Syntheses, crystallography and spectroelectrochemical studies of ruthenium azomethine complexes

Three novel families of azomethine ligands L of the type C₆H₅N{double bond, long}NC(COCH₃){double bond, long}N(4-YC₆H₄) (6), C₆H₅N{double bond, long}NC(CO₂CH₃){double bond, long}N(4-YC₆H₄) (7) and 4-ClC₆H₄N{double bond, long}NC(CO₂CH₃){double bond, long}N(4-YC₆H₄) (8), [Y = H (a), CH₃ (b), Cl (c), Br (d), C₁₀H₇ (e), OCH₃ (f), NO₂ (g)] have been synthesized and reacted consecutively with RuCl₃, 2,2′-bipyridine (bpy) and lithium chloride in ethanol under refluxing conditions to produce three novel families of trans-[Ru^II(bpy)LCl₂] complexes. These complexes were characterized by elemental analysis, IR, ¹H NMR, UV-Vis spectroscopy and cyclic voltammetry. Crystallographic studies of two ruthenium(II) azomethine complexes (13 and 18) show that the Ru(II) ion occupies a distorted octahedral coordination sphere in which the chloride ligands are trans to each other and the azomethine and bipyridine nitrogen donor atoms are equatorially coordinated. Crystallographic, electrochemical, electronic spectral data and time-dependent DFT calculations are all consistent with azomethine ligands possessing strong π-acceptor properties. These π-acceptor properties can be "tuned" by a judicious choice of substituents on the azomethine ligand.