Two Schiff base tetradentate ligands 4 and 5 were synthesized by condensation reactions of 4-hydroxy-3-methoxy-5-((2-nitrophenyl)diazenyl) benzaldehyde 1 with 1,2-diaminoethane 2 and 1,2-diaminobenzene 3, respectively. Treatment of synthesized ligands with the manganese (II) chloride MnCl2 6 gave two complexes 7 and 8 of general formula ML. The synthesized ligands and their complexes were characterized by FTIR, UV-Vis, Mass spectroscopy, and elemental analysis. The biological activity of the synthesized compounds were tested. It was found that ligand 5 and the complexes 7 and 8 possess antibacterial activity against the gram –ve Proteus mirabilis.

In this study, the computerized molecular docking method was used to investigate the interactions of five nitro diazo dye derivatives 1-5 with COVID-19, CLpro, RAF and PLpro as very important viral proteins to target the coronavirus SARS-CoV-2. Among the used diazo dyes, compound 5 showed the highest binding free energies and the lowest inhibition constants Ki with all studied proteins, and it exhibits a large effect to inhibit the activities of the RAF and COVID-19. Therefore, compound 5 may be useful as an antiviral candidate that worth more trials for COVID-19 disease. The binding sites of compound 5 with the tested viral proteins were evaluated.

Two bis-Schiff Bases 1 and 2 are ligands that can coordinate with manganese metal to form stable complexes and have biological activity. Thermodynamic parameters, HOMO-LUMO energy levels and FTIR spectra of two ligands have been computed using B3LYP/6-311++G(d,p) functional of the DFT calculations. Both ligands are favored thermodynamically, and the ligand 1 has been shown to be more stable than ligand 2. The Polarizability values of two ligands have been investigated. The results refer that ligand 2 interacts earlier than ligand 1 to the metal ion. The FTIR spectra of two ligands have been evaluated. All results show the good agreement between the theoretical and experimental data.