Calorimetric investigation of the complexation of didodecylcalix[4]arene-crown-6 with alkali metal and ammonium cations in acetonitrile

The Cs+ selectivity of some calix-crown ligands makes them excellent candid ates for use in separation systems such as liquid membranes. Separation per formance can be understood and predicted from thermodynamic data for cation complexation. We have therefore determined the log K, DeltaH and DeltaS fo r the interaction of Na+, K+, Rb+, Cs+ and NH4+ with didodecyl-calix[4]aren e-crown-6 in acetonitrile at 25 degreesC by titration calorimetry. The liga nd is strongly selective for Cs+, and the selectivity trend results entirel y from the enthalpy contribution, with entropy effects opposing the trend. These results are discussed in light of some corresponding data obtained by other researchers with similar ligands.