Copper sulphate and ammonia reaction. Copper sulphate (blue, in beaker at right) in solution has copper ions bonded by four molecules of water, which are known as ligands when bonded this way. This forms the complex Cu[(H2O)4]2+. When ammonia (NH3, left) is added, it replaces some of the water ions and forms the complex Cu([NH3]4[H2O]2)2+, which is dark blue.