Calix[4]arenes containing urea and crown/urea moieties: effects of the crown ether unit and Na+ towards anion binding ability

Calix[4]arenes containing urea and crown/urea moieties, 7 and 10, respectively have been synthesized. 1H NMR titrations of 7 and 10 with anions in DMSO-d6 showed that 7 and 10 formed complexes with Cl−, Br−, NO3− and H2PO4− to a different extent. The association constants of 7 and 10 towards anions were calculated and found to vary as H2PO4−>Cl−>Br−>NO3−. However, compared to 7 the presence of the crown unit in 10 resulted in a slightly higher affinity to Cl− and Br−, but a lower affinity to H2PO4−. Upon addition of Na+, the binding ability of 10 towards H2PO4− is increased due to ion-pair enhancement.