Mononuclear Complexes Based on Pyrimidine Ring Azo Schiff-Base Ligand: Synthesis, Characterization, Antioxidant, Antibacterial, and Thermal Investigations

Six transition metal(II) complexes with the heterocyclic ligand HL (1), [CuL2]center dot H2O (2), [NiL2]center dot 3H(2)O (3), [CoL2]center dot 3H(2)O (4), [MnL2]center dot 3H(2)O (5), [ZnL2]center dot 2H(2)O (6), [PdLOAc]center dot H2O (7) [HL = 5-benzoyl-1-((E)-(2-hydroxy-5-((E)-phenyldiazenyl)benzylidene)amino)-4-phenylpyrimidin-2(1H)-one] were synthesized. The features of the azo Schiff bases were assigned from microanalytical, spectroscopic (IR, UV/Vis., H-1- and C-13 NMR, API-ES mass), magnetic, and molar conductivity measurements at room temperature as well as thermal analysis. The electronic absorption spectroscopy and magnetic susceptibility measurements of the complexes indicate square pyramidal arrangement for Pd-II and octahedral environment for all the other complexes. The azo Schiff base HL acts as a monobasic tridentate ligand, which commonly coordinates through the oxygen atoms of the phenol OH and the pyrimidine one group, and the nitrogen atom of the azomethine group. The thermal behaviors of the ligand and its metal complexes were studied using thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The metal complexes proved to be more thermally stable than the ligand; they decomposed at 10-30 degrees C higher temperatures. Antioxidant properties of the ligand and its metal complexes (DPPH free radical scavenging, ferrous chelating and reducing power activities) were tested. Antimicrobial activities were studied with gram-positive bacteria, which included Bacillus subtilis and Staphylococcus aureus, whereas Escherichia coli and Pseudomonas aeruginosa represented gram negative bacteria.