Silver complexes with large crown ethers in propylene carbonate

The complex formation between large crown ethers – e.g. dibenzo-30-crown-10 – and Ag+ in propylene carbonate has been studied using potentiometric and calorimetric titrations. The values of the reaction enthalpies with larger crown ethers than 18-crown-6 especially with dibenzo-30-crown-10 indicate that more than six donor atoms are taking part in the interaction with the complexed cation. The values of the reaction entropies of the largest crown ethers examined indicate the high sterical requirements of the complex formation. Obviously large crown ethers are able to encapsulate the complexed cation. The effectiveness of the encapsulation however depends upon the ring size and flexibility of the crown ethers.