Neutral interhalogen compounds

The halogens form many compounds and ions that are binary or ternary combinations of halogen atoms. There are three basic types (a) neutral interhalogen compounds, (b) interhalogen cations, and (c) interhalogen anions. 

The halogens react with each other to form binary interhalogen compounds XY, XY3, XY5 and XY7, where X is the heavier halogen. A few ternary compounds are also known, e.g., IFCI2 and IF2CI. All interhalogen compounds contain an even number of halogen atoms. Table 17.2.1 lists the physical properties of some XYm compounds. 

XY All six possible diatomic interhalogen compounds between F, Cl, Br and I are known, but IF is unstable, and BrCl cannot be isolated free from Br2 and CI2. In general, the diatomic interhalogens exhibit properties intermediate 

Iodine trichloride is a fluffy orange powder that is unstable above room temperature. Its dimer (ICH3)2 has aplanar structure, as shown in Fig. 17.2.1(c), that contains two I-Cl-I bridges (I-Cl distances in the range of 268-272 pm) and four terminal I-Cl bonds (238-9 pm). 

XY7 IF7 is the sole representative of this structural type. Its structure, as shown in Fig. 17.2.1(e), exhibits a slight deformation from pentagonal 

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The halogens combine with each other to form four types of binary, neutral, interhalogen compounds XY (all possible combinations), XY3 (Y = F only), XY5 (Y = F only), and XY7 (X = I and Y=F only), where X is the heavier halogen (Table VI). The greater the electronegativity difference (Table HI) between the central atom X and the terminal atoms Y, the greater the total number of Y atoms that can be bound in the molecule. Thus, iodine can bind up to seven F atoms, but only a maximum of three Cl atoms or one Br atom. The structures of these molecules can generally be predicted by simple valence-shell electron-pair repulsion (VSEPR) theory, in which the bonded and... 

Neutral electrophiles contain a highly polarized E-X bond therefore, they are able to participate in electrophilic reactions. Interhalogen compounds... 

Ion of 1 — charge Neutral dimeric species Hydrohalic acid Formation of interhalogen compounds... 

Some interhalogen compounds form as well, and they form an extensive array of both neutral and cationic compounds with each other. These can be diatomic (CIF, BrF, IF, BrCl, ICl, and so on), tetratomic (CIF3, BrFj, IF3, and so on), hexatomic (CIF5, BrF, IF5, and so on), and even octatomic in the case of iodine heptaflouride (IF ). 

A few ternary compounds, such as IFCI2 and IF2CI, are also known. As can be seen from the formulas, the neutral interhalogen molecules always contain an even number of halogen atoms. A variety of polyhalide ions have also been identified. Many contain an odd number of halogen atoms. 

The halogens involved may or may not be of the same kind. Although compounds formed from these anions tend to be unstable, decomposing to a metal halide and neutral halogen or interhalogen molecule, stabilities may be enhanced by the presence of large cations, such as Cs+ or tetraalkylammonium ions (R4N+). 

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