Complex Formation of Alkaline-Earth Cations with Crown Ethers and Cryptands in Methanol Solutions

Article abstract of DOI:10.1007/BF00644888

The complexation of alkaline-earth cations by different crown ethers, azacrown ethers, and cryptands has been studied in methanol solutions by means of calorimetric and potentiometric titratios.The smallest monocyclic ligands examined form 2:1 complexes (ratio of ligand to cation) with cations which are too large to fit into the ligand cavity.With the smallest cryptand, only Sr²⁺ and Ba²⁺ ions are able to form exclusive complexes.In the case of the reaction of cryptand (211) with Ca²⁺, a separate estimation of stability constants for the formation of exclusive and inclusive complexes was possible for the first time.Higher values for stability constants are found for the reaction of alkaline-earth cations with cryptands compared to the reaction with alkali ions.This increase is only caused by favorable entropic contributions.