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

Abstract

This 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 (L₁, L₂ and L₃) 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 L₁ and L₂ 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 L₃. 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 L₃ and the other two.