Copper(II) complex formation (Part 2)

The ligands are added in order of increasing complex stability, so we expect a ligand exchange reaction to take place on each addition. Firstly, the ammonia replaces the water in the copper-aquo complex to give the royal blue tetrammino complex. Then the 2-hydroxybenzoate ions replace the ammonia molecules to form the green 2-hydroxybenzoate complex. The ligands in this complex are then replaced by edta ligands to produce the sky blue edta complex. Finally, the most stable 1,2-dihydroxybenzene complex is formed by replacement of the edta ligands, and a green-brown colour results.