Structural comparisons of the binding cores formed by 1,3-di-Amide derivatives of p-tert-Butylcalix[4]arene: arms stabilization through Intra-molecular interactions including N-H***O, O-H***Cl and π***Cl types
Résumé
his paper deals with the development of a receptor with selectively functionalized at the lower rim of p-tert-butyl calix[4]arene linked through amide bond, resulting in the diamide derivatives (L 1 , L 2 and L 3 ) suitable for sensing ions and molecules. All the derivatives were thoroughly characterized by analytical and spectral methods. These derivatives were structurally characterized by single crystal X-ray diffraction and the conformational features of the calix[4]arene as well as the pendants are discussed. The L 1 and L 2 exhibited intramolecular hydrogen bond interaction between the N-H and the lower rim phenolic oxygen in addition to the circular hydrogen bonding between the phenolic O-H and the ether oxygen of the adjacent strand. The corresponding H-bond is absent when no 'H' is present on amide-N as in case of L 3 . Such intramolecular N-H***O interactions observed with the pendant results in a conformational bend responsible for the orientation of the arms and there by the nature of the binding core formed. Thus the binding cores formed differ largely between L 3 and the other two.