A macrobicyclic receptor with versatile recognition properties: Simultaneous binding of an ion pair and selective complexation of dimethylsulfoxide

A bicyclic receptor was synthesized and evaluated for its ability to bind alkali halide salts and polar neutral molecules in organic solvents. The receptor design is relatively straightforward in the sense that it is a combination of a dibenzo-18-crown-6 and a bridging 1,3-phenyldicarboxamide. In the presence of 1 mol equiv of metal cation, chloride affinities are enhanced in the order: K+ (9-fold enhancement) > Na+ (8-fold enhancement) much greater than Cs+ (no enhancement). An X-ray crystal structure shows that the receptor binds sodium chloride as a solvent-shared ion pair. The receptor has very weak affinity for acetonitrile, nitromethane, or acetone in chloroform solvent, whereas the association constant for dimethylsulfoxide is 160 M-1 at 295 K. An X-ray crystal structure shows that the dimethylsulfoxide is bound deeply in the receptor cavity and forms hydrogens bonds to the receptor via a bridging water molecule. There is also evidence for CH-O interactions. Solid-liquid extraction studies show that the receptor can dissolve and associate with urea, primary amides, and primary sulfonamides in CDCl3 but does not dissolve amino acids.