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71.
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2-Pyridinamine Adducts of Transition Metal Bis(acetylacetonates) and their Reactions. Hydrogencarbonate as a Chelating Ligand in cis-(Ampy)2Co(acac)(HCO3) The reaction of cobalt(II) salts, acetylacetone (acacH), 2-pyridinamine (Ampy), and the carbon dioxide of the air in methanol affords a mixture of (Ampy)2Co(acac)2( II ) and (Ampy)2Co(CO3)(H2O)2. On heating in toluene, appropriately in the presence of carbon dioxide, these complexes are converted into cis-(Ampy)2Co(acac)(HCO3) ( III ). Characteristic of compound III is a four-membered ring with the hydrogencarbonate as a bidentate ligand. The two Co? O distances are distinctly different (215.9 and 224.4 pm). In the complexes II and III 2-pyridinamine is a bidentate ligand coordinating by the endo-nitrogen. The Co-n-N bond lengths vary between 210.9 and 225.3 pm. Reasons are both the different trans-influence of the hydrogencarbonate or the acetylacetonato donor atoms and the π-interaction between cobalt(II) and the pyridine ring. This interaction is more significant in the cis-complex III . II and III are stabilized by a system of N? H …? O- and O? H …?O-bridges. With nickel(II) complexes analogous to II and III were obtained, while only the type II was characterized for manganese( II ). 相似文献
73.
Yunchang Fan Meilan Chen Fawzi El-Sepai Yan Zhu Mingli Ye 《Analytica chimica acta》2009,650(1):65-654
A simple analytical method, based on the coupling of ionic liquid-based extraction with high performance liquid chromatography (HPLC), is developed for the determination of Sudan dyes (I, II, III and IV) and Para Red in chilli powder, chilli oil and food additive samples. Two ionic liquids (ILs), 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]) and 1-octyl-3-methylimidazolium hexafluorophosphate ([C8mim][PF6]), were compared as extraction solvents; experiments indicated that the latter possesses higher recoveries for each analyte. Parameters related to extraction of Sudan dyes and Para Red were also optimized. Under the optimal conditions, good reproducibility of extraction performance was obtained, with the relative standard deviation (RSD) values ranging from 2.0% to 3.5%. The detection limits of Sudan dyes and Para Red (LOD, S/N = 3) were in the range of 7.0-8.2 μg kg−1 for chilli powder and 11.2-13.2 μg L−1 for chilli oil and food additive. The recoveries were in the range of 76.8-109.5% for chilli powder samples and 70.7-107.8% for chilli oil and food additive samples. 相似文献
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Particulate composites of NiFe2O4 (NFO) and Pb0.93La0.07 (Zr0.60Ti0.40) O3 (PLZT) were synthesized by solid-state reaction technique. Structure and surface morphological studies were carried out using X-ray diffraction and scanning electron microscopy techniques, respectively. Frequency dependent variation of dielectric constant (), loss tangent (tan δ) and ac resistivity for (x) NFO + (1−x) PLZT composites in the range 100 Hz–5 MHz at room temperature were studied. The temperature dependence of dielectric constant (′), loss tangent (tan δ) was studied in wide temperature range of measurement at fixed frequencies. Also DC resistivity measurements were carried out in the temperature range of 300 K–923 K. Structural, dielectric and electrical properties show notable change due to presence of magnetostrictive NFO phase along with PLZT. 相似文献
77.
We study depth properties of a general class of random recursive trees where each node i attaches to the random node \begin{align*}\left\lfloor iX_i\right\rfloor\end{align*} and X0,…,Xn is a sequence of i.i.d. random variables taking values in [0,1). We call such trees scaled attachment random recursive trees (sarrt). We prove that the typical depth Dn, the maximum depth (or height) Hn and the minimum depth Mn of a sarrt are asymptotically given by Dn ~μ‐1 log n, Hn ~ αmax log n and Mn ~ αmin log n where μ,αmax and αmin are constants depending only on the distribution of X0 whenever X0 has a density. In particular, this gives a new elementary proof for the height of uniform random recursive trees Hn ~ elog n that does not use branching random walks.© 2011 Wiley Periodicals, Inc. Random Struct. Alg., 2011 相似文献
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El-Yazbi FA Hammud HH Assi SA 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,68(2):275-278
A derivative spectrophotometric method was developed for the assay of a ternary mixture of aspirin (ASP), paracetamol (PAR) and salicylic acid (SAL). The method is based on the use of the first and second derivatives of the ratio spectra and measurement at zero-crossing wavelengths. The ratio spectra were obtained by dividing the absorption spectrum of the mixture by that of one of the components. The concentration of the other components are then determined from their respective calibration curves treated similarly. The described method was applied for the determination of these combinations in synthetic mixtures and dosage forms. The results obtained were accurate and precise. 相似文献