Polyselenium

Aluminum forms a complete series of AlYX compounds (Y = S, Se, Te X = Cl, Br, I). Furthermore, a number of compounds with Se(IV) and Te(IV) are known, such as TeClJ AlClj (197) and SeClJ AICI4 (364), which are not considered here. A borderline case consists in the reduced phases found in the systems (TeCl4-(-4AlCl3)-Te and (SeCl4 + 4A1C13)-Se (88), e.g., Te (AlCl4-)2 (89), Te + (Al Clf)2 (89), Te + (AlCli-) (88), Se5+ (AlClj) (88), and Se + (AlClj)2 (87), which contain cyclic pol3dellurium and polyselenium cations. For a detailed review of homopolyatomic ions of the posttransition elements, see (86). 

When colloidal selenium was heated with mercuric trifluoroacetate or silver trifluoroacetate, bis(trifluoromethyl)diselenide was formed (43). Later work with selenium/silver carboxylate, RC02Ag (R = CF3, C2F5, or C3F7), mixtures at 280° C in a vacuum produced a mixture of the bis(perfluoroalkyl)selenide and the bis(perfluoroalkyl)diselenide (44). Formation of a polyselenium trifluoroacetate, which decarboxylates to produce the trifluoromethylselenides, was the proposed mechanism for R = CF3 (44). However, silver trifluoroacetate is a source of trifluoromethyl radicals when heated above 260° C (21), hence the trifluoromethylselenides may be formed by reaction of trifluoromethyl radicals with selenium, as in the reaction of CF3I with selenium [Eq. (34)] (45). 

Further information of the chemistry of polysulfur, polyselenium, and polytellurium cations can be found in reviews.773 776,876,898 899... 

Polyselenium cations are less electrophilic than their sulfur analogs and give stable solutions in various strong acids.902 In fluorosulfuric acid, selenium can be oxidized quantitatively by S206F2 to give yellow Se42+ 343 [Eq. (4.219)]. 

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