engleski

Solvation Effect on the Complexation of Cations by Lower-Rim Calix[4]arene Derivatives

Complexation of alkali and alkaline earth metal cations in several solvents was studied by means of an integrated thermodynamic, structural, and computational approach.1 The solvents were chosen taking into account the differences in their cation and ligand solvation abilities and the possibility of ligand-solvent and complex-solvent hydrogen bonding. The thermodynamic data (complex stability constants and derived reaction Gibbs energies, reaction enthalpies and entropies), determined by means of UV and NMR spectroscopies, fluorimetry, potentiometry, conductometry, and microcalorimetry, were correlated with the structural results obtained by X-ray crystallography, NMR, and computational methods (DFT and molecular dynamics). The solvation and transfer parameters of the ligands and their complexes were also determined and discussed. The intra- and intermolecular hydrogen-bonding and solvent effects (especially specific solvent- solute interactions) on the equilibria of the binding reactions were particularly addressed. The results of the above-mentioned studies clearly indicated how remarkable and complex the influence of the solvent on the ion-hosting abilities of the calixarene derivatives can be. They also suggested that integrated and comprehensive experimental and computational investigations can indeed provide a rather detailed insight into the ligand properties and reactivities, i.e. the factors governing the complexation processes.

calixarenes ; cations ; coordination reactions ; solvation ; thermodynamics

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