The complexation reaction of 18-crown-6 with Ag+ in different solvents studied by potentiometric and calorimetric methods

The complexation of the silver ion with the macrocyclic ligand 18-crown-6 was studied using calorimetric and potentiometric titrations in different solvents. In water, dimethylsulfoxide, 1,3-dimethyl-2-imidazolidinone and acetonitrile, the stability constants have the lowest values compared with all other solvents examined. In propylene carbonate, acetone and 2,2,2-trifluoroethanol the most stable complexes are formed. The strength of solvation of the silver ion is responsible for the stability of the complexes formed. A correlation between the single ion standard molar Gibbs free energies of transfer (ΔGtr) of Ag+ from water to the other solvents and the complex stabilities is observed. In the solvent acetonitrile additional interactions between 18-crown-6 and the solvent molecules are responsible for the small stability constant.