Modulated Crystal Structure and Electronic Properties of Semiconductor Cu47Si91P144

Crystals of the copper silicon phosphide were synthesized by the iodine gas transport technique. The x‐ray single crystal methods revealed a big superstructure with the lattice parameters a = b = 44.510 and c = 20.772 Å and a basic tetragonal substructure with a = 3.7092 and c = 5.1930 Å. Analysis of the intensities showed that the superstructure has a ¹/₂,¹/₂,¹/₂ tetragonal substructure with a = 22.255 and c = 10.386 Å. This ¹/₂,¹/₂,¹/₂ substructure (Cu₄₇Si₉₁P₁₄₄) and the basic tetragonal structure (Cu_0.71Si_1.29P₂) were solved by the direct methods and refined in the I4m2 space group. The phosphide is a semiconductor with a small energy gap of 0.0269(1) eV. The electrical properties are considered in terms of Anderson localization. The density of states was calculated using the extended Hückel tight binding method.     

Analysis of the convergence of the general coupling operator method for one-configuration-type wave functions

We comment on the convergence of the general coupling operator for all types of one-configuration or multiconfigurational wave functions that still preserve the one-configuration structure for the energy expression. The choice on the best arbitrary real and antisymmetric parameters inherent in the coupling operator methodology is discussed, giving a theoretical reason. Another type of coupling operator is defined, presented, and analyzed. Finally, we give some numerical examples related to the low-lying electronic states of a cluster model for K₂NiF₄ solid. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 368–376, 1998     

Conductivity of Dilute Aqueous Electrolyte Solutions at High Temperatures and Pressures Using a Flow Cell

A flow-through electrical conductance cell was assembled in order to measuremolar conductances of dilute aqueous electrolytes with a high degree of accuracyat high temperatures and pressures. The design of the cell is based on the conceptdeveloped at the University of Delaware and built in 1995, with modificationsthat will allow the cell to operate at much higher temperatures (to 600°C) andpressures (to 300 MPa). At present, the cell has been tested successfully bymeasuring aqueous (10^–4-10^–3 mol-kg^–1) solutions of LiCl, NaCl, and KCl attemperatures 25–410°C and pressures 9.8–33 MPa. The results are in goodagreement with reported values, including those measured with the Delawareflow-through cell. These new results are also complementary to our previousresults, which were measured with a static high-pressure cell. Measurements attemperatures near the critical point of water (374°C, 22.1 MPa) require the useof lower solution concentrations that were unachievable in the past with thestatic cell.     

Comparison of Electrolytic Conductivity Theories: Performance of Classical and New Theories

Conductivity equations, based on the mean spherical approximation (MSA), haverecently been derived. We compare their performance with that of classicalequations at the level of experimental uncertainty using conductivity data forsome typical electrolyte solutions. For symmetrical electrolytes, the pictureisconsistent showing a better performance for the classical equations. The Leeand Wheaton equation also shows advantages at moderate concentrations. Forunsymmetrical electrolytes, the differences between MSA and classical equationsis larger. There is, however, an inherent inconsistency with the equilibriuminformation, which cannot be resolved at present.     

Structural Analysis of the Michael-Michael Ring Closure (MIMIRC) Reaction Products

A representative number of decalin and hydrindane derivatives 2a–l were prepared in 11–91% yield by means of a cascade reaction of cyclohexanone/cyclopentanone enolates and methyl acrylate through a Michael–Michael ring closure (MIMIRC) process. The relative stereochemistry of the four stereogenic centers formed in all products was determined by analyzing the vicinal coupling constants from the ¹H NMR and X-ray crystallography. Such a stereochemical outcome was corroborated by conformational analysis supported by DFT calculations and simulating the ¹H NMR spectra of representative products. All products showed the same relative stereochemistry at C-1 and C-8a, while at C-3 and bridgehead carbon C-4a, configurational changes were observed. The present results provide some insights about the scope and limitations of the triple cascade reaction between cycloalkanone enolates with methyl acrylate. This synthetic protocol is still a simple and very practical alternative to generate decalin and hydrindane derivatives with great structural diversity.     

Der lokale mikrochemische Nachweis der Tonerde

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Literatur

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