Iodine trichloride dimer

The interhalogen compounds obey the expectations based on the VSEPR theory, and typical structures are giver in Chapter 6. Ore compound not included there is the dimeric iodine trichloride, in which the iodine atom of the monomeric species appears to act as a Lewis acid and accept an additional pair of electrons from a chlorine atom (Fig. 17.5). 

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). 

Iodine monobromide, a solid resulting from direct combination of the elements, is endothermic and extensively dissociated in the vapor. It is used instead of Br2 in some industrial processes. Despite the general instability of the BrX compounds, the fluorosulfate (BrOS02F) obtained by treating Br2 with S206F2, is stable to 150°C. Iodine trichloride (IC13) is also formed (like IC1) by treatment of liquid chlorine with the stoichiometric quantity of iodine, or with a deficiency of iodine followed by evaporation of the excess of chlorine. It is a fluffy orange powder, unstable much above room temperature, with a planar dimeric structure (13-VIII). 

The diphenyliodine(III) halides have dimeric structures in the solid state,63 directly comparable with that of IC13.29 Thus, these compounds have a planar coordination of the iodine atom by two carbon and two bridging halogen atoms. This corresponds to the 12-electron, octahedral arrangement. The I—Cl bonds in the chloride, of 3.085 A, are longer than those of 2.70 A in the trichloride and presumably reflect the significance63 of the ionic form [Ph2I]+[Cl] 2. 

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