Arsenic, crystal structure

Silicon is the most popular material for photovoltaic (PV) power. Another material is gallium arsenide (GaAs), which is a compound semiconductor. GaAs has a crystal structure similar to that of silicon, but it consists of alternating gallium and arsenic atoms. It is well suited for PV applications since it has a high light absorption coefficient and only a thin layer of material is required, which reduces the cost. 

The cyclic arsine (AsMe) reacts with Mn2(CO)jQ at room temperature in daylight to give [Mn2(CO)g(AsMe)5] and at high temperature to give [MnlCOlj-(AsMe) ]2 structures (5) and (6) are proposed in which the metal-metal bond is replaced by bridging arsenic atoms. The crystal structure of [( 0)5-MnAsMc2Cr(CO)5] has been reported. The arsenic atom bridges the two... 

In the latter, the valency angles must be about 100°, so the layers cannot be flat. Their shape is obtained if, in Figure 38, the atoms shown with the clear circles are displaced somewhat below the plane of the paper and the shaded ones similarly, above it. If the layers formed in this way are then arranged on top of one another, the crystal structure of the elements arsenic, antimony and bismuth are obtained in their normal forms in which they have metallic properties. There also exists a modification of phosphorus with a similar structure. In addition, there are other forms of arsenic and antimony, the properties of which correspond to those of yellow phosphorus these forms contain molecules p As4 and Sb4. 

The crystal structure of Compound 4, which was found to possess a centro-symmetric triclinic unit cell containing six tetraphenylarsonium cations, two [Nii2(CO)2iH]3 trianions, and two solvent acetone molecules, also was solved by the combined Patterson-Fourier method, based on the assumption of the dodecanickel core of the trianion being analogous to that of the dianion. Peaks corresponding to all of the nickel and arsenic atoms were first located from successive Fourier syntheses in the unit cell under noncentrosymmetric PI symmetry, after which initial atomic coordinates for the 12 independent nickel and three independent arsenic atoms were obtained by an origin shift to an approximate center of symmetry relating pairs of these peaks to one another. 

Fig. 4. Computer-generated crystal structure models nop row. left to right) Cuprite, zinc-blende, rutile, perovskite. iridymite (second row) Cristobalite. potassium dihydrogen phosphate, diamond, pyrites, arsenic (third rowt Cesium chloride, sodium chloride, wurtzite. copper, niccolite (fourth row) Spinel, graphite, beryllium, carbon dioxide, alpha i uanz. [AT T Bel Laboratories ...

There is a recent review of two-coordinate phosphorus complexes.306 Malisch et a/.307 observed the reversible reaction (86), in which a metal-arsenic(III) double bond is formed, i.e. the M—As a bond is augmented by the arsenic lone pair to form a n bond system (since the cyclopentadienyl coligand is not coplanar with the M=As, the arsenic double bond is isolated). Complex (58) undergoes reactions typical of double bond molecules (Scheme 14). Phosphorus analogues have also been prepared (Scheme 15) the crystal structure of product (c) in Scheme 15 has been solved (59a). The d(W—P) of 2.181 A is shorter than the predicted rf(W=P) of 2.26 A, and the trigonal planar coordination of phosphorus indicates sp2 hybridization.308... 

Ternary compounds have been observed for the R-Si, Ge, Sn, Ga, In, Se, Te-Sb systems. The systems with arsenic and bismuth are characterized by formation of substitutional solid solutions between isotypic binary pnictides. No compounds have been found in the partly investigated ternary La-Al-Sb system at 773 K (Muravjova, 1971). For the Yb-Al-Sb, the formation and crystal structure of the Yb AlSbn have been reported (Fisher et al., 2000). 

J. S. Edmonds, K. A. Francesconi, J. R. Cannon, C. L. Raston, B. W. Skelton, A. H. White, Isolation, crystal structure and synthesis of arsenobetaine, the arsenical constituent of the western rock lobster Panulirus longipes cygnus george, Tetrahedron Lett., 18 (1977), 1543-1546. 

Many studies on the direct reaction of methyl chloride with silicon-copper contact mass and other metal promoters added to the silicon-copper contact mass have focused on the reaction mechanisms.7,8 The reaction rate and the selectivity for dimethyldichlorosilane in this direct synthesis are influenced by metal additives, known as promoters, in low concentration. Aluminum, antimony, arsenic, bismuth, mercury, phosphorus, phosphine compounds34 and their metal complexes,35,36 Zinc,37 39 tin38-40 etc. are known to have beneficial effects as promoters for dimethyldichlorosilane formation.7,8 Promoters are not themselves good catalysts for the direct reaction at temperatures < 350 °C,6,8 but require the presence of copper to be effective. When zinc metal or zinc compounds (0.03-0.75 wt%) were added to silicon-copper contact mass, the reaction rate was potentiated and the selectivity of dimethyldichlorosilane was enhanced further.34 These materials are described as structural promoters because they alter the surface enrichment of silicon, increase the electron density of the surface of the catalyst modify the crystal structure of the copper-silicon solid phase, and affect the absorption of methyl chloride on the catalyst surface and the activation energy for the formation of dimethyldichlorosilane.38,39 Cadmium is also a structural promoter for this reaction, but cadmium presents serious toxicity problems in industrial use on a large scale.41,42 Other metals such as arsenic, mercury, etc. are also restricted because of such toxicity problems. In the direct reaction of methyl chloride, tin in... 

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