Homopolyatomic Cations of the Elements

In their review Gillespie and Passmore [49] describe homopolyatomic cations of metallic elements such as Bi, Hg, Cd and Zn and these have been discussed more recently [4(d)], Many of these were isolated initially as naked cations from molten salt mixtures by reacting the metal with its normal chloride directly or in a host melt. The cation Hg,+ has been known for 100 years. It was not then so surprising when... 

The preparation and properties of homopolyatomic cations of the Group VI elements have been reviewed recently.1 The general method described below, involving the oxidation of elemental sulfur, selenium, and tellurium with either antimony pentafluoride or arsenic pentafluoride in liquid sulfur dioxide, is convenient for the preparation of compounds containing these polyatomic cations. The procedure is basically that briefly described previously2 for the preparation of Se8(Sb2F j i )2. 

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). 

The major synthetic strategies for preparing homopolyatomic cations of group 16 elements can be summarized as follows ... 

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. 

The apparent Instability of homopolyatomic anions of elements to the left of group IV (and of polyatomic cations to the left of group V) Is thought to result from a deficiency of bonding electrons In species where the principal bonding Is considered to originate largely from p-type orbitals. The electron deficient polyboranes, with which these clusters have... 

Salts of homopolyatomic cationic clusters now constitute a well-established class of compound— there are at least twenty-six fairly well-characterized examples. It is probable that many other elements will also be shown to form polyatomic cations. As yet reactions of these species have been little studied, and there is obviously a wide open field here awaiting exploration. Many structures of known cations, as well as those that have not yet been prepared, remain to be investigated, and there is a need for theories that can predict the stability and geometry of these cations and provide a description of the bonding. 

Homopolyatomic cations are named by adding the charge number to the stoichiometric name of the corresponding neutral species, i.e. the element name with the appropriate multiplicative prefix. Radical dots may be added to indicate the presence of unpaired electrons. 

---