A thiourea-functionalized benzo-15-crown-5 for cooperative binding of sodium ions and anions

A new bifunctional receptor 1 for cooperative complexation of cations and a nions is synthesized on the basis of benzo-15-crown-5, functionalized with a thiourea moiety as anion binding sites. When Na+ is bound to the crown mo iety of 1, the association constants of I-, Br- and NO3- in CD3CN are signi ficantly increased, as compared with free 1. Thermodynamic studies indicate that these large increases in complex stabilities can be ascribed primaril y to the enthalpic effect.