Ruthenium complexes incorporating azoimine and α-diamine based ligands: Synthesis, crystal structure, electrochemistry and DFT calculation

Ru(II) complexes, trans-[RuCl2(Azo)L] [where Azo = C6H5NNC(C6H5)NC6H5, L = 2,2′-bipyridine (bpy) (C1), 4,4′-dimethyl-2,2′-bipyridine (dmb) (C2), 1,10-phenanthroline (phen) (C3), 5-amino-1,10-phenanthroline (NH2phen) (C4)] were synthesized and characterized by spectroscopy (IR, UV–Vis, and NMR), cyclic voltammetry and crystallography. The new Azo ligand was isolated as amidrazones, H2Azo {where H2Azo is C6H5NHNC(C6H5)NHC6H5}, but oxidized to azoimines (Azo) during the formation of the Ru(II) complexes. A crystallographic analysis of C1 showed that the Ru-center is in a distorted octahedral coordination sphere in which the donor atoms around the Ru(II) center occupy cis:cis:trans N,N(Azo):N,N(bpy):Cl,Cl positions. The Ru(II) oxidation state is greatly stabilized by the novel Azo bidentate ligand showing Ru(III/II) oxidation couples ranging from 1.10 to 1.15 V. The absorption spectrum of C1 in acetonitrile was modeled by time-dependent density functional theory.