The effect of the change in substituents’ positions on the formation of supramolecular networks and the solvent type/substituent dependence of prototropic behavior in three new o-hydroxy Schiff bases

Abstract

The effect of substituent position on the formation of supramolecular topology, intra-molecular geometry and tautomeric behavior, and the dependence of prototropy on the solvent type have been investigated applying the XRD, UV–Vis, NMR, DFT, PES and HOMA methods on three new o-hydroxy Schiff bases. Based on key geometric parameters, total molecular energy and aromaticity calculations, the XRD, DFT and HOMA studies propose the phenol-imine structure as the most consistent tautomeric form for the compounds. PES and HOMA studies give results that relate the preference of the phenol-imine form to its high π-electron delocalization. For the solvent type dependence of tautomerism, the investigation of UV–Vis and NMR spectra and the PES studies for different solvent media reveals that the co-existence of two tautomeric structures becomes easier by increasing solvent polarity. As to the effect of substituent position on the supramolecular topology, XRD studies show that different substituent positions cause different types of non-covalent inter-molecular interactions in the crystal packings of the compounds. This is resulted in a significant change in the formation and topology of the supramolecular architecture, emphasizing the importance of a substituent position as a regulator in crystal engineering.