Selenium structures

A schematic sketch of the selenium. structure showing how the zig-zag chain can be coiled up along a [111] direction in a simple cubic lattice. Every third atom along the coil is translationally equivalent one such set is shaded. Other chains may be added such that the isolated shaded atoms shown are translationally equivalent to the shaded atoms in the chain and there is an atom site at every cube corner. The structure can then be distorted to reduce intrachain atom distances, increase interchain distances, and increase the bond angles to 105°. 

Within the molecular sheets the interbond angles are almost exactly 90°, suggesting that simple pz orbitals are involved in the covalent bonding. The forces between the sheets are primarily van der Waals bonds, but, as in the selenium structure, there is no doubt that these forces also have an appreciable component of metallic character which increases with increasing atomic number, as is shown by the progressive... 

Bonds to Sulphur or Selenium.—Structures (114) and (115), respectively, are assigned on the basis of i.r. data, etc.y to the sulphides P4S9 and P4S4 obtained... 

The general formula RuSe describes rathenium particles that are modified by a small amount of selenium the optimum activity is achieved for x 0.1. As obtained from anomalous small angle X-ray scattering (ASAXS) measurements, ruthenium forms almost spherical nanoparticles from which the selenium content is deposited onto the surface. The typical size of the rathenium particles is around 2.5 mn selenium forms small clusters on the surface with a diameter <0.6 nm. A mixing of the two components has not been observed. From extended X-ray absorption fine structure (EXAFS) analysis an oxygen-free selenium structure and oxygen-containing species on the uncovered rathenium surface... 

Diselenium dichloride acts as a solvent for selenium. Similarly disulphur dichloride is a solvent for sulphur and also many other covalent compounds, such as iodine. S Clj attacks rubber in such a way that sulphur atoms are introduced into the polymer chains of the rubber, so hardening it. This product is known as vulcanised rubber. The structure of these dichlorides is given below ... 

Selenium exists in several allotropic forms. Three are generally recognized, but as many as that have been claimed. Selenium can be prepared with either an amorphous or crystalline structure. The color of amorphous selenium is either red, in powder form, or black, in vitreous form. Crystalline monoclinic selenium is a deep red crystalline hexagonal selenium, the most stable variety, is a metallic gray. 

The first compounds with a Aj selenazoline structure were mentioned in the literature in 1892 by Michels (55). He prepared 2-methyl-A -selenazoline in the course of his investigations into sulfur and selenium... 

Fig. 4. Grain structure of lead—2 wt % antimony alloy battery grid at a magnification of 50x (a) no nucleants (b) containing 0.025 wt % selenium as a grain...

On the assumption that the two alkaloids may have a similar structure and, with that reservation, applying the result of the selenium dehydrogenation experiment to the case of solanocapsine, the authors suggest that the annexed formula (p. 670) aeeounts for all the reae ions of this alkaloid so far observed. 

The selenium-dehydrogenation products of fsorubijervine have not yet been fully examined, but the two structurally significant products, 5-methyl-2-ethylpyridine and a hydrocarbon, m.p. 135-6°, yielding... 

G. Faivre, J. L. Gardissat. Viscoelastic properties and molecular structure of amorphous selenium. Macromolecules 79 1988-1996, 1986. 

The accessibility of the +4 and +6 oxidation states for sulfur and, to a lesser extent, selenium gives rise to both acyclic and cyclic molecules that have no parallels in N-O chemistry. Thus there is an extensive chemistry of chalcogen diimides RN=E=NR (E = S, Se, Te) (Section 10.4). In the case of Te these unsaturated molecules form dimeric structures reflecting the increasing reluctance for the heavier chalcogens to form multiple bonds to nitrogen. The acyclic molecule N=Sp3,... 

J. D. Woollins, The Preparation and Structure of Metalla-sulfur/selenium Nitr ogen Complexes and Cages, in R. Steudel (ed.) The Chemistry of Inorganic Heterocycles, Elsevier, pp. 349-372 (1992). 

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