Crown ether conformations in 1,3-calix[4]arene bis(crown ethers): crystal structures of a caesium complex and solvent adducts and molecular dynamics simulations *

Abstract

The crystal structures of solvent adducts of 1,3-calix[4]arene bis(18-crown-6) 1 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 1·3CH3NO2 and 3·3CH3CN the complexed solvent molecules have their methyl group at the centre of the crown ether rings, whereas in 3·C6H5CH3, the solvent is located in the crystal voids. The consequences on the crown ether conformations are noticeable: comparison with previous results shows that the conformation of 1 is only slightly different in its acetonitrile and nitromethane adducts, the conformation with acetonitrile being the same as in the caesium and potassium complexes; the conformation of the acetonitrile adduct of 3 is the same as that in the caesium complex and is strongly different from the one obtained by crystallization in toluene. Molecular dynamics simulations in vacuo were performed on free 3 and on its mononuclear caesium complex, and discussed in terms of the conformational mobility of the crown ether loop.