When ammonium hydroxide is added in excess in copper chloride solution, first a precipitate of cupric hydroxide is formed which then redissolves forming tetrammine copper (II) chloride.
CuCl2+2NH4OH→Cu(OH)2↓+2NH4Cl
Cu(OH)2+4NH4Cl→[Cu(NH3)4]⋅2Cl+2H2O+2HCl