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

Abstract

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.

Revisiting Dynamic Processes and Relaxation Mechanisms in a Heterocyclic Glass-Former: Direct Observation of a Transient State

“…Under these conditions, the unreacted free chemical individua remain in thermal equilibrium with the formed complex salts of various geometries, which is quantified by a stability constant. 58 According to the DFT calculations, the complexation of Pd 2+ by MeBzS 2 in geometries close to conformers M1 or M2 is ineffective and leads to unstable higher-energy structures (Figure 6a). In turn, transient conformations T1* and T2* are the most energetically privileged geometries of MeBzS 2 in the presence of PdCl 2 (Figure 6a).…”

“…In general, the complexation of metal cations by organic ligands can occur in a solution. Under these conditions, the unreacted free chemical individua remain in thermal equilibrium with the formed complex salts of various geometries, which is quantified by a stability constant . According to the DFT calculations, the complexation of Pd 2+ by MeBzS 2 in geometries close to conformers M1 or M2 is ineffective and leads to unstable higher-energy structures (Figure a).…”