Interaction of polypyridyl ruthenium(II) complexes containing non-planar ligands with DNA

2-(2-Chlorophenyl)imidazo[4, 5-f] 1,10-phenanthroline (CIP) or 2-(2-nitroph enyl)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 s ynthesized and characterized. The binding of the two complexes to calf thym us 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 bon ding mode for their parent compound, [Ru(bpy)(2)(PIP)](2+) (PIP = 2-phenyli midazo[4,5-f] 1,10-phenanthroline). The crystal structure of [Ru(bpy)(2)(CI P)]I-[ClO4](2). 2H(2)O was determined by X-ray diffraction analysis; the im idazo[4,5-f]1,10-phenanthroline moiety is not coplanar with the 2-chlorophe nyl ring, having a dihedral angle of 44.5 degrees in the CIP.