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. Experimental investigations show that both ligands as well as unsubstituted thiacalix[4]arene are less efficient than their calixarene counterparts for the extraction of alkali metal ions. The structures and dynamic behavior of the hypothetical alkali metal ion complexes have been investigated by molecular modelling: the caesium cation is located close to the thiacalixarene cavity and does not interact strongly with the crown, which does not fulfil fully its role of ligand. The comparison of calixarene–crown with thiacalixarene–crown confirms that the size of the calixarene cavity in the 1,3-alternate conformation is a key parameter in the remarkable affinity of these molecules for caesium.