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991.
J. Medved Vladimír Streko Jana Kubová Jozefa Polakoviová 《Fresenius' Journal of Analytical Chemistry》1998,360(2):219-224
Nine decomposition procedures for soil samples, such as via acid mixtures and fusion in open systems and microwave and autoclave
dissolution (in closed systems under elevated temperature and pressure) were assessed using certified soil reference materials.
The determination of various elements in solutions was performed by FAAS and ICP-OES and the results were compared with certified
values and with direct current arc OES analysis.
Received: 3 March 1997 / Revised: 30 May 1997 / Accepted: 3 June 1997 相似文献
992.
A nickel catalyst was nodeled with ligand L^2,[NH=CH-CH=CH-0]^-,which should have potential use as a syndiotactic plyolefin catalyst,and the reaction mechanism was studied by theoretical calculations using the density functinal method at the B3LYP/LANL2MB level.The mechanism involves the formation of the intermediate [NiL^2Me]^ ,in which the metal occupies a T-shaped geometry.This intermediate has two possible structures with the methyl group trans either to the oxygen or to the nitrogen atom of L^2.The results show that both structures can lead to the desired product via similar reaction paths,A and B.Thus,the polymerization could be considered as taking place either with the alkyl group occupying the position trans to the Ni-0 or trans to the Ni-N bond in the catalyst.The polymerization process thus favors the catalysis of syndiotactic polyolefins.The syndiotactic synthesis effects could also be enhanced by varations in the ligand substituents.From energy considerations,we can conclude that it is more favorable for the methyl ttrans-O position to form a complex than to occupy the trans-N position.From bond length considerations,it is also more favoured for ethene to occupy the trans-O position than to occupy the trans-N position. 相似文献
993.
The novel complex [K(18-C-6)]2[Cd(mnt)2][18-C-6-18-crown-6,nmt=1,2-dicyanoethene-1,2-dithiolate,C2S2-(CN)2^2-] was synthesized and characterized by elemental analysis,IR spectrum and X-ray diffraction analysis.The complex displays two-dimensional network structure of [K(18-C-6)] complex segments and [Cd(nmt)2] complex segment bridged by S-K-S,S-K-N and N-K-N interactions between adjacent[K(18-C-6)] and [Cd(mnt)2]units. 相似文献
994.
García ME Riera V Ruiz MA Sáez D Vaissermann J Jeffery JC 《Journal of the American Chemical Society》2002,124(48):14304-14305
Protonation of [Mo2Cp2(mu-H)(mu-PHR*)(CO)4] (Cp = eta5-C5H5, R* = 2,4,6-C6H2tBu3) with HBF4.OEt2 gives the hydridophosphinidene complex [Mo2Cp2(mu-H)(mu-PR*)(CO)4]BF4, which is easily deprotonated with H2O to give the known phosphinidene complex [Mo2Cp2(mu-PR*)(CO)4] in 95% yield. Reaction of the latter with I2 gives the unsaturated phosphinidene complex [Mo2Cp2I2(mu-PR*)(CO)2], which exhibits an intermetallic distance of 2.960(2) A. Irradiation of solutions of [Mo2Cp2(mu-PR*)(CO)4] with UV light gives a mixture of the triply bonded [Mo2Cp2(mu-PR*)(mu-CO)2] and the hydridophosphido derivative [Mo2Cp2(mu-H){mu-P(CH2CMe2)C6H2tBu2}(CO)4] as major species. The latter complex results from an intramolecular C-H bond cleavage from a tBu group and has been characterized by spectroscopy and an X-ray study. Irradiation in the presence of HCC(p-tol) results in the insertion of the alkyne into the Mo-P bond to give [Mo2Cp2{mu-eta1:eta2,kappa-C(p-tol)CHPR*}(CO)4] structurally characterized through an X-ray study. 相似文献
995.
996.
