Tellurium-sulfur cations

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

Furukawa, N. Creation of organo-sulfur, -selenium- and - tellurium multi-cation species. Phosphorus, Sulfur and Silicon and the Related Elements 199B, 136,137 138, 43-58. 

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. 

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. 

Thus, sulfur is the element richest in allotropes,1 while tellurium holds the record for the number of positively charged polyatomic cations. Moreover, tellurium (and to a lesser extent Se) is at the border between a nonmetal and a metal thus, solid grey Se and Te are semiconductors and especially... 

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. 

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. 

Although there are similarities between the chemistry of the chalcogenide elements, the properties of selenium and tellurium clearly lie between those of non-metallic sulfur and metallic polonium. The enhancement in metallic character as the group is descended is illustrated in the emergence of cationic properties by polonium, and marginally by tellurium, which are reflected in the ionic lattices of polonium(IV) oxide and tellurium(IV) oxide and the formation of salts with strong acids. 

Trialkyl cations of oxygen, sulfur, and selenenium (and less commonly tellurium) are onium ions by virtue of their having one extra valence, although these three-coordinate ions invite comparison with carbenium ions. These ions (e.g., 28, 29, and 30) are not planar (as opposed to the analogous carbenium ions), but rather are pyramidal. These species have a well-characterized solution acid chemistry concentrated sulfuric acid is required for observation of the trimethyloxonium cation, but the sulfonium and selenonium ions require less strongly acidic solutions. 

Polyheteroatom Cations. So far, only studies on homopolyatomic cations of oxygen, sulfur, selenium, and tellurium have been discussed. Most of them were of the type X,21. There is a new class of polyatomic cations that comprise two or more heteroatoms. 

The reactions of the dibenzo derivative of the tellurapyrylium cation, 10-telluroniaanthracene, were studied in considerable detail. In general, the reactions of tellurapyrylium salts are similar to those of their oxygen, sulfur, and selenium analogs. The peculiar chemical behavior caused by the presence of a tellurium center is most clearly manifested in the reaction of tellurapyrylium cations bearing dimethylamino groups with halogens. 

Like their sulfur congener, selenium and tellurium can form polyatomic cations and anions in many compounds. 

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