THERMODYNAMICS OF CALIX(4)ARENE ESTERS .1. COMPLEXATION OF ALKYL P-TERT-BUTYLCALIX(4)ARENETETRAETHANOATES AND ALKALI-METAL CATIONS IN ACETONITRILE AND IN BENZONITRILE

Using silver electrodes a double competition reaction involving crypta nds and calixarene esters has been for the first time used for the pot entiometric determination of stability constants of highly stable comp lexes of calixarene esters and metal cations (lithium and sodium) in a cetonitrile and in benzonitrile at 298.15 K. Corresponding data for le ss stable complexes were derived from thermochemical measurements usin g titration calorimetry (macro and micro). Thus, Gibbs energies, entha lpies, and entropies of complexation of alkyl (methyl, ethyl, and n-bu tyl) p-tert-butylcalix(Li)tetraethanoates and alkali-metal cations in acetonitrile and in benzonitrile at 298.15 K are reported. The results show that as the electron-donating effect of the ligand increases in moving from the methyl to the ethyl and to a lesser extent to the tert -butylcalix(4)arene ester, making the carbonyl oxygen more electronega tive, their interaction with metal cations increases. The implication of these finding on the selective recognition of alkali-metal cations by calix(4)arene esters in these solvents is discussed. It is conclude d that in both solvents (i) metal ion-ligand stability (hence Gibbs en ergy) is enthalpically controlled and (ii) entropies of calix(4)arenat e formation reflect marked differences between the solvation of the li gands relative to their metal-ion complexes.