Synthesis, characterization and anticancer activity of mono- and dinuclear Ni(II) and Co(II) complexes of a Schiff base derived from o-vanillin

A Schiff base ligand, 6,6'-dimethoxy-2,2'-[o-phenylenebis(nitrilomethylidyne)]diphenolato (LA), and its mononuclear and dinuclear Ni(II) and Co(II) complexes were synthesized. Structural elucidation was carried out via elemental analysis, molar conductivity, IR, NMR, UV-Vis spectroscopy, TGA and magnetic susceptibility. Single crystal X-ray diffraction of the Ni(LA) complex revealed a square planar geometry of the Ni(II) centre, with the ligand acting as a tetradentate ONNO chelate. Upon coordination to the metal centers, the nu(C=N) and nu(C-O) peaks shifted to lower frequencies, with appearance of new peaks assignable to nu(M-N) and nu(M-O) in the ranges 535-560 and 421-460 cm(-1), respectively. Ni(LA) and Ni-2(LA) complexes are diamagnetic, whereas the Co(LA) and Co-2(LA) complexes are paramagnetic with 3 unpaired electrons each. All the complexes displayed low molar conductivities in acetonitrile indicating non-electrolytic behavior. Anticancer screening against human colorectal cancer HCT116 cell lines revealed that both dinuclear complexes were more active than their mononuclear counterparts. Ni-2(LA) showed the highest potency with an IC50 value of 0.81 mu M. (C) 2019 Elsevier Ltd. All rights reserved.