(E)-2-[(2-hydroxybenzylidene)amino]phenylarsonic acid Schiff base: Synthesis, characterization and theoretical studies

• A new Schiff base enol tautomer by spectroscopic and theoretical studies.
• Intramolecular hydrogen bonds interactions NH⋯O in enol tautomer.
• The keto → enol tautomerization process was theoretically determined by DFT methods.

The structure of the Schiff base (E)-2-[(2-hydroxybenzylidene)amino]phenylarsonic [(E)-HBAPhAA], synthesized from salicylaldehyde and o-aminophenylarsonic acid in the presence of HCl, was characterized by FTIR, 1H NMR, EI-MS, UV–Vis spectroscopy, and X-ray crystallography. The crystal belonged to the monoclinic space group P21/c. Two molecules formed a dimer via intermolecular interactions due to the attachment of H atoms to O1, O3 and O4 with OH bond distances within reasonable ranges, ca. 0.84(3) Å. The structure also showed two intramolecular interactions of 2.634(2) and 3.053(2) Å for NH⋯O hydrogen bonds, which caused the structures to be almost planar. We performed a theoretical analysis using DFT theory at B3LYP/6-31+G(d,p) level to determine the stability of the E and Z conformers. The geometry analysis of the E- and Z-isomers revealed an interconversion energy barrier between E/Z isomers of 22.72 kcal mol−1. We also theoretically analyzed the keto form of the E-isomer and observed a small energy barrier for the tautomerization of 6.17 kcal mol−1.

The molecular structure of a new Schiff base containing the hydroxy OH and arsonic AsO(OH)2 moieties is completely characterized.Figure optionsDownload as PowerPoint slide