Reaction of ZnCl2 and HgCl2 metal salts with a bidentate Schiff base ligand in methanol solution, X-ray crystal structure, and theoretical studies

From the reaction of ZnCl₂ and HgCl₂ metal salts with (E)-4-chloro-N-(pyridine-2-ylmethylene)benzeneamine (L) in methanol solution, two binuclear Schiff base complexes were prepared. Both complexes were characterized by elemental analysis, UV–Vis, and IR spectrophotometry. X-ray crystal structure analysis showed that metal ion in the resulting centrosymmetric dinuclear ML₂Cl₄ complexes is in a distorted trigonal bipyramidal and a distorted square pyramidal coordination environment in the case of Zn(II) and Hg(II) metal ions, respectively. Three types of reaction between MCl₂ salts and ligand L producing three different types of products—ML₂ ²⁺, MLCl₂, and M₂L₂Cl₄—were simulated in both the gas phase and solution. The gas phase calculations at DFT (B3LYP) level of theory using SDD, CEP-121G, and LanL2DZ basis sets showed that the binuclear M₂L₂Cl₄ complexes are more stable than corresponding mononuclear MLCl₂ complexes. Furthermore, both the gas phase and solution studies showed that the formation of M₂L₂Cl₄ complexes from the metal cations, chloride anion, and ligand molecule is energetically more favored than that of MLCl₂ and ML₂ ²⁺ complexes.