Several di-and tetrafunctionalized anion receptors have been synthesized by attaching 2,2,2-trifluoroethanol binding groups at the upper rim of cone calix[4]arenes using two different synthetic procedures. The best results were obtained hy treating calix[4]arene formyl derivatives with trifluoromelhyitrimethylsilane and tetra butyl ammonium fluoride in dry THF. The bistrifluoroethanol calix[4]arene receptors are able to bind anions showing selectivity for carboxylates and dihydrogenphosphate but at a lower efficiency compared to analogous receptors hearing urea, sulfonamide or activated amide binding groups. The conformational properties of the free ligands and their acelate complexes have heen investigated hy Dynamic 'H NMR, Molecular Modeling and in one case, by X-ray crystallography. CaHx[4|arenes bearing cation coordinating groups at the lower rim and 2,2,2-trifluoroethanol moieties at the upper rim behave as ditopic receptors, since they bind simultaneously cation and anion and extracts ion pairs in organic media. In one case evidence was obtained that coordination of sodium metal ion at the lower rim enhances the binding of acetate anion at the upper rim (positive allosteric effect).

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Calix[4]arenes in the 1,3-alternate conformation (1-3) and bearing activated amide groups at the upper rim have been synthesized and their anion binding properties studied and compared with conformationally mobile (4) or cone (Ib) receptors having the same binding groups. Association constants determined in CDCl3 show a stronger complexation for Y-shaped carboxylate anions and a higher efficiency for receptors (Ib and 3) bearing dichloroacetamido moieties as hydrogen bonding donor groups. Molecular modeling studies performed on the cone derivative (Ib) and its 1,3-alternate isomer (10) and ab initio calculations on 4-methoxyaniline derivatives (11-13) used as simplified models, reveal that the α,α-dichloroacetamido moieties bind anions in a bidentate fashion using both the N-H and the CHCl2 as hydrogen bonding donor groups. This explains the higher efficiency in carboxylate binding found for Ib and 3 that incorporate the dichloroacetamido binding unit in their structures.