Polyselenides metal

Poly(8-quinolinol) electrode coatings, 19 Polysaccharides metal complexes geochemistry, 868 Polyselenides metal complexes geochemistry, 854 Polytyramines electrode modification, 23 Polyvinylferrocene electrode coatings, 19 attachment, 19 Poly(N-vinylimidazole) metal complexes color photography, 109 Poly(4-vinylpyridine) electrode coatings, 17 redox centres, 17 electrodes, 16 Porins... 

Bina Selenides. Most biaary selenides are formed by beating selenium ia the presence of the element, reduction of selenites or selenates with carbon or hydrogen, and double decomposition of heavy-metal salts ia aqueous solution or suspension with a soluble selenide salt, eg, Na2Se or (NH 2S [66455-76-3]. Atmospheric oxygen oxidizes the selenides more rapidly than the corresponding sulfides and more slowly than the teUurides. Selenides of the alkah, alkaline-earth metals, and lanthanum elements are water soluble and readily hydrolyzed. Heavy-metal selenides are iasoluble ia water. Polyselenides form when selenium reacts with alkah metals dissolved ia hquid ammonia. Metal (M) hydrogen selenides of the M HSe type are known. Some heavy-metal selenides show important and useful electric, photoelectric, photo-optical, and semiconductor properties. Ferroselenium and nickel selenide are made by sintering a mixture of selenium and metal powder. 

Important results and a detailed insight into aqueous chemical deposition processes have been reported and discussed elsewhere for CdSe [248, 249] and ZnS [250, 251] target products. We should note also the work of Davies et al. [252] who described an alternative method for the chemical growth of metal sulfides and selenides on the basis of polysulfide or polyselenide solutions (containing hexa- and tetra-chalcogen anions) formed by the dissolution of sulfur or selenium in hydrazine monohydrate. ... 

Dhingra, S. Kanatzidis, M. G. 1990. The use of soluble metal-polyselenide complexes as precursors to binary and ternary solid metal selenides. Mater. Res. Soc. Symp. Proc. 180 825-830. 

Selenium is soluble in sulphuric acid, forming a green solution which, in the case of the metallic form, probably contains a compound of composition S03Se (p. 338), and in the case of the red amorphous variety, a polymeric form of this compound.8 The presence of selenium does not affect the electrical conductivity of sulphuric aeicl. Dilute aqueous potassium hydroxide dissolves the red variety, producing a solution which probably contains polyselenides in the presence of sodium hydrosulphite, however, only sodium selenide, Na2Se, is obtained.9... 

The ease with which selenium combines with many other elements to form binary compounds has already been mentioned (p. 299). Only one compound with hydrogen is known, but a series of polyselenides of the alkali metals corresponding to the polysulphides has been obtained. Selenium forms a hexafluoride, SeFG, but no other hexalialide has been isolated. The tetrahalides arc the most stable, and mixed chloro-bromides of quadrivalent selenium, SeCl Br, are known. Selenium monochloride, SeaCla, and selenium monobromide, Se2Br2, also exist as comparatively stable liquids at ordinary temperatures. No compound of selenium and iodine is known. Selenium oxychloride, SeOCl2, and the oxybromide, SeOBr2, are extremely reactive and useful compounds. 

The selenides of the alkali metals are white when pure, but generally appear pink owing to the presence of free selenium or of polyselenides, as also do the alkali hydroselenides moreover they readily oxidise in air, with separation of selenium. The selenides of the alkaline earth metals are described as pink, but it is questionable whether they have yet been obtained in a pure condition. 

The chemistry of polyselenides, polytellurides, and their metal complexes is very well established. Typical structures of polyselenide dianions are shown in Fig. 16.8.5. In these species, the Se-Se bond distances vary from 227 to 236 pm, and the bond angles from 103° to 110°. The tethered monocyclic structure of Se - in the complex Sr(15-C5)2(Se9) has a three-connected Se atom forming two long and one normal Se-Se bonds at 295, 247, and 231 pm (anticlockwise in Fig. 16.8.5, with the longest bond represented by a broken line). The other Se-Se bonds are in the range 227-39 pm. 

The reaction of uranium metal with polyselenides in molten potassium polyselenide generates an interesting molecular diselenide complex K4[U(r/ -Se2)4], containing a discrete U( 7 -Se2)4 anion. 

RAY/D1C] Raymond, C. C., Dick, D. L., Dorhout, P. K., Speciation of main-group metal ions by electrospray mass spectrometry. 1. Investigation of aqueous polyselenide species and effects of cations and pH, Inorg. Chem., 36, (1997), 2678-2681. Cited on page 154. 

Chapter 15 Metal sulfides, polysulfides, polyselenides and polytellurides 447... 

Although Se and Te analogues of polysulfanes do not extend beyond the poorly characterized H2Se2 and H2Te2, the chemistries of polyselenides, polytellurides and their metal complexes are well established. Equations 15.43-15.46 illustrate preparations of salts of [Se ] and [Te ] see Section 10.8 for details of crown ethers and cryptands. 

Discrete polyselenide chains Se without significant secondary intra- or inter-molecular Se- Se contacts have been structurally characterized for n = 2-8. Crystal structures are known in addition to K5Sc3 for the following binary alkali metal selenides A2Sen in the range n = 2-5 A2Sc2 for A = Na, K,... 

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