COMPLEXATION OF SODIUM, POTASSIUM, RUBIDIUM, CESIUM AND AMMONIUM-IONSWITH 12-CROWN-4 IN N,N-DIMETHYLFORMAMIDE AND WATER

The complexation of 1,4,7,10-tetraoxacyclododecane (12-crown-4) with s odium, potassium, rubidium, cesium and ammonium ions has been studied by titration calorimetry in N,N-dimethylformamide (DMF) and water cont aining 0.1 mol dm(-3) (C2H5)(4)NClO4 and (C2H5)(4)NCl, respectively, a s constant ionic media at 25 degrees C. A very small heat of complexat ion other than the heat of dilution of titrant was evolved in the cour se of the titration of sodium, potassium, rubidium, cesium and ammoniu m ions with 12-crown-4 in water; thus, the complexation of 12-crown-4 with these cations is expected to be very weak. The formation of [M(12 -crown-4)](+) and [M(12-crown-4)(2)](+) (M=Na+, K+, Rb+, Cs+) complexe s was revealed in DMF, and their formation constants, reaction enthalp ies and entropies were determined. On the other hand, no significant h eat ascribable to complexation was liberated for the ammonium 12-crown -4 DMF solutions, and the formation of the ammonium 12-crown-4 complex was very weak, practically negligible. The cavity size of 12-crown-4 is 57 pm in radius, while the alkali-metal ion has an ionic radius of 116 - 181 pm. Since 12-crown-4 is too small to fully accommodate any a lkali-metal ion, the formation of the [M(12-crown-4)](+) and [M(12-cro wn-4)(2)](+) (M=Na+, K+, Rb+, Cs+) complexes results. The formation co nstants, enthalpies and entropies for the [M(12-crown-4)](+) (M=Na+, K +, Rb+, Cs+) complexes do not differ significantly by metal ions. Thus , in DMF, 12-crown-4 is not able to distinguish metal ions having diff erent sizes.