Complex ionA complex ion is a polyatomic ion formed by a charged complex between one or more metal atoms associated through coordinate-covalent bonds to one or more non-metallic ligands.
The ligands may, in turn, be either simple ions, polyatomic ions, or neutral polyatomic molecules.
Complexation may alter the chemical properties of Ions, for example Cu2+ solved in water is light blue, and [Cu(NH3)4]2+ is dark blue.
Silverchloride is (virtually) unsoluble in water. When Ammonia is added, it "vanishes" immediately:
AgCl + 2 NH3 --> [Ag(NH3)2]+ + Cl-