Answer: Chelating ligands often form more stable complex
Chapter 19, Problem 19.85(choose chapter or problem)
Chelating ligands often form more stable complex ions than the corresponding monodentate ligands form with the same donor atoms. For example, Ni21(aq) 1 6NH3(aq) 34 Ni(NH3)6 21(aq) Kf 5 3.2 3 108 Ni21(aq) 1 3en(aq) 34 Ni(en)3 21(aq) Kf 5 1.6 3 1018 Ni21(aq) 1 penten(aq) 34 Ni(penten)21(aq) Kf 5 2.0 3 1019 where en is ethylenediamine and penten is O G G D D N CH2OCH2ON NH2CH2CH2 NH2CH2CH2 CH2CH2NH2 CH2CH2NH2 The increased stability that results is called the chelate effect. From the bond energies, would you expect the enthalpy changes for the preceding reactions to be very different? What is the order (from least favorable to most favorable) of the entropy changes for the preceding reactions? How do the values of the formation constants correlate with DS8? How can this be used to explain the chelate effect?
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