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71.
The reaction of metallic bismuth with either tungsten tetrachlorideoxide WOCl4 at 650 K or tungsten tetrabromideoxide WOBr4 at 670 K, respectively, leads to BiX2[W2O2X6] (X = Cl, Br) as black, lustrous crystal needles. The crystal structure determinations (triclinic, P$\bar{1}$ ) show the two isotypic structures to be closely related to Hg0.55[W2O2Cl6] with the presence of 1D‐polymeric W2O2X6 double strands. Dinuclear [Bi2X4]2+ cations are embedded in the host structure via secondary W–X ··· Bi bonds. Unlike the other members of theMy[W2O2X6] structure family, which crystallize monoclinic and show crystallographic equivalent tungsten atoms, BiX2[W2O2X6] has independent tungsten sites. Nevertheless, an assignment of an individual oxidation state to the tungsten atoms within the W2 group (W–W 2.8321(4) Å for X = Cl, 2.8985(4) Å for X = Br) is not possible and a dynamic intervalent state W(IV, V) is assumed. Electrical conductivity measurements for BiCl2[W2O2Cl6] show semi‐conductive behavior with a very small band gap of 70 meV and a high conductivity of around 0.5 Ω–1cm–1 at temperatures above 220 K. A temperature dependence of the activation energy of charge transport is present and interpreted by the Varshni model. 相似文献
72.
Surface spline interpolation when the domain is all of Rd isknown to converge much faster to the data function f than inthe case when the domain is the unit ball. This difference isunderstood to be due to boundary effects which, as will be shown,also affect the size of the surface spline's coefficients. Wepropose a modified form of surface spline interpolation which,to a great extent, overcomes these boundary effects. This modifiedsurface spline interpolant uses only the values of f at thegiven interpolation points. 相似文献
73.
D. Robert Daniels Thomas C. B. McLeish Rama Kant Bryan J. Crosby Ronald N. Young Andrew Pryke Jürgen Allgaier D. J. Groves R. J. Hawkins 《Rheologica Acta》2001,40(5):403-415
We present experiments and theory on the diluted melt dynamics of monodisperse entangled polymers of linear, star and H-shaped
architecture. Frequency-dependent rheological data on a series of progressively diluted linear, star and H-polymers are in
good agreement with a refined tube-model theory that, for H-polymers, combines star polymer melt behaviour at high frequency,
with linear polymer reptation behaviour at low frequencies. Taking into account the effect of dilution via some simple scaling
relations, mild polydispersity and by incorporating the high frequency Rouse modes, we are able to model quantitatively the
entire frequency range. This work suggests a novel rheological route to analysing long chain branching in polymer melts.
Received: 6 April 2000/Accepted: 21 December 2000 相似文献
74.
75.
New heterogeneous catalysts that use oxygen and light to generate singlet oxygen ((1)O2) have been prepared. The catalysts facilitate various types of singlet oxygenation reactions including the Ene reaction, the Diels-Alder reaction, and others. The catalysts are made by stirring a heterogeneous mixture of fullerene-C(60) (dissolved in toluene) with aminomethylated poly(styrene-co-divinylbenzene) beads. Also, catalysts for aqueous photooxidations are made by reacting the initial catalysts with poly(allylamine) to create an outer layer that is more hydrophilic. 相似文献
76.
Clérac R Cotton FA Daniels LM Dunbar KR Murillo CA Pascual I 《Inorganic chemistry》2000,39(4):748-751
The preparation and structures of seven compounds that contain the Cr3(dpa)4(2+) core (dpa = the anion di(2-pyridyl)amide) are reported. The magnetic properties of several have been measured. In each case there are anionic ligands at each end of the Cr3(6+) chain, sometimes identical (2Cl-, 2CCPh-), sometimes different (Cl-, BF4-; Cl-, PF6-). Several of these compounds have a symmetrical arrangement of the three Cr atoms, with the two Cr-Cr distances equal at ca. 2.36 A, while others have an unsymmetrical arrangement. In the most extreme case the two Cr-Cr distances are 2.00 and 2.64 A. The electronic structures and the remarkable flexibility of the Cr3 arrangement are discussed. 相似文献
77.
The noise equivalent power of optical heterodyne detection at 10.6 m has been measured with a method based on Raman-Nath diffraction of a CO2 laser beam. One of the frequency shifted first order diffracted beams is used as the signal radiation. The local oscillator radiation is obtained by splitting off a part of the laser beam incident upon the device used for the acoustooptic diffraction. The signal power can be varied over a large dynamic range by changing the acoustic input power. A study of the probable errors shows that the total error in the NEP measurement is less than 30%. 相似文献
78.
Frank J. Villani Peter J. L. Daniels Claire A. Ellis Thomas A. Mann Kai-Chih Wang 《Journal of heterocyclic chemistry》1971,8(1):73-81
The preparation and properties of four isomeric azadibenzoeycloheptenones 3 and their 10,11-dihydro derivatives 2 are described. The ketones 2 were prepared by cyclization of appropriately substituted phenethylpyridine carboxylic acids and dehydrogenated to 3 . Four monochloro derivatives 24 of the 4-azaketone 2d are also described. 相似文献
79.
A routine fluorimetric procedure is described for the determination of trace amounts of uranium in zircon. It employs the direct extraction of uranyl nitrate with ethyl acetate using phosphate as a retainer for zirconium. Submicrogram amounts or uranium are separated in the presence of 100,000 times the amount of zirconium. The modified procedure has been worked out using synthetic mixtures of known composition and zircon. Results of analyses have an accuracy of 97–98% of the contained uranium and a standard deviation of less than 2.5%. 相似文献
80.