Experimental and theoretical study of the first thiacalixcrowns and their alkali metal ion complexes

The synthesis, crystal structure and extraction properties towards Na+ and Cs+ of thiacalix[4]-bis(crown-n) (with n = 5 and 6) are reported. Experimen tal investigations show that both ligands as well as unsubstituted thiacali x[4]arene are less efficient than their calixarene counterparts for the ext raction of alkali metal ions. The structures and dynamic behavior of the hy pothetical alkali metal ion complexes have been investigated by molecular m odelling: the caesium. cation I is located close to the thiacalixarene cavi ty and does not interact strongly with the crown, which does not fulfil ful ly its role of ligand. The comparison of calixarene-crown with thiacalixare ne-crown confirms that the size of the calixarene cavity in the 1,3-alterna te conformation is a key parameter in the remarkable affinity of these mole cules for caesium.