The halogens react with each other to form interhalogen compounds.
The general formula of most interhalogen compounds is XYn, where n = 1, 3, 5 or 7, and X is the less electronegative of the two halogens. They are all prone to hydrolysis, and ionise to give rise to polyhalogen ions. No ternary (containing three different halogens) interhalogen compounds are known.
Read more about Interhalogen: Diatomic Interhalogens, Tetratomic Interhalogens, Hexatomic Interhalogens, Octatomic Interhalogens, Summary of Known Interhalogens