Anion specificity induced conformational changes in cresol-based tripodal podands controlled by weak interactions: structural and Hirshfeld surface analysis

Abstract

N-bridged tripodal receptors have shown a distinct behaviour on their assembly and binding ability towards complexation with inorganic and organic anions. All supramolecular complexes have been structurally authenticated using X-ray diffraction with a detailed analysis of the Hirshfeld surfaces facilitating an understanding of the type and nature of intermolecular interactions present in the complexes and extended structures. The p-substituted podand (L₁1) crystallized in the symmetric rhombohedral R3c space group to form hemicarcerand in the solid state via intermolecular C–H⋯π interactions. Protonation of L_1–31–3 in presence of inorganic anions results in conformational locking of tripodal cavity by N–H⋯O_ether trifurcated hydrogen bond formation (1–4) due to the endo-orientation of the bridgehead hydrogen whereas use of organic anions as template leads to the exo-orientation of the apical proton (5–7) and thereby, results into conformational opening of the tripodal arms via the formation of N–H⋯O_anion and π⋯π interactions with the anion. This study also establishes bilayer assembly formation in inorganic anion complexes (2–4) guided primarily by interligand C–H⋯π interactions and multiple C–H⋯anion hydrogen bonds. NMR studies further establish the different orientations of flexible tripodal arms in presence of organic and inorganic counter anions in solution.