A COMBINED EXPERIMENTAL AND DENSITY FUNCTIONAL THEORY STUDY ON THE COMPLEXATION ABILITY OF 15-CROWN-5 WITHLI ⁺, NA⁺, K⁺, AND NH₄⁺ CATIONS

The complexation processes among Li+, Na+, K+, and NH4^o+o cations with the macrocyclic ligand, 15-crown-5 (15C5) have been studied in acetonitrile–methanol binary mixtures at different temperatures using conductometric method. The stability constants of the resulting 1: 1 complexes were calculated from the computer fitting of the molar conductance–mole ratio data at various temperatures. The values of thermodynamic parameters (\unicodex0394H?cand\unicodex0394S^?c) for the formation of the complexes were obtained from temperature dependence of the stability constants of complexes using van’t Hoff plots. In addition, a theoretical study has been carried out using density functional theory to obtain the stability of the complexes and the geometrical structure of the 15C5 and its complexes with Li+, Na+, K+ and NH4^o+o cations in the gas phase. We compared the experimental data with those obtained by quantum chemistry calculations to investigate the effect of the solvent on complexation process.