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51.
31P solid-state nuclear magnetic resonance (NMR) spectra of 12 metal-containing selenophosphates have been examined to distinguish between the [P(2)Se(6)](4-), [PSe(4)](3-), [P(4)Se(10)](4-), [P(2)Se(7)](4-), and [P(2)Se(9)](4-) anions. There is a general correlation between the chemical shifts (CSs) of anions and the presence of a P[bond]P. The [P(2)Se(6)](4-) and [P(4)Se(10)](4-) anions both contain a P[bond]P and resonate between 25 and 95 ppm whereas the [PSe(4)](3-), [P(2)Se(7)](4-), and [P(2)Se(9)](4-) anions do not contain a P[bond]P and resonate between -115 and -30 ppm. The chemical shift anisotropies (CSAs) of compounds containing [PSe(4)](3-) anions are less than 80 ppm, which is significantly smaller than the CSAs of any of the other anions (range: 135-275 ppm). The smaller CSAs of the [PSe(4)](3-) anion are likely due to the unique local tetrahedral symmetry of this anion. Spin-lattice relaxation times (T(1)) have been determined for the solid compounds and vary between 20 and 3000 s. Unlike the CS, T(1) does not appear to correlate with P-P bonding. (31)P NMR is also shown to be a good method for impurity detection and identification in the solid compounds. The results of this study suggest that (31)P NMR will be a useful tool for anion identification and quantitation in high-temperature melts. 相似文献
52.
R. Hoelzl Christian Hoelzl Ludwig Kotz Lazlo Fabry 《Accreditation and quality assurance》1998,3(5):185-188
Inductively coupled plasma mass spectrometry (ICP-MS) and high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS)
are powerful methods of determining metallic impurities in the low- and sub-ppt level in process media such as ultra-pure
water used in semiconductor and wafer manufacturing. By using mass spectrometers for analysis, an isotope dilution analysis
(IDMS) is possible. The reproducibility of an IDMS is unmatched. For concentration levels near the instrument detection limit
a novel method is reported to find the optimal amount of isotopic spike solution. This optimal value can be derived by the
law of propagation of uncertainty combined with the Poisson statistics of the measured number of counts. Generally, an excess
of isotopic spike solution should be used to provide results of lowest possible uncertainty. The results are presented in
a diagram for easy practical use.
Received: 14 October 1997 · Accepted: 13 February 1998 相似文献
53.
[reaction: see text] The photochemistry of N-acyl-5,7-dinitroindoline (1) was studied in acetonitrile using nanosecond time-resolved infrared (TRIR) spectroscopy. Upon photolysis, two nearly but not completely overlapping sets of transient IR bands are observed that are assigned to two non-interconvertible conformers of mixed acetic nitronic anhydride 7. While syn-7 reverts rapidly to 1, anti-7 is long-lived and is able to acylate amines. Results of density functional theory calculations support conclusions based on experimental TRIR data. 相似文献
54.
Michael Schaefer Christian N?ther Wolfgang Bensch 《Monatshefte für Chemie / Chemical Monthly》2004,27(7):461-470
Yellow crystals of the title compound were obtained under solvothermal conditions reacting elemental Zn, Sb, and S in a solution of tris(2-aminoethyl)amine (=tren) and water. The compound crystallises in the monoclinic space group P21/c with a=13.0247(7), b=22.308(2), c=12.1776(6) Å, and =105.352(6)°. In the structure of [Zn(tren)]2Sb4S8·0.75 H2O two [Zn(tren)]2+ cations are bound to the [Sb4S8]4– anion via S atoms. The Zn2+ ions are in a trigonal bipyramidal environment of four N atoms of the tetradentate tren ligand and one S atom of the [Sb4S8]4– anion. The anion is formed by SbS3 and SbS4 units which share common corners and edges. The interconnection mode yields three different non-planar Sb2S2 heterorings. The shortest intermolecular Sb–S distance amounts to about 3.7Å, and taking this long separation into account undulated chains running along [001] are formed with the water molecules residing in the pocket-like cavities. Upon heating the compound decomposes in one step starting at about 240°C. The final decomposition product was identified as ZnS and Sb2S3 by X-ray powder diffractometry. Additionally, spectroscopic data as well as synthetic procedures for [Zn(tren)]2Sb4S8·0.75 H2O are reported. 相似文献
55.
56.
We have chemically prepared a sample of antiferromagnetic alpha-Fe2O3 nanoparticles by a gel-sol technique. M?ssbauer spectra of the as-prepared sample showed that superparamagnetic relaxation was suppressed due to strong magnetic interparticle interactions even at room temperature. However, subsequent grinding of the sample by hand in a mortar for some minutes resulted in fast superparamagnetic relaxation of some of the particles. The effect was even more dramatic if the alpha-Fe2O3 powder was ground for a longer time or together with nonmagnetic eta-Al2O3 nanoparticles. Similar effects were found after low-energy ball milling. Thus it is found that the agglomeration of the nanoparticles during preparation under wet conditions results in strong magnetic interparticle interaction, but a relatively gentle mechanical treatment is sufficient to break up the agglomerates, resulting in much weaker interactions. We show that these effects can also be seen when a soil sample containing magnetic nanoparticles is ground. 相似文献
57.
58.
Christian Buchta 《Monatshefte für Mathematik》1986,102(2):91-102
Denoty byp
d+i
(B
d
,d+m) the probability that the convex hull ofd+m points chosen independently and uniformly from ad-dimensional ballB
d
possessesd+i(i=1,...,m) vertices. We prove Mile's conjecture that, given any integerm, p
d+m
(B
d
,d+m)»1 asd». This is obvious form=1 and was shown by Kingman form=2 and by Miles form=3. Further, a related result by Miles is generalized, and several consequences are deduced.Dedicated to Professor E. Halwaka on the occasion of his seventieth 相似文献
59.
The diamagnetic square planar d(8) complexes [meso-arylcorrolato]copper(III) become paramagnetic upon warming, indicative of the equilibrium between the [corrolato]copper(III) and the [corrolato](+)* copper(II) forms of the complex. [meso-Triphenylcorrolato]copper(III) was structurally characterized and found to be saddled. 相似文献
60.
Demetrio De Calle García M. Reichenbächer Klaus Danzer Christian Hurlbeck Christine Bartzsch Karl-Heinz Feller 《Analytical and bioanalytical chemistry》1998,360(7-8):784-787
The extraction of wine aroma compounds was studied by direct-SPME (DI/SPME), headspace-SPME (HS/SPME) and multiple-headspace-extraction-SPME
(MHE/SPME). The aromagrams obtained by HS/SPME-CGC were evaluated with chemometrical methods for the varietal classification
of wines.
Received: 25 July 1997 / Revised: 24 September 1997 / Accepted: 7 October 1997 相似文献