Synthesis, characterization, DNA-binding properties and electronic structure (DFT) of ruthenium oligopyridine complexes

The complexes of the general formulae [Ru(terpy)(dcbpy)X]q (dcbpy = 4,4′-dicarboxy-2,2′-bipyridine; X = Cl−, 1; NO+, 2; image, 3; q = 1+, 3+ and 1−, respectively) have been synthesized and characterized. The DNA binding properties of structurally similar complexes [Ru(terpy)(dcbpy)NO2]−, 3, [Ru(terpy)(4-CO2-4′-Mebpy)NO2], 4, and [Ru(terpy)(bpy)NO2]+, 5, were studied, and their DNA affinities (Kb) were calculated as 6 ± 0.3 × 104 M−1, 8 ± 1.1 × 104 M−1 and 9.7 ± 0.02 × 106 M−1. The structural and spectroscopic properties of complexes 3–5 were investigated by DFT and TD DFT electronic structure calculations. The equilibrium geometries of complexes 3–5 in vacuum correspond to a distorted octahedral stereochemistry. The high-lying peaks of the absorption spectra of the complexes, ranging from 440 to 529 nm, are assigned to MLCT/LLCT transitions. These transitions are red-shifted upon adding carboxy substituents to the bipyridine ligand while the low-lying LLCT transitions, absorbing at 779 and 659 nm, are blue-shifted. Noteworthy is the excellent agreement of the TD DFT simulated absorption spectra in aqueous solution with the experimental ones.