Complex ion

A 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^-