Cations halogen

The existence of many well-known compounds in which chlorine, bromine, and iodine are found in the +1 oxidation state led to the assumption that the cations Cl+, Br+, and I+ are important and stable entities or at best as reaction intermediates. However, no evidence exists for monoatomic Cl+, Br+, and I+ as stable species.771,772 In contrast, a whole series of polyatomic halogen cations are known.773-776 

Iodine Cations. The existence of I3+ and I5+ ions, deduced by Masson777 

70 years ago in aromatic iodination reactions, has been confirmed now by physical measurements. The controversy over the nature of blue solutions of iodine in strong acid media has now been settled. It has been shown conclusively that these solutions contain I2 ions and not I as suggested earlier. 

Solutions of I3 in 100% sulfuric acid or fluorosulfuric acid dissolve at least 1 

On the basis of 127I nuclear quadrupole resonance (NQR) studies of I31 AICI, , Corbett and co-workers785 have predicted a bond angle of 97° between the two bonding orbitals on the central atom. X-ray crystal structures of I31 AICI and I5 SbF6 have been obtained. In the latter salt, two cations are weakly bound to a 

Force constant k in newton/metre 1 millidyne/A = lOONm.  

More recently a simpler route has been devised which involves oxidation of Bt2 or I2 with the peroxide S2O6F2 (p. 640) followed by solvolysis using an excess of SbFs, e.g.  

During the past 20 y numerous other highly coloured halogen cations have been characterized by Raman spectroscopy. X-ray crystallography, and other techniques, as summarized in Table 17.18. Typical preparative routes involve direct oxidation of the halogen (a) in the absence of solvent, (b) in a solvent which is itself the oxidant (e.g. AsFs) or (c) in a non-reactive solvent (e.g. SO2). Some examples are listed below  

Other compounds that have been prepared include the dark-brown gold(III) complexes 

The triatomic cations X3+ are nonlinear and thus isostructural with other 20-electron species such as XY2+ (p. 839) and SCI2 (p. 689). The contrast in bond lengths and angles between I3+ (Fig. 17.15) and the linear 22-electron anion I3 (p. 836) is notable, as is its similarity with the isolectronic Tc3 anion (p. 764). Likewise, Br3Asp6 is isomorphous with I3ASF6 and the non-linear cation has Br Br 227.0 pm and an angle of 102.5° (cf. Br3 , Table 17.15). The structures of the penta-atomic cations Brs+ (2) and I5+ (3) have been determined by X-ray analysis of their AsFe salts and shown to have centrosymmetric Cjh symmetry like the 

The Halogens Fluorine, Chlorine, Bromine, Iodine and Astatine 

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Table 2 Characterized examples of binary sulfur, selenium, and tellurium halogen cations...

Half-lives, of selected actinide nuclides, 614 Halides, 308. 309. 848-852 Halogen cations, 847-848 Halogen oxides, 846-847 Halogens, 824 electrochemistry of, 853 heavier, oxyacids of, 845-846 physical inorganic chemistry of, 848... 

Halohydrins are useful intermediates especially in the synthesis of epoxides. The main reaction is usually accompanied by the formation of a dihalide. When the reactions are performed in the presence of acetic acid, then acetates of the hydrins can be the predominant products. With several exceptions, alkenes with a nonfluorinated C = C bond have been subjected to halohydrinations. Halogen cations usually undergo addition to the substituted carbon of the C = C bond in (fluoroalkyl)ethenes. 

The structures of the following homopolyatomic halogen cations have been determined by X-ray analysis ... 

There has always been considerable interest in the halogen cations and it has often been postulated that the simple ions I+, Br+, and Cl+ are the reactive intermediates in aromatic halogenation reactions. No convincing evidence has ever been obtained for these cations however, the search for them has led to the discovery of the I cation and a number of other related halogen cations (Gillespie and Morton, 1970) which are stable in superacid media. The I cation can be conveniently prepared by the oxidation of I2 with S206F2 in solution in HSOsF. 

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