Tellurium-selenium cations

Dilution with water reverses the reaction, and heating the solution liberates sulfur dioxide. Upon being added to a solution of tellurides, tellurium forms colored polytellurides. Unlike selenium, tellurium is not soluble in aqueous sodium sulfite. This difference offers a method of separating the two elements. Like selenium, tellurium is soluble in hot alkaline solutions except for ammonium hydroxide solutions. Cooling reverses the reaction. Because tellurium forms solutions of anions, Te2-, and cations, Te4+, tellurium films can be deposited on inert electrodes of either sign. 

The species, SeJ and TeJ, appear to be square-planar like whose similarity is supported by theoretical calculations that treat all of them as 6-ir electron systems.The yellow selenium cation is obtained by treating elemental selenium with fluorosulfuric acid, fuming sulfuric acid, sulfur trioxide, disulfuric acid, or antimony pentafluoride. The red tellurium cation is obtained simi-larly. = ... 

A number of metal 1,2-dithiolenes, mainly corresponding to 1,3-dithioles of Class 0 (Table l),and selenium-, tellurium-, etc- anaIogs,have been described in refs [10]-[12] and refs therein. Recent work has been described in refs [48], [52], [54]. In this section we describe methods of preparation and properties of cation-rich salts of some metal 1,2-dithiolenes and selenium analogs, having ligands with additional heteroatoms (S,Se,N) to an additional ring or chain. These are compounds of the following formulas, ( QII)-(XXII),... 

Like the halogen cations, the sulfur, selenium, and tellurium cations are highly electrophilic and undergo disproportionation in media with any appreciable basic properties, although, as would be anticipated, the ease of disproportionation increases in series tellurium < selenium < sulfur. 

Hearley, A.K., Johnson, B.F.G., Mclndoe, J.S., Tuck, D.G. (2002) Mass spectrometric identification of singly-charged anionic and cationic sulfur, selenium, tellurium and phosphorus species produced by laser ablation. Inorganica Chimica Acta, 334,105-112. 

Although tellurium resembles sulfur and selenium chemically, it is more basic, more metallic, and more strongly amphoteric. Its behavior as an anion or a cation depends on the medium, eg ... 

The selenium analogue [PhCNSeSeN] and cyano-functionalized diselenadiazolyl radicals adopt cofacial dimeric structures, e.g., 11.4 (E = Se), with unequal Se Se interactions of ca. 3.15 and 3.35 A. In the latter case the radical dimers are linked together by electrostatic CN Se contacts.Tellurium analogues of dithiadiazolyl radicals (or the corresponding cations) are unknown, but calculations predict that the radical dimers, e.g., 11.4 (E = Te), will be more strongly associated than the sulfur or selenium analogues. ... 

In the anion electrochemical series, sulfur, being the less noble element compared to its heavier congeners, occupies an intermediate position between iodine and selenium [(+)F, Cl, Br, I, S, Se, Te(-)]. Selenium, regarded as a metalloid, is a relatively noble element. Tellurium is rather an amphoteric element it can enter into solution in the form of both cations and anions. Regarded as a metal, i.e., with respect to its cations, tellurium occupies a position between copper and mercury. Regarded as a metalloid, i.e., with respect to its anions, it is located on the extreme right of the above series. 

Numerous Zind anions are formed by selenium and tellurium, with some of the more prominent species being Se 2 (where n 2, 4, 5, 6, 7, 9, or 11). The species with n = 11 contains two rings that have five and six members that are joined by a selenium atom. Those with smaller numbers of selenium atoms generally consist of zigzag chains. Tellurium forms an extensive series of polyanions that are present in such species as NaTe (n = 1 to 4). One tellurium anion contains the Hg4Te124 ion, but other species such as [( lg2Tes) 2 are also known, such as the Te122 anion that is present in some cases where the cation is a +1 metal. 

Cations that contain sulfur, selenium, and tellurium have also been studied for many years. One of the most common ions of this type is S42+, which has the following square planar structure. This is also the structure of Se42+ andTe42+, which have the dimensions shown. 

Table 2 Characterized examples of binary sulfur, selenium, and tellurium halogen cations...

Although it had been known since the early 19th century that elemental sulfur, selenium and tellurium dissolve in oleum to afford intensively colored solutions, it was not until the 1960s that the structures of the responsible homopolyatomic cations began to be elucidated in detail. 

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