Chalcogens Sulfur Tellurium

The group of the chalcogens sulfur, selenium and tellurium is a typical triad of the more electronegative nonmetals with relatively high-ionization energies, relatively strong element-element bonds and a clear tendency to form mono-and polyatomic anions (Table 1). 

Reaction of germylenes with elemental chalcogens (sulfur, selenium, tellurium) also allowed the synthesis of stable >Ge = E species. This was first exemplified by the isolation of terminal chalcogenido complexes of germanium 170152 and 171-173153 (Scheme 34). Stabilization in these cases is achieved by intramolecular complexation of the metal atom by Lewis bases. 

V. V. Sobolev and A. M. Shirokov, Electronic Structure of Chalcogens. Sulfur, Selenium, and Tellurium, Nauka, Moscow, 1988. 

Pentacarbonyliron(O) is obtained by carbonylation of anhydrous FeE under drastic conditions (200 °C, 200 atm of CO pressure) in the presence of copper as halogen acceptor. This is consistent with the observation that iodo-carbonyls of group 11 metals (Cu, Ag, Au) are unstable with respect to the corresponding metal iodides, and no contamination from other carbonyl products can occur from the use of copper. The yields of Fe(CO)s are essentially quantitative considerably lower yields are obtained with FeCls (1%) or FeBrs (20%). Pentacarbonyliron(O) can also be obtained from finely divided iron at 200 °C under pressure (200 atm) of CO, especially in the presence of chalcogens (sulfur or selenium) as promoters. In the presence of sulfur (0.3at.%), an excellent yield of Fe(CO)s (94%) is obtained selenium (0.3at.% 93% yield) and tellurium (1 at.% 89% yield) are equally good under comparable conditions. Probably iron-carbonyl chalcogenides are formed as intermediates. Some compounds of this type have been reported by independent syntheses and have also been structurally characterized. 

The stabihty of organic chalcogen compounds decreases mosdy ia the order sulfur > selenium > tellurium. 

The reaction of Me3SiNSNSiMc3 with TeCU is an especially fruitful source of chalcogen-nitrogen halides that contain both sulfur and tellurium. The initial product of this reaction is the bicyclic compound 8.17, which is obtained when the reaction is carried out in a 1 2 molar... 

The acyclic imidoselenium(II) dihalides ClSe[N( Bu)Se]nCl (8.23, n =1 8.24, n = 2) are obtained from the reaction SeCla with tert-butylamine in a 2 3 molar ratio in THF. There are no sulfur or tellurium analogues of this class of chalcogen-nitrogen halide. 

In general, it was found that this process is strongly endothermic for sulfur diimides, approximately thermoneutral for selenium diimides and strongly exothermic for tellurium diimides, consistent with experimental observations. These differences can be attributed to the expected trend to lower r-bond energies for chalcogen-nitrogen (np-2p) r-bonds along the series S (n = 3), Se (n = 4) and Te (n = 5). 

The heavier chalcogens are more prone towards secondary interactions than sulfur. In particular, the chemistry of tellurium has numerous examples of intramolecular coordination in derivatives such as diazenes, Schiff bases, pyridines, amines, and carbonylic compounds. The oxidation state of the chalcogen is also influential sulfur(IV) centres engender stronger interactions than sulfur(II). For example, the thiazocine derivative 15.9 displays a S N distance that is markedly longer than that in the corresponding sulfoxide 15.10 (2.97 A V5. 2.75-2.83 A, respectively). ... 

The chalcogenides are binary compounds of a chalcogen (i.e., the elements of Group Ilb zinc, cadmium, mercury) with a less electropositive element, such as those of Group VIb (oxygen, sulfur, selenium, and tellurium). This section covers the sulfides, selenides, andtellurides. Oxides are reviewed above in Ch. 11. Most of the chalcogenides have useful optical characteristics and their applications are usually found in optics. 

Sheldrick WS (2007) Polychalcogenides. In DevrUanova FA (ed.), Handbook of chalcogen chemistry New perspectives in sulfur, selenium and tellurium, Royal society of Chemistry Cambridge, UK... 

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... 

The oxidation of the phosphasilenes 12a and 15a with elemental sulfur and tellurium led the corresponding chalcogen heterocycles 23 (Eqs. 7,... 

Some of the fundamental properties of sulfur, selenium and tellurium differ significantly from those of oxygen, giving rise to disparities between the structures and properties of heavier chalcogen-nitrogen molecules and ions compared to those of their N-O counterparts. The major contributors to these differences include the following ... 

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