Principles of two computer programs useful for the evaluation of heterogeneous kinetics are described.The first program ALANTA allows to obtain the non-isothermal kinetic curve from the shape of general DTA peak using the DTA-equation derived elsewhere1.The second program SQUEST determines the kinetic mechanism which is the most appropriate to a given non-isothermal kinetic curve and evaluates the corresponding kinetic parameters. The program decides between 19 kinetic models and uses both integral and differential methods of evaluation. 相似文献
997.
M.P. Sánchez-Sánchez J.M. Salas-Peregrín M.A. Romero-Molina A. Mata-Arjona 《Thermochimica Acta》1985,88(2):355-361
The thermodynamic protonation constants of 4-amino-1,6-dihydro-2-methylthio-5-nitroso-6-oxo-pyrimidine (MTH), 4-amino-5-nitroso-6-oxo-1,2,3,6,-tetrahydro-2-thiopyrimidine (TANH) and 2-thioxanthine (TXH) in aqueous media at 25, 30, 40 and 50 ± 0.1°C, have been determined potentiometrically by Bjerrum and Robinson's methods. The ionic strength was maintained constant by using 0.1 M NaNO3 as the supporting electrolyte.The stability constants and thermodynamic functions for Zn(II) and Cd(II) complexes of MTH and TXH, at different ionic strengths and temperatures, have been calculated. 相似文献
998.
Zinc phosphites ZnPHO3·2.5 H2O, Zn2H2P3H3O9·H2O, Zn3H4P5H5O15·1.5 H2O, ZnH2H2P2H2O6 have been studied at higher temperatures and by X-rays and molecular spectroscopy. Hydrates ZnPHO3·2.5 H2O and Zn2H2P3H3O9·H2O, when heated, yield an anhydrous salt. Thermal decomposition of dihydrogen triorthophosphite and tetrahydrogen pentaorthophosphite leads, before oxidation of the anion, to a mixture of zinc phosphite ZnPHO3 and dihydrogen diorthophosphite ZnH2P2H2O6 and then after loss of water of constitution dihydrogen diorthophosphite converts to zinc diphosphite ZnP2H2O5. The results of the thermal decomposition study were confirmed by X-ray investigation. Anhydrous zinc dihydrogen triorthophosphite Zn2H2P3H3O9 and zinc diphosphite ZnP2H2O5 were hitherto unknown. Infrared spectra confirmed the existence of hydrogen bonding in all the phosphites studied and in the case of zinc phosphite ZnPHO3·2.5 H2O exhibited a symmetry decrease of the anion PHO3
2– from the point group C3v to Cs. In the crystal lattice of ZnPHO3·2.5 H2O hydrogen bonding by water molecules participates, with polyorthophosphites hydrogen bonding shares in the production of anions and in the case of their hydrates there is in addition hydrogen bonding by water molecules.
Mit 3 Abbildungen 相似文献
Mit 3 Abbildungen 相似文献
999.
José Fernández Bertrán Boris La Serna Klaus Doerffel Klaus Dathe Gunther Kabish 《Journal of Molecular Structure》1982
The Fermi doublet V2?V3 + V4 of CH3CN in basic, inert and acidic solvents has been studied by IR and Raman spectroscopy. The values of W, the Fermi coupling coefficient, obtained from IR spectra varies with the nature of the solvent while W evaluated from Raman data remains constant at 12.5 ± 0.5 cm?1. The similar effects of Bronsted and Lewis acids on the band frequencies and intensities is evidence that the CN group complexes with acids via the N atom “n” electron pair and not the π bond. 相似文献
1000.
The rapid gas chromatographic detection and determination of ethylene glycol in biological fluids is described. Phenylboronic acid in acetone was used for the esterification of glycol. The phenylboronates of ethylene glycol and 1,2-propylene glycol are not separated on a packed column of medium polarity (OV-17), but they can be separated on a non-polar column (OV-101). In both instances, 1,3-propylene glycol can be used as an internal standard. The method requires only 100 microliters of serum or urine and is suitable for trace analysis in an emergency toxicological laboratory. The utility of the method is demonstrated on two cases of human intoxication with ethylene glycol. 相似文献