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Four novel aqua-bridged dinuclear complexes with a formula M2(mu-H2O)(mu-OAc)2(Im)4(OAc)2(Im)4(OAc)2 (where Im=imidazole, M=Mg2+ 1, Mn2+ 2, Ni2+ 3 and Co2+ 4) have been synthesized and characterized. Complexes 1, 2 and 3 have been characterized by X-ray crystallography. Two M2+ ions are bridged by an aqua molecule and two carboxylate anion with M...M=3.635-3.777 A, M-OH(2)=2.109-2.246 A and M-OH(2)-M=114.4-119.0 degrees, respectively. Each complex is further stabilized by two intramolecular hydrogen bonds between the hydrogens of the bridging aqua and the oxygens of the terminal monodentate acetates with a distance of O...O=2.6 A. The terminal monodentate acetates display "reversed" C-O distances, namely the C-O(free) distances are actually longer than the C-O(coordinating) distances. This abnormal geometry of a monodentate carboxylate would be caused by the strong "pulling effect" on the terminal carboxylates by intra- and intermolecular hydrogen bonds. The O-H stretching vibration of the bridging water was identified at ca. 2328 cm(-1) in IR spectra based on the deuterium isotope shift. The solid state 13C and 15N NMR spectra of 1 displayed two sets of peaks for acetate and Im ligands, respectively, consistent with the presence of two types of coordination modes of acetate and the two symmetrically non-equivalent Im as revealed by X-ray structure. 15N chemical shift of NH in Im ligands underwent about 6 ppm downfield shift due to its involvement in an intermolecular hydrogen bond.

Acenaphtheno[1,2-b]-1,4,8,9-tetraazatriphenylene (atatp) and its complexes [Ru(L)2atatp](ClO4)2 x nH2O (L = 2,2'-bipyridine (bpy), n=2 (1); 1,10-phenanthroline (phen), n=2 (2); and 2,9-dimethyl-1,10-phenanthroline (dmp), n=1 (3)) have been synthesized and characterized by elemental analyses and 1H NMR. The spectral and electrochemical properties of these complexes are also examined. Complexes 1 and 2 display bright luminescence in acetonitrile but very weak luminescence in water solution. However, complex 3 is not luminescent in either solvent. The interaction of the complexes with calf thymus DNA (CT-DNA) has been studied by absorption, emission and viscosity measurements. The intrinsic binding constants of complexes 1 and 2 are 7.6 x 10(4) and 8.8 x 10(4) M(-1) respectively. The relatively low affinities of complexes 1 and 2 with DNA may arise from the atatp ligand, indicating that the size and shape of the intercalated ligand have a marked effect on the strength of interaction. Complexes 1 and 2 bind with CT-DNA in an intercalative mode but complex 3 in a non-intercalative one, showing that changing the ancillary ligand affects not only the binding magnitude, but also the binding mode of the interaction.

Two structurally related ligands (L) 4,5,9,18-tetraazaphenanthreno[9,10-b] triphenylene (taptp) and 2,3-diphenyl-1,4,8,9-tetraazatriphenylene (dptatp), and their related complexes of [Ru(bpy)2L]2+ have been synthesized and characterized by elemental analyses, 1H NMR and mass spectra. Their electrochemical properties were also examined. Both complexes emit intense luminescence in organic solvent but are quenched in water to different extents. The interactions of the complexes with calf thymus DNA have been investigated by viscosity, absorption, emission and circular dichroism spectra. The intrinsic binding constants of [Ru(bpy)2(taptp)]2+ and [Ru(bpy)2(dptatp)]2+ are 1.7 x 10(5) and 3.8 x 10(4) M-1, respectively. All data indicate that both complexes bind enantioselectively to double-stranded calf thymus DNA via the intercalative mode, with stronger affinity for the fully planar ligand complex of [Ru(bpy)2(taptp)]2+.