Cations catenated

The propensity for iodine to catenate is well illustrated by the numerous polyiodides which crystallize from solutions containing iodide ions and iodine. The symmetrical and unsymmetrical 13 ions (Table 17.15) have already been mentioned as have the I5- and anions and the extended networks of stoichiometry (Fig. 17.12). The stoichiometry of the crystals and the detailed geometry of the polyhalide depend sensitively on the relative concentrations of the components and the nature of the cation. For example, the linear ion may have the following dimensions ... 

This review has shown the complexity of the chemistry and the electrochemistry of sulfur, polysulflde ions, and sulfur cations. This complexity originates from the ability of sulfur to form catenated species, which leads to disproportionation and dissociation equilibria. 

There are no well-characterized polymeric bismuth catenates, although a black ether-insoluble substance, described as (PhBi)x, results from the reduction of phenylbismuth halides with LiAlH4.200 A polymeric bismuthine is thought to result from the decomposition of l,T-bibismolane.201 To date, bismuth catenation is limited to Bi2 in the case of free molecules and to some complex anionic and cationic clusters. 

Mercury forms a unique series of catenated polyatomic cations Hgj + that can be considered as complexes having monatomic Hg° as a ligand. These cations are the subject of Section 11.3. 

By comparison with the mercury(I) and mercury(II) ions (Chapter 56.1), the coordination chemistry of (10) and (11) has received little attention. Both ions disproportionate to Hg° and Hg2+ /Hg2+ in media more basic than those from which they can be prepared. However, the existence of (11) (which can be regarded as a complex of (10) with Hg°) and the cation-anion coordination found in solid salts of (10)38 suggest that this ion, at least, might form stable complexes with suitable weak donors. In addition, the formation of as yet incompletely characterized Hg2BrCI04 2SnBr2, which may contain both Hg—Hg and Hg—Sn bonds,42 and the isolation and characterization of [ (np3)Co HgHg Co(np3) ] (1 see Section 11.2) may presage a wider occurrence of catenated heterometallic polymercury species. Slow disproportionation of (11) into (10) and Hg3-X(MF6) occurs even in liquid S02.39 As discussed below, there is evidence for mercury atom transfer between (10) and (11) in liquid S02. 

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