 or CoBr2·2THF with different sodium aryloxides, a new series of complexes of general formula Na2[Co(OAr)4]·nTHF (OAr =o-nitro,o-chloro,o-bromo,m-chloro,p-bromo, 2,4-dichloro, 2,6-dichloro, or 2,4-dimethylphenoxide;n = 1, 3, 4 or 5) were prepared and characterized by physicochemical means. The electronic spectra and magnetic measurements suggest a tetrahedral geometry for cobalt(II). Heating the complexes led to reversible loss of THF with an accompanying colour change. 相似文献
32.
Ibrahim H. A. Badr 《Mikrochimica acta》2005,149(1-2):87-94
Membrane electrodes based on 2,2-dithiobis(benzothiazole), DTBBT, as a neutral carrier for silver ions are described. Silver-selective membrane electrodes formulated with 2wt% DTBBT ionophore and 50mol% TFPB in an FPNPE plasticized poly (vinyl chloride) exhibited near-Nernstian responses towards silver ions (60.3±0.5mVdecade–1) over a wide silver ion activity range of 0.83µM to 94mM. Increasing the amount of anionic sites, TFPB, to 100 or 150mol% (relative to the DTBBT weight) resulted in super-Nernstian responses toward silver ions. Membrane electrodes prepared using a low dielectric constant plasticizer, however, exhibited sub-Nernstian responses. Polymer membrane electrodes with optimal composition (i.e., 2wt% DTBBT, 50mol% TFPB in FPNPE plasticized poly(vinyl chloride)) exhibited high potentiometric selectivity towards silver ions over alkali, alkaline earth, transition metal ions, as well as heavy metal ions such as Hg2+ and Pb2+. A good correlation was found between the potentiometric selectivity coefficients and the change in the UV-visible spectra of the ionophore upon exposure to different metal ions. The overall performance of the silver-selective membrane electrodes based on DTBBT ionophore, which is available at low cost, was found to be comparable to the performance of silver electrodes prepared with Fluka silver ionophore-IV. A DTBBT-based silver electrode was used as an indicator electrode for titrations of silver ions using standard sodium chloride solutions. Sharp inflections occur at the end point, and the data obtained showed 99.4% recovery with a standard deviation of 0.7% (n=3). In addition, the applicability of the DTBBT-based silver-selective electrode is illustrated by measuring the silver concentrations in natural water spiked with silver nitrate and by analyzing the silver in electroplating wastewater samples. The results obtained utilizing a DTBBT-based silver electrode showed very good agreement with the standard methods of analysis. 相似文献
33.
Ibrahim MS 《Fresenius' Journal of Analytical Chemistry》2000,367(2):189-194
The electrochemical behavior of lumazine (LMZ), an important antibacterial agent, has been studied at the hanging mercury drop electrode (HMDE). The nature of the process taking place at the HMDE was clarified. Its adsorption behavior at HMDE has been studied by using a.c and cyclic voltammetry (CV). Both the molecule and its reduced product appeared to be adsorbed at the surface of the electrode. Controlled adsorptive accumulation of LMZ on the HMDE provides the basis for the direct stripping measurement of that compound in the subnanomolar concentration level. Experimental and instrumental parameters for the quantitative determination were optimized. Phase-selective a.c voltammetry provided the best signal and gave a detection limit of 0.15 microg L(-1) (9.0 x 10(-10) mol/L) LMZ in aqueous solution. Molecules or ions which may interfere were studied. 相似文献
34.
Six X-ray crystal structures are reported, all containing substituted triphenylmethanol derivative 4 either alone or as its mono or bis(chromium tricarbonyl) complexes. All four chromium complexes studied crystallize with two independent molecules in the crystallographic asymmetric unit. It is demonstrated that from the X-ray crystal structure of the acentric racemic (+/-)-(1pR,1' 'R)(1pS,1' 'S)-[Cr(CO)(3)(eta(6)-t-BuC(6)H(3)(CMeOMe)CPh(2)OH)], (+/-)-3, it is possible to deduce the 4-fold helical structure of the chiral (-)-(1pR,1' 'R) isomer, (-)-3. The bimetallic derivatives demonstrate the ability to control intermolecular interactions by the positioning of relative stereochemistry. 相似文献
35.
Mustafa R. Ibrahim Zacharia A. Fataftah Paul von Ragu Schleyer Peter D. Stout 《Journal of computational chemistry》1987,8(8):1131-1138
Sets of hydrogen molecule equivalents have been developed which permit the calculation of hydrogenation of different types of carbon-carbon bonds from ab initio total energies (3-21G and 6-31G* basis sets, and, to a more limited extent, for MP2/6-31G* data) of reactants and products. The calculated enthalpies of hydrogenation are in good agreement with experiment for unstrained molecules, with average errors on the order of 2 kcal/mol. The 6-31G* equivalents allow the enthalpies for strained molecules to be calculated accurately, but the 3-21G equivalents do not. The equivalents for both basis sets have been tested by calculating the enthalpies of hydrogenation of carbon-carbon bonds in nitrogen- and oxygen-containing organic molecules, free radicals, and classical carbocations. The results are in good agreement with experiment in most cases. 相似文献
36.
3-[1′(1′H)-Substituent-pyrazol-5′-yl]benzo[5,6]coumarins and 3-(1′,2′-oxazol-5′-yl)benzo[5,6]coumarin were prepared via condensation of 3-(2′-formyl-1′-chlorovinyl)benzo[5,6] coumarin with hydrazine derivatives or hydroxylamine.Reaction of 3-[1′(1′H)-pyrazol-5′-yl]benzo[5,6]coumarin with alkyl halides,olefinic compunds or acid chlorides are described. 相似文献
37.
We report experimentally measured cross sections for pressure broadening of ammonia inversion transitions by J=0, ortho-D2 at temperatures of 18-40 K. These measurements were made in a quasiequilibrium cell using the collisional cooling technique. Cross sections for broadening of the metastable (J,K)=(1, 1), (2, 2) and (3, 3) inversion transitions ranged from 67.5 A2 for (1, 1) at 20.0 K to 100.1 A2 for (3, 3) at 25.0 K. The J=0, ortho-D2 cross sections were found to be consistently larger than previously measured cross sections for low temperature broadening of NH3 by both He and H2. 相似文献
38.
Ayoko Godwin Adefikayo Iyun Johnson Femi El-Idris Ibrahim Faskari 《Transition Metal Chemistry》1992,17(1):46-49
Transition Metal Chemistry - The kinetics of the silver(I) ion catalysed reduction of peroxodisulphate by 12-tungstocobaltate(II) anion in aqueous HC1O4 has been studied. Although the reaction in... 相似文献
39.
Mohamed M. Shoukry Ibrahim M. Kenawy Ibrahim H. El-Haj 《Transition Metal Chemistry》1991,16(6):637-640
Summary The formation and equilibria of the binary and ternary palladium(II) complexes of diethylenetriamine (dien) with other selected amines have been investigated. The results of pH titration measurements allowed the calculation of equilibrium constants, characteristic for the binary and ternary complexes formed. The concentration distribution of various complex species was evaluated and the chelation mode ascertained by conductivity measurements. 相似文献
40.
The ionization of six compounds of bis-phenolic amides was studied spectrophotochemically in DMF-water mixture. The compounds showed two pKa values in the range of 5.97-7.32 for pKa1 and 7.61-8.44 for pKa2. The obtained values of Ka were normalized using the distribution diagrams of the different species and found to be in the range of 5.81-7.42 for pKa1 and 7.48-8.27 for pKa2. 相似文献