The influence of acetonitrile on complex formation of crown ethers containing different donor atoms

The complexation reactions of crown ethers with monovalent cations and Ba²⁺ were studied in acetonitrile solutions by means of calorimetric and potentiometric titration. The reaction enthalpies measured clearly demonstrate the influence of the interactions between 18-crown-6 and the acetonitrile solvent molecules. Changing the donor atoms or other substituents on the ligand molecule can exert a strong influence on the interactions with the solvent. Thus, all the reaction enthalpies measured for the reaction of 15-crown-5 with different cations are higher compared with 18-crown-6. On comparison with results in methanol, an approximate estimation is made of the influence of solvent molecules on the reaction enthalpies measured in acetonitrile. Due to the strong interaction between silver ion and acetonitrile, complex formation is only observed with crown ethers containing additional nitrogen or sulphur donor atoms.