Synthesis,characterization, crystal structure,and DNA-binding of ruthenium(II) complexes of heterocyclic nitrogen ligands resulting from a benzimidazole-based quinazoline derivative

The reaction of cis-RuCl₂(dmso)₄] with 6-(2-pyridinyl)-5,6-dihydrobenzimidazo1,2-c]quinazoline] (L) afforded in pure form a blue ruthenium(II) complex, Ru(L¹)₂] (1), where the original L changed to 2-(1H-benzoimidazol-2-yl)-phenyl]-pyridin-2-ylmethylene-amine (HL¹ ). Treatment of RuCl₃?·?3H₂O with L in dry tetrahydrofuran in inert atmosphere led to a green ruthenium(II) complex, trans-RuCl₂(L²)₂] (2), where L was oxidized in situ to the neutral species 6-pyridin-yl-benzo4,5]imidazo1,2-c]quinazoline (L² ). Complex 2 was also obtained from the reaction of RuCl₃?·?3H₂O with L² in dry ethanol. Complexes 1 and 2 have been characterized by physico-chemical and spectroscopic tools, and 1 has been structurally characterized by single-crystal X-ray crystallography. The electrochemical behavior of the complexes shows the Ru(III)/Ru(II) couple at different potentials with quasi-reversible voltammograms. The interaction of these complexes with calf thymus DNA by using absorption and emission spectral studies allowed determination of the binding constant K _b and the linear Stern–Volmer quenching constant K _SV.