Non-innocent behavior of 1-(2′-pyridylazo)-2-naphtholate coordinated to polypyridine ruthenium(II) complexes

The study of non-innocent redox behavior of ligands is important for the development of new catalysts and to comprehend the function of bioinorganic molecules in biochemical processes. In this work, we present a description of the non-innocent behavior of 1-(2'-pyridylazo)-2-naphtholate (pan) coordinated to ruthenium complexes. The synthesis and characterization of a series of [Ru(pan) (PPh3)(L)]PF6 complexes [where L = 2,2'-bipyridine (bpy), 4,4'-dimethyl-2,2'-bipyridine (dmbpy), and 1,10-phenanthroline (phen)] are presented. UV-vis analyses of the studied ruthenium complexes show intense absorptions from intraligand pi-pi* and metal-to-ligand charge-transfer transitions bands in the visible region. This observation shows a significant contribution of the pan ligand in all electronic transitions and is the indicative of non-innocent behavior. Theoretical calculations were carried out to support the UV-vis spectral assignments. Non-innocent behavior of pan was observed and confirmed using the electrochemical parameter E-L(L) and by electrochemical studies. The pan ligand is non-innocent and can be modulated by donor and acceptor character of the other ligands present in the coordination sphere of the complex.