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.