Beschreibung:
<p>Two neutral macrobicyclic anion receptors 4 and 6, containing a calix[4]arene in the cone conformation, two L-alanine units, and a 2,6-diacylpyridine or a phthaloyl bridge, are described. The x-ray crystal structure of the acetone complexes of the pyridine containing macrocycle 6 shows the four amide NH groups to be in close proximity to the chiral pocket delimited by the pyridine and one aromatic nucleus of the calix[4]arene. This conformation is also the most stable in acetone-d6 solution, as proven by one- and two-dimensional NMR spectral measurements. Electrospray ionization-MS and <sup>1H</sup> NMR experiments reveal that the two ligands strongly bind carboxylate anions in acetone solution. H-bonding interactions between the carboxylate anions and the amide NH groups, together with π/π stacking, are invoked to explain the efficiency and the selectivity of these anion receptors.</p>