The absolute necessity to fight some class of tumor is perceived as serious health concerns, so the discovery and development of effective anticancer agents are urgently needed. (E)‐4‐((2‐hydroxyphenyl)diazenyl)‐3‐phenyl‐1H‐pyrazol‐5(4H)‐one, HL, and its Ni(II), Pd(II) and Pt(II) complexes were synthesized and the biological activity was evaluated for antitumor, antioxidant and antimicrobial activity as well as DNA cleavage. Their structures were assigned depending on the elemental analysis, conductivity, magnetic moment, spectral measurements (IR, 1HNMR, mass and UV–Vis) and thermal analysis. 3D molecular modeling using DFT method confirmed that the geometrical structures agree well with the suggested experimental ones. The antitumor activity was evaluated against four different cell lines using MTT assay. The ligand HL showed a potent cytotoxic activity compared to 5‐fluorouracil as a reference drug. For metal complexes, the order of activity was: Pd(II) > Ni(II) > Pt(II). A remarkable antioxidant activity for the ligand HL was recorded. It was higher than that of the metal complexes. Results of antimicrobial experiments revealed that all compounds were moderate to highly active against selected bacterial strains but inactive as antifungal except Pd(II) which showed a moderate antifungal activity. Gel electrophoresis showed insignificant nucleases activity for the ligand or its metal complexes even in the presence of H2O2 providing protection of DNA from damage. The antitumor activity of our compounds may be not due to DNA cleavage but may be referred to a mechanism similar to that of 5‐fluorouracil which interfere with DNA replication. The present work suggests the use of this ligand in the design and development of new anticancer drugs.

This work describes the synthesis of a novel multiple dentation azo-Schiff base dye 2- ((3-((5-chlorobenzo[d]oxazol-2-yl)diazenyl)-4-hydroxybenzylidene) amino)pyridin-3-ol (H 2 L) based mixed heterocyclic bnzoxazole and pyridine moieties in facile two successive steps approach. Firstly is the synthesis of start azo dye 3- ((5-chlorobenzo[d]oxazol-2-yl)diazenyl)-4-hydroxybenzaldehyde (CBOAHB) followed by condensation with 3-hydroxy 2-amino pyridine. It's novel binuclear Ni (II), Cu (II), Ru (III), and Zr (IV) 2:1 metal-to-ligand stoichiometric complexes were synthesized and characterized via various spectroscopic and analytical techniques. The data showed the paramagnetic Ni 2+ complex has tetrahedral geometry, while the Cu 2+ , Ru 3+ , and diamagnetic Zr 4+ complexes have octahedral geometrical structures. Data of the crystallinity, morphology, and average particle size showed that Cu 2+ and Ru 3+ complexes were formed at the nanoscale. The geometrical structures according to 3D molecular modeling are in good agreement with those proposed by the experiments. The azo start CBOAHB, H 2 L, and its metal complexes have been examined for their biological and catalytic features. The Zr 4+ complex manifested higher antibacterial activity against Staphylococcus aureus (S. aureus), the ligand H 2 L exhibited higher antibacterial activity against Escherichia coli (E. coli), and the Ni 2+ complex showed higher antifungal activity against Candida albicans (C. Albicans). The anticancer activity was evaluated against human hepatocellular carcinoma (HepG-2), colorectal carcinoma (HCT-116), and human breast carcinoma (MCF-7). The ligand H 2 L has very strong cytotoxicity toward HepG-2 cells, Ni (II) complex has the strongest cytotoxicity against HCT-116 cells and Zr (VI) has the strongest cytotoxicity against MCF-7 cells. The findings of antioxidant activity are in perfect accord with those obtained from anticancer. The heterogeneous catalytic activity was examined for the reduction of Direct Blue 14 dye. Ru (III) complex and Cu (II) complex achieved the highest catalytic activity with the highest degradation % and within a very short time did not exceed 3 min.