The Chalcogens

As a matter of fact, this book is concerned with sulfur, selenium, and tellurium as components of compound or solid solution systems in which metallic or semimetal-lic elements, whatsoever, participate as well. In particular, it is focused on the electrochemistry of the inorganic compounds of sulfur, selenium, and tellurium with metals and semimetals, which collectively may be termed as metal chalcogenide (MCh) systems. 

Bouroushian, Electrochemistry of Metal Chalcogenides, Monographs in Electrochemistry, DOI 10.1007/978-3-642-03967-6 l, 

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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]... 

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

The electrochemistry of S-N and Se-N heterocycles has been reviewed comprehensively. The emphasis is on the information that electrochemical studies provide about the redox properties of potential neutral conductors. To be useful as a molecular conductor the 4-1, 0, and -1 redox states should be accessible and the neutral radical should lie close to the centre of the redox spectrum. The chalcogen-nitrogen heterocycles that have been studied in most detail from this viewpoint... 

The third class of compounds to be discussed in this chapter are those in which an RE group (E = S, Se, Te) is attached to a nitrogen centre. This category includes amines of the type (REfsN and the related radicals [(RE)2N] , as well as organochalcogen(ir) azides, REN3, and nitrenes REN (E = S, Se). Covalent azides of the type RTe(N3)3 and R2Te(N3)2, in which the chalcogen is in the +4 oxidation state, have also been characterized. 

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 involvement of a chalcogen atom in an intramolecular interaction may influence the reactivity of the chalcogen centre as a result of steric or electronic effects. This feature may lead to unique reaction patterns. Eor example, the sulfur(II) centre involved in an intramolecular contact... 

Carbon forms binary compounds with most elements those with metals are considered in this section whilst those with H, the halogens, O, and the chalcogens are discussed in subsequent sections. Alkali metal fullerides and encapsulated (endohedral) metallafullerenes have already been considered (pp. 285, 288 respectively) and met-allacarbohedrenes (metcars) will be dealt with later in this section (p. 300). Silicon carbide is discussed on p. 334. General methods of preparation of metal carbides are ... 

Molten Pb reacts with the chalcogens to give PbS, PbSe and PbTe. 

None of the three elements is particularly abundant in the earth s crust though several minerals contain them as major constituents. As can be seen from Table 13.1, arsenic occurs about halfway down the elements in order of abundance, grouped with several others near 2 ppm. Antimony has only one-tenth of this abundance and Bi, down by a further factor of 20 or more, is about as unabundant as several of the commoner platinum metals and gold. In common with all the post-transition-element metals. As, Sb and Bi are chalcophiles, i.e. they occur in association with the chalcogens S, Se and Te rather than as oxides and silicates. 

The mineral laurite is the mixed sulphide (Ru,Os)S2 this and RuS2 and OsS2 have the pyrite structure as does RuQ2 (Q = Se, Te). These can be made from the reaction of the chalcogen with the metals, while RuCl3 will also react with Se and Te. 

Fig. 1. Chalcogenide halides in ternary systems having the components the Group IB elements Cu, Ag, and Au, the chalcogens S, Se, and Te, and the halogens Cl, Br, and I, They are indicated as M , Y, and X ", respectively. (Redrawn from A. Rabenau, H. Rau, and G. Rosenstein, J. Less-Common Metals 21, 395 (1970), Fig. 4, p. 401.)...

The compounds AlYX are best prepared by direct reaction between the respective aluminum halide and chalcogenide in a sealed ampoule at 350°C. The reaction is complete after 2 weeks. In the case of the iodides, a mixture of A1 and I2 (molar ratio 3 10) is used instead of AII3. Other preparative methods, such as the reaction of an aluminum halide with Zn or Cd chalcogenide, or with the chalcogen itself, are applicable to the bromide and chloride only, and give poor yields (15-20%) (158, 159, 266, 327, 328). 

TI4SCI4 and T SeCh melt at 440 and 442°C, respectively. They can be distilled between 650 and 700°C without decomposition. They are insoluble in H2O and organic solvents, but soluble in aqueous alkaline solutions. With cone, acids, decomposition takes place. The electric conductivity has been determined to be 1.4-10 and 2.1-10 fl cm for TI4SCI4 and TUSeCU, respectively. The probable structural formula is Tl3(TlCl4Y). The compounds thus, presumably, consist of Tli,4Cl4,4Y2/8 octahedra that are interconnected by the chalcogen atoms to linear chains (321). 

The chalcogen-capped clusters M M2Co(/(3-S)(CO)s()/ -CsH5) (M M2 = MoEc, MoRu, WFe) and MoFeCo(/r ,-Se)(CO)H()) -CsH3) underw ent a one-electron, quasi-reversible reduction. Addition of an electron proceeded more readily for the clusters w ith the lighter metals and for the selenium capped cluster relative to its sulfur analogue. 

Fig. 14.1 Representations of main group chalcogen polyhedra. In each figure, the main group element (Si, Ge) is darker, and the chalcogen (S, Se,Te) is shown lighter, (a)...

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