X-RAY-DIFFRACTION STUDIES AND SOLUTION THERMODYNAMICS OF 5,26,27,28-TETRA(DIETHYLAMINE)ETHOXY-CALIX(4)ARENE

The crystal structure of 23-para-tert-butyl-25,26,27,28-tetra(diethyla mine) ethoxycalix(4)arene has been determined from X-ray diffraction d ata. The substance crystallises in the space group P2(1)/a with a = 14 .103(2), b = 34.250(5), c = 14.486(2) Angstrom, beta = 105.15(1)degree s and Z = 4. The macrocycle consists of two distorted conical parts, o ne hydrophobic the other hydrophilic, linked through their smaller rim s. The larger bore of the hydrophobic cavity has transversal dimension s of about 5.90 x 5.90 Angstrom while the hydrophilic cavity reaches a pertures of 5.06 x 10.39 Angstrom at the aminoethyl nitrogen atom posi tions. The solubility of this ligand at several temperatures in variou s solvents has been determined and the data were used to derive its so lution Gibbs energies in these solvents at 288.15, 298.15 and 313.15 K . The enthalpy of solution for this calix(4)arene derivative in five s olvents was measured calorimetrically at 298.15 K. Thermodynamic param eters of transfer are calculated using benzonitrile as the reference s olvent. It is shown that the transfer Gibbs energy among these solvent s is almost 0 kJ mol(-1) as a result of an enthalpy-entropy compensati on effect, where the most significant enthalpic and entropic changes a re found in transfers to protic solvents.