Synthesis, crystal structure, spectroscopic investigations, and computational studies of Ni(II) and Pd(II) complexes with asymmetric tetradentate NOON Schiff base ligand

In the present study, an asymmetric tetradentate NOON Schiff base ligand 2,2′-((4-methyl-1,2-phenylene)bis(nitrilomethylylidene))bis(4-chlorophenol) (H2L) was synthesized by condensation of 4-methylphenylenediamine with 5-chlorosalicylaldehyde. The Ni(II) and Pd(II) Schiff base complexes were synthesized from the reaction of Ni(OAc)2·4H2O and Pd(OAc)2 with the Schiff base ligand (H2L) in methanol and acetonitrile, respectively. The ligand and its complexes were characterized by FT-IR, 1H NMR, UV-Vis spectroscopy, and elemental analyses. Moreover, the crystal structure of the ligand and Pd(II) complex has been determined by single-crystal X-ray crystallography. The single-crystal X-ray analysis of PdL complex demonstrated a four-coordinated complex by two nitrogen atoms and two phenolate groups. In addition, DFT and TD-DFT calculations were done using M06-2X and B3LYP levels of theory along with Def2-TZVP and ATZP basis sets for ligand and its complexes. Theoretical IR and nature of electronic transition in TD-TDFT data were analyzed by frequency and NBO-CMO calculations.