Synthesis, characterization and hydrogen bonding attributes of halogen bonded O-hydroxy Schiff bases: Crystal structure, Hirshfeld surface analysis and DFT studies

Abstract

Abstract Halogen bond has been the focus of crystal engineering for many decades. The role of intra molecular halogen bonds on adjacent intramolecular hydrogen bonding attributes has hardly been investigated. The O-hydroxy Schiff bases offer a good platform to shed light on these bonding aspects. The halogen bonded O-hydroxy Schiff bases were synthesized by the reaction of aldehydes with primary amines. Compounds were then characterized using mass, FTIR and NMR spectroscopic methods. Finally, the three dimensional molecular structures of all the Schiff base compounds were confirmed through single crystal X-ray diffraction studies. The crystal structures exhibit both inter and intramolecular hydrogen bond interactions. The O–H⋯N intramolecular interactions form the six membered pseudo chelate rings. The structures are also stabilized by C–O···π, N–O···π and π···π interactions. These molecular interactions were then quantified using Hirshfeld surface analysis. Further, the density functional theory calculations were employed using B3LYP hybrid functional with 6-311G+(d, p) level basis set to optimize the structural coordinates. The chemically active regions of the Schiff base molecules were identified by the analysis of molecular electrostatic potential surface.