A Review of the Thermodynamics of Complexation of Crown Ethers With Metal Ion

Recently, macrocyclic and supramolecular chemistry has reached a hopeful area of research in the mutual interaction between chemistry, physics and biology. Charles J. Pedersen, at du Pont figure out a compound in the early 1960s famous for dibenzo-18-crown-6 (DB18C6) later on. The detection of the complex formation in solution, the designation of the stability of the consequence complex or complexes and the determination of the thermodynamic or the kinetic parameters of the complex formation can be attained by a manifold of physicochemical measurements. Conformational rigidity or flexibility of macrocycles has a considerable penetration on their selective behavior. The number, type, and arrangement of donor atoms in the macrocyclic rings play a main role in macrocycle selectivity. Based on chemistry terminology, this is known as “host-guest” chemistry where the ether plays the role as the host and the ionic species as the guest. In organic solutions, crown ethers take the role of phase-transfer catalysts and agents in order to enhance the solubility of inorganic salts. Macrocycles need to compete with solvent molecules for the cations during the process of complexation. Consequently, variation of the solvent makes a considerable change in the manifest binding characteristics of these ligands.