Experimental and theoretical evidence of the bidentate binding mode of dichloroacetamido groups at the upper rim of calix[4]arene hydrogen-bonding anion receptors

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 CDCl(3) 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 alpha,alpha-dichloroacetamido moieties bind anions in a bidentate fashion using both the N-H and the CHCl(2) 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.