Selective colorimetric sensing of nickel (II) ions using 2-hydroxy-5-nitrobenzaldehyde-4-hydroxybenzoylhydrazone ligand: Spectroscopic and DFT insights

The abnormal levels of nickel (II) ions in body fluids have been linked to various ailments, and their ubiquitous environmental occurrence could pose a potential hazard. Hence, there is a pressing need to develop selective and miniaturized analytical techniques to efficiently monitor the level of nickel (II). In the present study, 2-hydroxy-5-nitrobenzaldehyde-4-hydroxybenzoylhydrazone (HNHBH) was synthesized and investigated as a potential colorimetric sensor for nickel (II) ions. A distinct color change was observed due to complex formation between HNHBH and nickel (II) ions. Both the free ligand and resulting complexes were characterized by UV-Vis, infrared and 1H NMR spectroscopies. A theoretical DFT method has been implemented to understand the nature of complexation based on the calculated binding energies and frontier molecular orbitals. The computational approach used predicts that HNHBH adopts an imidic acid tautomeric form when it coordinates with the metal ion center. The selectivity of HNHBH towards nickel ions was evaluated by taking into account a number of factors, such as solvent, pH and EDTA effects.