Homopolyatomic 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. 

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

Solovothermal techniques have also recently been employed. For instance, the reactions of Te with WCU and of Te, TeCl4 and NbCls in SnCl4 at 150 °C afford the compounds [Te6][Te8](MCU)4 (M = W, Nb) [19] with boat shaped Te62+and Te82+ in a bicyclo[2.2.2]octane geometry. 

The structures of individual polychalcogen cations and theoretically based interpretations of their bonding will now be discussed in order of increasing nuclearity n = 4-19. For more details, the reader is referred to the excellent recent review articles of Beck [19] (structures) and Passmore [13] (bonding and energetics). 

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Direct Synthesis reaction of, 6 395 fluoride, 21 235, 237, 239, 249 homopolyatomic cations, 17 82 ion, stereochemistry, 2 40-41, 44-45 isocyanates, preparation, 9 158 properties, 9 157 isothiocyanates, properties, 9 177 mixed valence compounds of, 10 375-381 crystal structure of, 10 376 diffuse reflectance spectrum of, 10 380 structure of Pb," ion, 10 381 nuclear magnetic shielding, 22 224 organometallic compounds, 2 82, 88, 89 oxide, neutron diffraction studies on, 8 231-233... 

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. 

Figures 16.8.2(h), (i), and (j) show the structures of Se2J, Se2+, and Se, respectively. They all consist of seven- or eight-membered rings connected by short chains. Each homopolyatomic cation has two three-coordinate atoms that formally carry the positive charges. Se2g has a bicyclo[2.2.4]decane geometry. The Se-Se bond distances vary between 225 and 240 pm, and the Se-Se-Se angles range from 97° to 106°. Se2+ and Se2+ comprise a pair of seven-membered rings connected by a three- and four-atom chain, respectively.

The main use of CF3SO3H in synthetic inorganic chemistry reported to date has been in preparation of binary compounds which are themselves triflates or of complexes derived from those triflates. HSO3F has been used similarly in the generation of fluorosulfates and of fluorosulfato-complexes but it has also been the medium of choice, particularly when coupled with the oxidant S206F2, in the generation and characterisation of many homopolyatomic cations and transition metal carbonyl cations, as will be shown in Sec. 11.3.4. 

Stability of homopolyatomic cations of chalcogen elements in superacid media... 

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... 

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