THE COMPLEXATION OF THE AMMONIUM ION BY 18-CROWN-6 IN DIFFERENT SOLVENTS AND BY NONCYCLIC LIGANDS, CROWN-ETHERS AND CRYPTANDS IN METHANOL

The complexation of the ammonium ion with the macrocyclic ligand 18-cr own-6 was studied using calorimetric and potentiometric titrations in different solvents. In water and dimethyl sulphoxide the stability con stants had the lowest values compared with all other solvents examined . No specific interactions between the ammonium ion and solvent molecu les were observed. Crown ethers formed more stable complexes in methan ol with the ammonium ion than diaza crown ethers. The most stable comp lexes were formed with cryptands. The highest values of the stability constants for the reaction with macrocyclic and macrobicyclic ligands were measured if the dimensions of the ammonium ion and of the cavitie s were nearly identical. (C) 1998 Elsevier Science Limited.