A novel azo-azomethine benzoxazole-based ligand and its transition metal (II), (III), (IV) complexes: Synthesis, characterization, theoretical studies, biological evaluation, and catalytic application

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 (H2L) 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 Ni2+ complex has tetrahedral geometry, while the Cu2+, Ru3+, and diamagnetic Zr4+ complexes have octahedral geometrical structures. Data of the crystallinity, morphology, and average particle size showed that Cu2+ and Ru3+ 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, H2L, and its metal complexes have been examined for their biological and catalytic features. The Zr4+ complex manifested higher antibacterial activity against Staphylococcus aureus (S. aureus), the ligand H2L exhibited higher antibacterial activity against Escherichia coli (E. coli), and the Ni2+ 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 H2L 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.