Abstract
The complex formation of Co 2+ and Ni 2+ with various noncyclic ligands, aza crown ethers and cryptands has been studied in methanol by means of calorimetric and potentiometric titrations. The reactions of both cations with aza crown ethers were endothermic. This surprising result can be explained by structural changes of the ligand during the complexation process. The thermograms for the titration of Ni 2+ solutions with cryptands show two different reactions. On the basis of further results from potentiometric titrations, a two-step reaction mechanism is discussed. The macrocyclic and the cryptate effect are only caused by favourable entropic changes.
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