[en] Reaction of [(arene)MCl 2 ]2 with bidentate 4, 5-diazafluorene-9-one (dafo) and derived Schiff- base ligands (L1–L3) in the presence of ammonium hexafluorophosphate yielded mononuclear cationic complexes having general formula [(arene)MLCl]PF 6 {M = Ru, arene = benzene (1, 5, 9); M = Ru, arene = p- cymene (4, 8); M = Rh, arene = Cp* (2, 6, 10); M = Ir, arene = Cp* (3, 7, 11); L = 4, 5-diazafluorene-9-one (L1), N-(4, 5-diazafluoren-9-ylidene)aniline (L2), N-(4, 5-diazafluoren-9-ylidene)phenyl hydrazine (L3)}. All these complexes were isolated as hexafluorophosphate salts and characterized by spectral and analytical techniques such as FT-IR, UV-vis, NMR spectroscopy and ESI-Mass spectrometry. Complexes 1-3 were characterized by X-ray crystallographic studies, which indicated NN0 bidentate coordination of the ligands through pyridine nitrogen atoms of the ligand. To evaluate the biological properties of these complexes, antibacterial and antioxidant experiments have been carried out. The complexes 8, 9 and 11 exhibited antibacterial activity against Gram-positive bacteria. Results also show that the compounds possess prominent antioxidant activity against DPPH radicals. (author)