A novel series of mixed-ligand complexes of 5,5 0-{(1E,1E 0)-1,4-phenelynebis (diazene-2,1-diyl)}bis(quinolin-8-ol) (H 2 L 1) as a primary ligand and 4-aminoantipyrine(L 2) as a secondary ligand with Mn(II) ion were prepared using two general formulae: [Mn 2 (H 2 L 1) 2 (L 2) 2 X 4 ].4Cl (X = OH 2 (1), ONO 2 − (2), Cl=nil; OAc(3), Cl = nil) and [Mn 2 (H 2 L 1)(L 2) 2 (O 2 SO 2) 2 ](4). Free ligands and their complexes were characterized. Electronic absorption spectra of the mixed-ligand complexes indicate a distorted octahedral geometry around the central metal ion, and the anions X − are in the axial positions for all compounds. The ligands behave in a neutral bidentate manner, through nitrogen atoms and oxygen atoms of the carbonyl group (L 2), whereas H 2 L 1 coordinated through nitrogen and OH groups as a neutral bidentate ligand. All complexes do not contain coordinated water molecules, but complex (1) contains four water molecules. The water molecules are removed in a single step. The complexes exhibited magnetic susceptibility corresponding to five unpaired electrons. The antimicrobial activity of the Mn(II) mixed-ligand complexes (1-4) against two gram-positive bacteria, three local gram-negative bacteria, and three fungi species was tested. Mn(II) mixed-ligand complex (2) exhibited significant antibacterial activity against Bacillus cereus, Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas sp. Mixed-ligand complex (2) exhibited a high potential cytotoxicity against the growth of human lung cancer cells. K E Y W O R D S antimicrobial activity, azo compound, bacterial ultrastructure, 4-aminoantipyrine, ligand field parameters, mixed-ligand 1 | INTRODUCTION Pyrazole derivatives are important classes of compounds in organic chemistry. Many of them possess antimicrobial, antifungal, anti-inflammatory, and anticancerous properties. One of the important pyrazole derivatives is 4-aminoantipyrine whose structural units play a vital role in medicine and agricultural chemistry. [1-3] 4-Aminoantipyrine and its complexes have a variety of applications in analytical, biological, and pharmacological fields. [1] In the past few years, chemists have shown much interest in the synthesis and physicochemical study of row transition metal complexes with a number of azo dye ligands. [4-6] Azo dyes readily form stable complexes
