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

Abstract

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(μ‐O2CCH3)(O2CCH3)(H2O))]⋅4CH3OH⋅3H2O (complex 1) and [Co4L2(μ‐O2CCH3)2(O2CCH3)2]⋅2H2O (complex 2) were unambiguously characterized by elemental analysis, mass spectrometry, Fourier‐transform infrared spectroscopy (FT‐IR), 1H 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 μ‐phenolato and μ‐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.

Synthesis of Some Novel Nanosized Chelates of Anchoring Bisazo Dye 5-[5-(4,6-Dioxo-2-thioxo-hexahydro-pyrimidin-5-ylazo)-naphthalen-1-ylazo]-2-mercapto-1H-pyrimidine-4,6-dione and Their Applications as Antioxidant and Antitumor Agents

“…94 By that, the (H 4 L) ligand was more polarized, more reactive, and less kinetically stable by comparison with metal complexes. 95 This supported the experimental data (TGA) that confirmed the stability of complexes rather than the ligand. Hardness, softness, electronegativity, and chemical potential have been estimated as global reactivity descriptors for the examined metal chelates and neutral ligands.…”

“…Low energy gap values can also be attributed to the groups that conjugate . By that, the (H 4 L) ligand was more polarized, more reactive, and less kinetically stable by comparison with metal complexes . This supported the experimental data (TGA) that confirmed the stability of complexes rather than the ligand.…”

“…The hardness and softness of a molecule are vital in determining its stability and reactivity . The hard molecule has a large energy gap, whereas the soft molecule has a smaller one . The investigated (H 4 L) ligand can be considered as a soft molecule and the complexes are hard molecules.…”

“…96 The hard molecule has a large energy gap, whereas the soft molecule has a smaller one. 95 The investigated (H 4 L) ligand can be considered as a soft molecule and the complexes are hard molecules. The molecules with the lowest global hardness values should be more reactive than the others, reflecting that the ligand was more reactive.…”

In Situ Assembled Polynuclear Zinc Oxo Clusters Using Modified Schiff Bases as Ligands

“… 9 In this backdrop, Schiff-base ligands have been used for synthesizing zinc-based multinuclear clusters, some of which have shown interesting applications as polymerization catalysts, 10 reagents in organic synthesis, 11 molecular precursors for ZnO-based materials, 12 models of the active site in zinc enzymes, 13 and in synthesizing functional molecule-based materials. 14 Some of the molecular clusters of zinc reported in the literature are mononuclear, 15 binuclear, 16 trinuclear, 17 tetranuclear, 18 and polynuclear clusters. 19 Some of these structural forms, like the tetranuclear core cluster, have garnered special attention, particularly the manganese-based tetranuclear clusters, which have been involved in multielectron-transfer redox reactions of oxygen-evolving complex (OEC) of PSII in green plants.…”