Thermodynamic study for dicyclohexano-24-crown-8 complexes with K+, Rb+, Cs+ and Tl+ ions in binary acetonitrile nitromethane mixtures by conductometric method

The complexation reactions between dicyclohexano-24-crown-8 (DC24C8) and K-+,K- Rb-+,Rb- Cs+ and Tl+ ions were studied conductometrically in the different acetonitrile-nitromethane mixtures 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 degrees C and in all solvent mixtures used, the stability of the resulting complexes varied in order of Tl+ > K+ > Rb+ similar to Cs+. The enthalpy and entropy changes of the complexation reactions were evaluated by the temperature dependence of formation constants. It was found that the stability of the resulting complexes increased with increasing nitromethane in the solvent mixture.