The stepwise formation constants for complexes of NH2CH2CH2NH2 (en) with [Cu(OH2)6]2+ (aq) are log Kf1 = 10.72 and log Kf2 = 9.31. The stepwise formation constants for complexes of NH3 with [Cu(OH2)6]2+ (aq) are log Kf1 = 4.15, log Kf2 = 3.50, log Kf3 = 2.89, log Kf4 = 2.13, and log Kf5 = -0.52. Compare the values for both substitution reactions and suggest why they are different.