CROWN-ETHER CONFORMATIONS IN 1,3-CALIX[4]ARENE BIS(CROWN ETHERS) - CRYSTAL-STRUCTURES OF A CESIUM COMPLEX AND SOLVENT ADDUCTS AND MOLECULAR-DYNAMICS SIMULATIONS

The crystal structures of solvent adducts of 1,3-calix[4]arene bis(18- crown-6) I and 1,3-calix[4]arene bis(naphtho-18-crown-6) 3 as well as the structure of the caesium complex of 3 have been determined. In 1.3 CH(3)NO(2) and 3.3CH(3)CN the complexed solvent molecules have their m ethyl group at the centre of the crown ether rings, whereas in 3.C6H5C H3, the solvent is located in the crystal voids. The consequences on t he crown ether conformations are noticeable: comparison with previous results shows that the conformation of I-is only slightly different in its acetonitrile and nitromethane adducts, the conformation with acet onitrile being the same as in the caesium and potassium complexes; the conformation of the acetonitrile adduct of 3 is the same as that in t he caesium complex and is strongly different from the one obtained by crystallization in toluene. Molecular dynamics simulations in vacua we re performed on free 3 and on its mononuclear caesium complex, and dis cussed in terms of the conformational mobility of the crown ether loop .