Interhalogen Compounds

compounds formed by the reaction of one halogen with another.

The known interhalogen compounds are classified as fluorides (C1F, C1F₃, BrF, BrF₃, BrF₅, IF, IF₅, and IF₇), chlorides (BrCl, ICl, and ICl₃), and bromides (IBr). There are usually no more than two elements in an interhalogen compound. As a rule, halogens form interhalogen compounds such that the farther apart the halogens are in Mendeleev’s periodic table, the greater the number of atoms in the resulting molecule. All interhalogen compounds can be synthesized by the chemical reaction of the elements of the halogen family. Furthermore, the compounds whose composition can be expressed by the formulas AB₃ through AB₇ are formed by the addition of the appropriate halogens to AB interhalogens.

Under normal conditions, CIF, CIF₃, and IF₃ exist in the gaseous state, and IC1, IC1₃, IBr, and BrClFe₆ occur as solids. All other interhalogen compounds exist naturally as liquids. The least stable of the interhalogen compounds are BrF and BrCl; the other compounds are relatively stable under normal conditions, although they dissociate to a greater or lesser degree at temperatures of 25°-50°C.

Interhalogen compounds have physical and chemical properties similar to those of free halogens; however, they are polar, since they are composed of elements exhibiting different degrees of electronegativity. For example, the electric conductivity of solid and liquid interhalogen compounds is considerably higher than that of halogens, and in solutions and melts the molecules of interhalogens are always associated.

Certain interhalogen compounds show a higher degree of chemical activity than do their component halogens; for example, CIF is more reactive with many organic compounds than is free fluoride. Characteristically, interhalogen compounds have a marked capacity for forming complexes with inorganic halides (for example, KCL·IC1 and BrF₃·SbF₃) and with organic substances (aniline, pyridine, and dioxane). The uses of interhalogen compounds are basically limited to quantitative chemical analysis, which makes use of hydrochloric IC1 and ICl₃.