Synthesis, structural elucidation, Hirshfeld surface analysis and cytotoxicity studies of homometallic dinuclear Cu(II), Ni(II) and Zn(II) Schiff base complexes derived from m-phenylenediamine

Abstract

A polydentate Schiff base ligand, L was synthesized via condensation reaction between o-vanillin (OVan) and trimethyl-m-phenylenediamine [(Me)MPD]. Its Cu(II), Ni(II), and Zn(II) dinuclear complexes were prepared through complexation with corresponding acetate salts. The compounds were characterized via CHN elemental analyzer, molar conductivity, magnetic susceptibility, TGA, IR, 1H and 13C NMR. The crystal structure of the ligand, L and zinc(II) complex, Zn2L2 were elucidated by using single crystal x-ray diffraction. The crystal structure of Zn2L2 showed that the two Zn(II) metal atoms serve as bridges between the two units of the ligand through ONNO donor atoms leading to the formation of a centrosymmetric cyclic dinuclear complex. Based on the single x-ray crystallography, the zinc atoms exhibit a distorted tetrahedral geometry. Hirshfeld surface analysis was performed to determine the intermolecular interactions in the crystal structures. From this analysis, it revealed that H···H interaction for L (55%) and Zn2L2 (62.7%) was the dominant intermolecular interaction in the total area of Hirshfeld surface. The ν(CN) and ν(CO) peaks in IR spectra of the ligand L appeared at 1615 cm−1 and 1255 cm−1, respectively. The peaks shifted to lower and higher frequency by Δν of 4–12 cm−1 in the complexes. The new peaks assignable to ν(MN) and ν(MO) were observed at 514–562 cm−1 and 422–436 cm−1, respectively, indicating the coordination of the metal centers to the azomethine N and phenolic O. The Cu(II) and Ni(II) complexes are paramagnetic with μeff of 1.90 and 2.89 B.M., respectively. The thermal gravimetric analysis revealed the presence of three lattice water molecules in Cu(II) complex. The cytotoxicity studies of all compounds were carried out against colon cancer cell lines (HCT116). The parent ligand was found to be less cytotoxic than its metal complexes. Cu(II) showed the highest activity with IC50 of 0.73 ± 0.21 μM, better than the standard 5-FU.