How are interhalogen compounds formed?

An inter-halogen compound is a molecule which contains two or more different halogen atoms (fluorine, chlorine, bromine, iodine, or astatine) and no atoms of elements from any other group. Most inter-halogen compounds known are binary. Their formulae are generally XYn, where n is 1, 3, 5 or 7, and X is the less electronegative of the two halogens. Types of interhalogens are: Diatomic interhalogens, Tetratomic interhalogens, Hexatomic interhalogens, Octatomic interhalogens