Effect of Dielectric Constant of the Medium on Stability Constants of 4,5-Dihydro Substituted Oxazoles in DMF -Water Mixture

The effect of the dielectric constant of the solvent medium on the stability constants of metal–ligand complexes has been systematically studied for 1,4-dihydro substituted oxazoles with Co (II) and Sm (III) metal ions in mixed solvent systems of N, N-dimethylformamide (DMF) and water at 30 ± 0.1 °C and constant ionic strength. The dielectric constant of the medium was varied by changing the proportion of DMF in the DMF–water mixture. The proton-ligand and metal-ligand stability constants were determined potentiometrically using the Irving–Rossotti method. The results reveal that the stability constants of the complexes decrease with decreasing dielectric constant of the medium. This behavior is attributed to reduced solvation of the ions and increased electrostatic repulsion between charged species in less polar environments. The observed trend suggests that complex formation is favored in highly polar media, where greater ion–dipole interactions and stabilization of charged intermediates occur. The results are discussed in terms of solvent polarity, solvation effects, and the electronic environment around the metal center.