X-Ray crystallographic and spectroscopic properties of eight Schiff bases as evidence of the proton transfer reaction. Role of the intermolecular hydrogen bond

Abstract

A spectroscopic study of several ortho-hydroxy Schiff bases was carried out, and the corresponding crystal structures were analyzed in order to identify their characteristic hydrogen bonding patterns. The X-ray analysis showed that the enol (O–H⋯N) tautomer is the most stable in compounds 1–3 whereas the keto (N–H⋯O) form is preferred in compounds 4–7. The specific intermolecular O–H⋯O hydrogen bonding interactions that control the supramolecular arrangement of each tautomer are discussed. Additionally, a complete characterization of the polycrystalline samples was attained using solid-state NMR and IR experiments. Solution VT NMR and UV-visible experiments were also used to obtain valuable insights about the nature and stability of the tautomers.