Selenides and tellurides

The halides and oxide halides of technetium known thus far [58] are collected in Table 10.4.A. and compared with the known compounds of rhenium. Several halides and oxide halides that are well established for rhenium are still lacking for technetium and are waiting to be discovered. 

Oxidation state and Oxide Fluorides and Oxide Chlorides and Oxide Bromides and Oxide Iodides  

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These two gases can readily be prepared by the action of acids on selenides and tellurides respectively, the reactions being analogous to that for the preparation of hydrogen sulphide. 

These closely resemble the corresponding sulphides. The alkali metal selenides and tellurides are colourless solids, and are powerful reducing agents in aqueous solution, being oxidised by air to the elements selenium and tellurium respeetively (cf. the reducing power of the hydrides). 

All three elements combine readily with most metals and many non-metals to form binary chalcogenides. Indeed, selenides and tellurides are the most common mineral forms of these elements (p. 748). Nonstoichiometry abounds, particularly for compounds with the transition elements (where electronegativity differences are minimal and variable valency is favoured), and many of the chalcogenides can be considered... 

Most selenides and tellurides are decomposed by water or dilute acid to form H2Se or H2Te but the yields, particularly of the latter, are poor. 

Table 22.5 Selenides and tellurides of vanadium, niobium and tantalum...

No other oxide phases below MO2 have been established but a yellow hydroxide , precipitated by alkali from aqueous solutions of chromium(II), spontaneously evolves H2 and forms a chromium(III) species of uncertain composition. The sulfides, selenides and tellurides of this triad are considered on p. 1017. 

Selenides and tellurides are, again, broadly similar to the sulfides in structure and properties. 

The selenides and tellurides of the coinage metals are all metallic and some, such as CuSe2, CuTc2, AgTe. 3 and Au3Tc5 are superconductors at low temperature (as also are CuS and CUS2). 

Selenium and Tellerium Tantalum is attacked by selenium and tellurium vapours at temperatures higher than 80°C. Only slight attack is observed on the metal by liquid selenides and tellurides of ytirum, the rare earths, and uranium at temperatures of 1300 to 2100°C, and tantalum is considered to be a satisfactory material in which to handle these intermetallic compounds. 

Ethyleneimine reacts with (p-tolylsulfonyl)acetylene to give only the (Z)-product 115 via trans addition (equation 91), while primary and secondary aliphatic amines afford ( )-products76. With nonterminal acetylenes such as l-(ethylsulfonyl)-l-propyne, the reactions of ethyleneimine, n-propylamine and f-butylamine give mixtures of ( )- and (Z)-adducts. The double conjugate addition of sodium sulfide, selenide and telluride to bis(l-propynyl)sulfone (116) produces heterocycles (117) as illustrated in equation 9277. 

The Alkaline-Earth Oxides, etc.—The observed and calculated inter-atomic distances for the alkaline-earth oxides, sulfides, selenides and tellurides are given in Table VIII. Except for the magnesium com-... 

The effect of deformation is shown in the sulfide, selenide and telluride of lead. Especially interesting is the decrease in the crystal radius in the series Mn++, Fe++, Co++, Ni++ there must then come an increase when the shell is completed, at Zn++, with the radius 0.74 A. 

It is also shown that theoretically a binary compound should have the sphalerite or wurzite structure instead of the sodium chloride structure if the radius ratio is less than 0.33. The oxide, sulfide, selenide and telluride of beryllium conform to this requirement, and are to be considered as ionic crystals. It is found, however, that such tetrahedral crystals are particularly apt to show deformation, and it is suggested that this is a tendency of the anion to share an electron pair with each cation. 

Generation of a selenoaldehyde, a selenoketone, and telluroaldehydes by [3,3] sig-matropic rearrangement of allyl alkenyl selenides and tellurides [139]... 

Mills, K. C., Thermodynamic Data for Inorganic Sulphides, Selenides and Tellurides, Butterworth, London (1974)... 

Draganjac M, Rauchfuss TB (1985) Transition metal polysulfides Coordination compounds with purely inorganic chelate ligands. Angew Chem Int Ed Engl 24 742-757 DuBois MR (1989) Catalytic applications of transition metal complexes. Chem Rev 89 1-9 Ansari MA, Ibers JA (1990) Soluble selenides and tellurides. Coord Chem Rev 100 223-266... 

Roof LC, Kolis JW (1993) New developments in the coordination chemistry of inorganic selenide and telluride ligands. Chem Rev 93 1037-1080... 

The induced co-deposition concept has been successfully exemplified in the formation of metal selenides and tellurides (sulfur has a different behavior) by a chalcogen ion diffusion-limited process, carried out typically in acidic aqueous solutions of oxochalcogenide species containing quadrivalent selenium or tellurium and metal salts with the metal normally in its highest valence state. This is rather the earliest and most studied method for electrodeposition of compound semiconductors [1]. For MX deposition, a simple (4H-2)e reduction process may be considered to describe the overall reaction at the cathode, as for example in... 

Rare earth sulfides, selenides, and tellurides show semiconducting properties and have potential for application in thermoelectric generation. Thin film chalcogenides of various rare earths have been prepared by multisource evaporator systems [233]. 

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