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

Abstract

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- d 6 showed that 7 and 10 formed complexes with Cl −, Br −, NO 3 − and H 2PO 4 − to a different extent. The association constants of 7 and 10 towards anions were calculated and found to vary as H 2PO 4 −>Cl −>Br −>NO 3 −. 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 H 2PO 4 −. Upon addition of Na +, the binding ability of 10 towards H 2PO 4 − is increased due to ion-pair enhancement.