Dinuclear Zn(II) and tetranuclear Co(II) complexes of a tetradentate N2O2 Schiff base ligand: Synthesis, crystal structure, characterization, DFT studies, cytotoxicity evaluation, and catalytic activity toward benzyl alcohol oxidation

Two novel dinuclear Zn(II) and tetranuclear Co(II) complexes of a tetradentate N2O2 Schiff base ligand (H2L = N,N '-bis-(4-hydroxysalicylidene)-1,3-diaminopropane) were prepared. The structures of the H2L ligand, [4(Zn2L(mu-O2CCH3)(O2CCH3)(H2O))] . 4CH(3)OH . 3H(2)O (complex 1) and [Co4L2(mu-O2CCH3)(2)(O2CCH3)(2)].2H(2)O (complex 2) were unambiguously characterized by elemental analysis, mass spectrometry, Fourier-transform infrared spectroscopy (FT-IR), H-1 nuclear magnetic resonance (NMR), and UV-Vis spectroscopy. Single crystal X-ray diffraction studies revealed that two Zn(II) nuclei of 1 were connected through mu-phenolato and mu-acetato bridges and had distorted square pyramidal and distorted octahedral coordination geometries. Four Co(II) nuclei of 2, on the contrary, showed a Co4O4 cubane-like configuration in which Co(II) cations and O atoms were located at alternating corners of a distorted cube. Density functional theory studies at the B3LYP/6-31 G(d) level were carried out to gain an insight into the thermodynamic stability of the complexes. in vitro cytotoxicity of the ligand and the complexes were evaluated using the MTT assay against breast cancer MCF7 cells, melanoma cancer A375 cells, and prostate cancer PC3 cells as representative human cancer cell lines. Complex 1 showed a remarkable activity against A375 and PC3 cancer cell lines. In addition, 1 and 2 were used as precursors to produce zinc and cobalt oxide nanoparticles via pyrolysis technique. The resulting ZnO and Co3O4 nanoparticles were characterized using FT-IR spectroscopy, UV-Vis diffuse reflectance spectroscopy, powder X-ray diffraction, and field emission scanning electron microscopy. Then, these nanoparticles were used as heterogeneous catalysts in the oxidation of benzyl alcohol with hydrogen peroxide at room temperature. Both catalysts showed good recyclability with a negligible decrease in their efficiency during four catalytic cycles. The results of theoretical calculations showed that the most stable product was benzaldehyde, which is in good agreement with the obtained experimental results.