Thermodynamics of alkyl p-tert-butylcalix(4)arenetetraethanoates. 2. Solution studies of calix(4)arene esters and lithium and sodium ethylcalix(4)arene ester complexes: Coordination data in the solid state

Solubility data for ethyl p-tert-butylcalix(4)arenetetraethanoate and its sodium perchlorate complex in acetonitrile at 298.15 K are used to derive the standard solution Gibbs energies of these species in this solvent at 298.15 K. The thermochemical behavior of alkyl (methyl, ethyl, and n-butyl) p-tert-butylcalix(4)arene esters is discussed on the basis of ¹H NMR data in these solvents. Standard enthalpies of solution of the sodium and lithium perchlorate complexes of the tetraethyl ester derivative in acetonitrile and in benzonitrile at 298.15 K are first reported. A considerable change is observed in the enthalpic stability of the free ligand relative to its sodium perchlorate complex, in these solvents. From enthalpy data for the host, the guest, and the resulting complex the differences previously observed in the standard enthalpies of complexation of lithium and sodium with calix(4)arene esters in these solvents are explained. Combination of solution and previously reported complexation data leads for the first time in the area of calixarene chemistry to the calculation of the thermodynamic parameters associated with the coordination process referred to reactants and product in the solid state. The importance of these data is emphasized.