In distinction to aqueous copper acetate solutions spectra of the

The water–ammonia copper salt solutions have a more complicated composition of copper complexes. After the addition of ammonia solution to the aqueous copper acetate solution, precipitation of copper hydroxide is observed, which is followed by its dissolution with the formation of ammonia–copper complexes [Cu(NH3)n(H2O)6-n]2+ (so-called Schweitzer's reagent). The composition of ammonia–copper complexes depends on the NH4+/Cu2+ ratio and pH of the medium. The NH3 amount increases with raising the pH and NH4+/Cu2+ ratio; this provokes consecutive substitution of H2O and OH− ligands in the coordination sphere of Cu2+ Nocodazole by ammonia ligands. Thus, the [Cu(NH3)3(H2O)3]2+ and [Cu(NH3)4(H2O)2]2+ complexes are predominant at pH 7–8 and 8.5–10.5, respectively; at pH > 10 the [Cu(NH3)4(H2O)2]2+ is coexisted with [Cu(NH3)5(H2O)2]2+ complex [25] and [26]. Note that among copper ammine complexes most stable is the [Cu(NH3)4]2+ complex (β2 = 7.9 × 1012). It cannot be ruled out that at a low ammonia concentration (NH4+/Cu2+ < 4) in the solution not only the ammonia–copper complexes are present but also the [Cu(H2O)5(OH)]+, [Cu2(OH)2(H2O)8]2+ and polynuclear hydroxocomplexes. After the formation of tetraammine complex at NH4+/Cu2+ near 6–15 the concentration of Cu2+ ions is quite low and insufficient for attaining the product of copper(II) hydroxide solubility equal to 5.6 × 10−20. On the other hand, in a strongly alkaline medium (NH4+/Cu2+ > 20, pH > 12.5) the formation of CuO is possible due to a decreased stability of soluble ammonia copper complexes [25]. In addition, the high ammonia concentrations can cause desilication of the zeolite surface, which is desirable to avoid. This is why the ion exchange is necessary performed using the ammonia solutions of copper salts with pH 10.0–11.0.