Polyselenium cations

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)]. 

The addition of selenium to the yellow solution up to a 8 1 ratio of Se S2OgF2 did not appreciably affect the conductivity. This indicated that the FS03 ion concentration remained unchanged and that the Se42+ ion is reduced by selenium to Seg2+ 344 [Eq. (4.220)]. 

Conductivity measurements of selenium in pure fluorosulfuric acid were also consistent with the formation of Seg2+ 344. 

Solutions of Se8+ in 100% H2S04 may be prepared by heating selenium in the acid at 50-60°C the element is oxidized by sulfuric acid [Eq. (4.221)]. The Se42+ 343 can also be oxidized to Se82+ 344 by selenium dioxide. 

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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). 

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

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