Structural features of nickel(II) mixed ligand complexes with mefenamic acid and nitrogen donor ligands

Abstract

The reaction between Ni(NO3)2.6H2O and the non-steroidal anti-inflammatory mefenamic acid (2-[(2,3-dimethylphenyl)amino]benzoic acid), in the presence of various nitrogen donor ligands (imidazole, 2-methylimidazole, pyridine, and nicotinamide) have resulted in the formation of four novel mixed ligand mononuclear Ni(II) complexes. A direct one step metal-ligand complexation method was adopted in synthesizing the complexes under similar conditions using a solvent mixture of EtOH: H2O (2:1). The synthesized complexes have the general formula; [Ni(mef)2(L)2(EtOH)2] or [Ni(mef)2(L)2(H2O)2]·2H2O, where mef is mefenamato, L is the corresponding nitrogen donor ligand. The complexes were characterized by analytical and spectroscopic methods. FTIR studies supported the complex formation and indicated that the mefenamato ligand was coordinated as monodentate through the deprotonated carboxylate oxygen atom. Single-crystal X-ray diffraction studies show that all the complexes crystallize in the triclinic space group P-1. The complexes are isostructural, and Ni(II) lies in an octahedral geometry with NiN2O4 chromophore. Parallel stacking arrangement of the ligands, similar intramolecular N-H···O, and intermolecular O-H···O interactions between the mefenamato ligand and coordinated solvent dominated the connectivity pattern in the complexes. Also, intermolecular interactions depending on the coordinated nitrogen donor ligand further stabilized the structures of the complexes. Furthermore, density functional theory (DFT) study was done to obtain the Hirshfeld charges on different atoms.