Effect of molecular vibrations on the selectivity character of pyridino-18-crown-6 derivatives towards potassium ion

► Interaction of flexible and rigid crown ether towards K+ ion has been investigated. ► Thermodynamic parameters have been calculated applying van't Hoff equation. ► Entropy decreased slightly in case of formation of flexible crown ether K+ complex. ► Entropy increased in case of formation of rigid crown ether K+ complex. ► Molecular vibrations are responsible for the entropy changes at molecular level.