Chemistry

These two complexes differ only in their counter-ion (the anion outside the coordination sphere), while the actual metal-ligand core—the $[Co(NH_3)_5(SO_4)]^+$ cation—remains identical. This is the key to recognizing isomerism: specifically, ionization isomerism, where compounds have the same molecular formula but different ions in solution because different anions are incorporated into or excluded from the coordination sphere. The bromide and chloride versions will show different chemical properties (like conductivity and precipitation reactions) even though their central complex is the same.

These two complexes differ only in their counter-ion (the anion outside the coordination sphere), while the actual metal-ligand core—the $[Co(NH_3)_5(SO_4)]^+$ cation—remains identical. This is the key to recognizing isomerism: specifically, ionization isomerism, where compounds have the same molecular formula but different ions in solution because different anions are incorporated into or excluded from the coordination sphere. The bromide and chloride versions will show different chemical properties (like conductivity and precipitation reactions) even though their central complex is the same.