Ionization isomers are a type of isomerism observed in coordination compounds. They occur when there is a rearrangement of ligands between the coordination sphere and the ionization sphere of the complex. For example, consider the isomers [Co(NH3)5SO4]Br and [Co(NH3)5Br]SO4, where the positions of the sulfate ion (SO4²⁻) and bromide ion (Br⁻) in the coordination sphere are interchanged