Calix[5]crown-3-based heteroditopic receptors for n-butylammonium halides

(1,3)-Calix[5]arene-crown-3 derivatives 1a and 1b, bearing either three n-butylureido or 1-naphthylureido moieties at the lower rim, respectively, have been synthesised. Their cationic and anionic binding domains have been investigated by a combination of 1D- and 2D-NMR, UV/vis absorption and fluorescence and ESIMS techniques. Complexation data show that the attachment of 1-naphthyl groups at the lower rim of calix[5]crown-3 1b dramatically increases its anion-binding ability over the n-butyl-bearing derivative 1a. Overall, both 1a and 1b act as highly efficient heteroditopic receptors for n-butylammonium halides and in so doing bind these salt species—as spatially-separated ions—much more effectively than the single ionic components. The X-ray crystal structure of the pivotal tris-[2-(2-chloroethoxy)ethoxy]-calixcrown precursor 2 is also reported.