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

Abstract

The reaction of cis-[RuCl₂(dmso)₄] with [6-(2-pyridinyl)-5,6-dihydrobenzimidazo[1,2-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-benzo[4,5]imidazo[1,2-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.

Keywords:

• Ruthenium(II) complexes
• Benzimidazole
• Quinazoline derivatives
• Crystal structure
• DNA-binding

Acknowledgments

Financial support from Department of Science and Technology, New Delhi, India is gratefully acknowledged. We thank EPSRC (UK) and the University of Reading for funds for the Image Plate.