Cobalt(II) complexes containing mefenamic acid with imidazole and pyridine based auxiliary ligands: Synthesis, structural investigation and cytotoxic evaluation

Abstract

The interaction between CoCl2.6H2O and mefenamic acid (2-[(2,3-dimethylphenyl)amino]benzoic acid) in the presence of imidazole and pyridine based ligands resulted in the formation of [Co(mef)2(imi)2]; C-1, [Co(mef)2(nic)2(H2O)2].2H2O; C-2, [Co2(µ-H2O)(µ-mef-O,O')2(mef)2(py)4].CH3CN; C-3, and [Co2(µ-mef-O,O')4(apy)2].2CH3CN; C-4, (mef is monodentate mefenamato, µ-H2O is bridging aqua ligand, µ-mef-O, O' is bridging bidentate mefenamato, imi is imidazole, nic is nicotinamide, py is pyridine, and apy is 2-aminopyridine). The complexes were characterized spectroscopically and by physicochemical properties. Single-crystal X-ray diffraction studies confirmed the structures of the complexes. In C-1, Co(II) is in four-coordinate geometry, while in C-2, Co(II) is in hexa-coordination with two mefenamato carboxylate oxygen atoms, two nitrogen atoms, and two oxygen atoms from two solvent ligands. Complex C-3 consists of two cobalt centers linked by an aqua ligand and bridged by two mefenamato ligands. Furthermore, the octahedral geometry in each Co(II) in C-3 was completed by coordinating two monodentate mefenamato ligands and monodentate pyridine ligands. Similarly, in C-4, a Co-Co bond connects two Co(II) centers in six-coordinate geometry, with four bidentate mefenamato ligands acting as bridges between the two Co(II) and two 2-aminopyridine nitrogen, in monodentate coordination to each Co(II). The lattice solvents in C-2 to C-4 participated in intermolecular hydrogen bonding interactions with the mefenamato ligand. FTIR studies showed the presence of both monodentate and bidentate coordination of the deprotonated carboxylate oxygen atoms of the mefenamato ligand, as well as the coordination of the nitrogen donor ligands in the complexes. TG analysis determined the complexes' thermal stability and decomposition steps and ascertained their compositions, which agreed with the analytical and X-ray crystallography studies. Furthermore, the cytotoxicity of mefenamic acid and the cobalt (II) complexes on lung carcinoma cells (NCIH-460) and breast cells (MDAMB) were assessed using MTT assay. The complexes showed higher cytotoxicity than mefenamic acid against the MDAMB cell line.