A new calix[4]arene-bis(crown ether) derivative displaying an improved caesium over sodium selectivity:: molecular dynamics and experimental investigation of alkali-metal ion complexation

In the light of computational studies suggesting enhanced cation-binding abilities for various benzo derivatives of calix[4]arene-bis-crown-6 macrocycles, the synthesis and properties of one of these ligands, BC6B2, have been investigated. In this compound, di(1,2-phenylene)-annelated glycolic chains link the 1,3- and 2,4-phenyl rings of the calixarene, thereby forcing it into the 1,3-alternate conformation. The detailed structures of BC6B2 . CH3NO2 1 and Cs-2(NO3)(2)BC6B2 . CHCl3. H2O 2 have been established by X-ray crystallography. Studies of coordination and solvent extract-ion of the alkali-metal ions have been used to compare this ligand with a number of related systems known previously.