Chalcogen

Radicals analogous to the above containing other chalcogens in place of oxygen are named by adding the prefixes thio-, seleno-, and so on for example, PS, thiophosphoryl CS, thiocarbonyl. 

Replacement of Oxygen by Other Chalcogens. Acids derived from oxoacids by replacement of oxygen by sulfur are called thioacids, and the number of replacements are given by prefixes di-, tri-, and so on. The affixes seleno- and telluro- are used analogously. 

There is another class of amorphous semiconductors based on chalcogens which predate the developments that have occurred in i -Si. Because their use has been limited, eg, to switching types of devices and optical memories, this discussion is restricted to the optoelectronic properties of i -Si-based alloys and their role in some appHcations. 

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

Dibismuthines are very sensitive to oxidation. Thus tetramethyldibismuthine fumes ia air, and tetraphenyldibismuthine ia toluene solution rapidly absorbs oxygen. Under controlled conditions, dibismuthines react with chalcogens resulting ia cleavage of the bismuth—bismuth bond and iasertion of a chalcogen atom (105,138,140—142) ... 

Fig. 8. Sensitizing dyes of the cyanine class. K. = N — alkyl or chalcogens (O, S, Se, Te) R = chloro, phenyl, or additional benzene ring R = methyl, ethyl, or hydrogen n = 0, 1, 2 and RPRIME, R " = alkyl or sulfoalkyl. Solubihty in methanol for a carbocyanine dye n = 1 X = S R = Cl R = ethyl. Cationic dye (R" = R " = ethyl anion = bromide) 9.5 mmol/T. neutral dye (R" = ethyl R " = sulfopropyl) 3.6 mmol/L anionic dye (R" = R = sulfopropyl ...

By long tradition, a group of cationic pyran derivatives have trivial names, i.e. (186)-(189), which are retained by lUPAC. These names may be modified by the prefixes thio-, seleno-and telluro- for their chalcogen analogs. 

The chalcogene heterocycles have been used as stable precursors for sulfur-said selenium-cantaining hetero-l,3-dienes in cycloaddition reactions 3//-l,2,4-Thiaselenazoles are a convenient source of 4,4-bis(trifluoromethyl)-l-thia-3-aza-buta-1,3-dienes, and 3//-diselenazoles are a convenient source of 4,4-bis(trifluoromethyl)-l-selena-3-azabuta-l,3-dienes as well as bis(tnfluoro-methyl)-substrtuted nitrile ylides [137]... 

Cyclic chalcogen imides in which sulfur is in the formal -f2 oxidation state (or lower) can, in the case of sulfur, act as a source of binary S-N... 

Polymer and chain formation is another property of chalcogen-nitrogen compounds that distinguishes them from their oxygen analogues. In addition to the unique, superconducting poly(sulfur nitride) (SN) (1.24) (Section 14.2), a variety of poly(thiazyl) chains such as RS5N4R (1.25) (Section 14.3) have been characterized. Interest in these chains stems from their possible use as models for the behaviour of (SN) and as components in molecular materials, e.g., as molecular wires. 

Chalcogen-Nitrogen Compounds with the Chalcogen in Higher Oxidation States... 

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,... 

A. Haas, Some Recent Developments in Chalcogen Heterocyclic Chemistry, Adv. Heterocycl. Chem., 71, 115 (1998). 

Reactions of ionic or covalent azides with chalcogen halides or, in the case of sulfur, with the elemental chalcogen provide an alternative route to certain chalcogen-nitrogen compounds. Eor example, the reaction of sodium azide with cyclo-Sa in hexamethylphosphoric triamide is a more convenient synthesis of S7NH than the S2CI2 reaction (Section 6.2.1). Moreover, the azide route can be used for the preparation of 50% N-enriched S7NH. 

Chalcogen-nitrogen cations can be generated by the reactions of homopolyatomic chalcogen cations with azides. For example, the... 

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