The complexation reactions between dibenzopyridino-18-crown-6 and Tl+, K+, Sr2+ and Ba2+ ions were studied conductometrically in acetonitrile solution at various temperatures. The formation constants of the resulting 1:1 complexes were calculated from the computer fitting of the molar conductance-mole ratio data at different temperatures. At 25°C, the stability of the resulting complexes varied in the order Ba2+ > Sr2+ > Tl+ > K+. The enthalpy and entropy changes of the complexation reactions were evaluated from the temperature dependence of formation constants. While, the bivalent alkaline earth complexes are both enthalpy and entropy stabilized, the univalent cation complexes used are enthalpy stabilized but entropy destabilized.
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