Chalcogens tellurides

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... 

Anodization is facilitated at alkaline pH by the stability of low oxidation state chalcogen species (e.g., Te ) in this range. Thus, intended corrosion of a cadmium electrode in telluride environment may lead to the formation of CdTe ... 

Tertiary phosphine sulfides are generally stable compounds and are not easily oxidised by air, although they can be oxidised by hydrogen peroxide or dilute nitric acid. The analogous tertiary phosphine selenides and tellurides are however, more reactive to oxidation. Similar to the sulfides they can be prepared from the direct reaction of elemental chalcogen with a tertiary phosphine (Equation 1). Tertiary phosphine selenides are also accessible from tertiary phosphines using KSeCN as the selenium source instead of the element itself. 

The final products of oxidation of diarylselenides and tellurides (and sulfides as well) in the presence of nucleophiles are the corresponding chalcogen (IV) compounds. In the presence of water, the selenoxide or telluroxide (or the corresponding dihydroxy selenane or tellurane) is the final product. This still leaves several possible pathways, leveraged from early mechanistic studies done using electrochemical techniques on diaryl sulfides and outlined by Engman (Fig. 32). In these pathways, the initial radical cation can react with a nucleophile present in solution, or the dication resulting from further oxidation or disproportionation can do so. 

The arylmethylselenides ArSeMe and tellurides ArTeMe pose somewhat of a special case in the alkyl aryl compounds, due to the comparatively low reactivity of their radical cations, which do not easily undergo cleavage of the chalcogen-methyl bond, due to the low stability of the resulting methyl radical or cation. 

For comparison within the chalcogens, the oxidation potentials of the Ph-E-Me series 94, 95b, 96b, and 97b, where E = O, S, Se, Te, respectively, were evaluated by pulse radiolysis.Consistent with the analogous diaryl series, the values for this series indicate that the compounds are increasingly easy to oxidize, with telluride 97b most easily oxidized (0.74 V) and ether 94 least easily oxidized (1.62 V), with these values vs. NHE (Table 10). Eor a broader comparison, series of four or five para-substituted arylmethylsulfides, selenides, and tellurides, 95a-e, 96a-e, and 97a-d were prepared and their values determined in the same manner (Table 10). The same trends were observed, with the thioethers least... 

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