The complexation reactions between alkali and alkaline-earth metal cations with DB18C6 were studied in acetonitrile–methanol (AN–MeOH) and tetrahydrofuran–threechloromethane (THF–CHCl 3 ) binary mixtures at different temperatures using the conductometric method. The obtained results show that in most cases, the DB18C6 forms 1 : 1 complexes with these metal cations and the stability of the complexes is affected by the nature and composition of the mixed solvents. The stability order of complexes in AN–MeOH binary systems was found to be Na + > Li + , and in the case of THF–CHCl 3 binary mixtures was Na + > Ba 2+ > Li + . An anomalous and interesting behavior was observed for the case of complexation of a K+ ion with DB18C6 in the AN–MeOH binary mixture and also for complexation of Mg 2+ and Ca 2+ cations with this ligand in pure THF and also in THF–CHCl 3 binary systems. The values of the thermodynamic parameters (∆ and∆ ) for complexation reactions obtained from the temperature dependence of the stability constants and the results show that the complexes are both enthalpy- and entropy-stabilized.

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