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A novel asymmetric ligand 3-(pyrazin-2-yl)-as-triazino[5,6-f ]1,10-phenanthroline (pztp) and its mono- and bi-nuclear complexes [Ru(bpy)2(pztp)]2+ 1 and [(bpy)2Ru(pztp)Ru(bpy)2]4+ 2 (bpy = 2,2′-bipyridine) have been synthesized and characterized by UV/VIS, IR, 1H NMR and mass spectra. The electrochemical behaviours of complexes 1 and 2 were observed and displayed oxidation potentials at 1.37 and 1.39 and 1.60 V vs. saturated calomel electrode, respectively. The binding of the two complexes with calf thymus DNA has also been investigated by a spectrophotometric method and viscosity measurements. The results indicated that the two complexes interact with DNA in sharply different ways. The mononuclear complex 1 intercalates into DNA base pairs despite its small hypochromicity value, while the binuclear complex 2 binds to DNA via electrostatic interaction. The circular dichroism signals of the dialysates of the racemic complexes against calf thymus DNA are discussed.

2-(2-Chlorophenyl)imidazo[4,5-f]1,10-phenanthroline (CIP) or 2-(2-nitrophenyl)imidazo[4,5-f]1,10-phenanthroline (NIP) and their complexes [Ru(bpy)2(CIP)]2+ and [Ru(bpy)2(NIP)]2+ (bpy = 2,2′-bipyridine) have been synthesized and characterized. The binding of the two complexes to calf thymus DNA has been investigated with spectrophotometric methods and viscosity measurements. The experimental results indicate that the two complexes bind to DNA through a partial intercalative mode that is different from the bonding mode for their parent compound, [Ru(bpy)2(PIP)]2+ (PIP = 2-phenylimidazo[4,5-f]1,10-phenanthroline). The crystal structure of [Ru(bpy)2(CIP)][ClO4]2·2H2O was determined by X-ray diffraction analysis; the imidazo[4,5-f]1,10-phenanthroline moiety is not coplanar with the 2-chlorophenyl ring, having a dihedral angle of 44.5° in the CIP.