Structure, spectroscopic and electrochemical properties of novel binuclear ruthenium(II) copper(I) complexes with polypyridyl bridging ligands

Binuclear complexes of the type [(bpy)(2)Ru(BL)Cu(PPh3)(2)](3+), where bpy = 2,2'-bipyridine, BL = 2,3-di-2-pyridylpyrazine (dpp), 2,3-di-2-pyridylquinoxaline (dpq), or 6,7-dimethyl-2,3-di-2-pyridylquinoxaline (dpqMe(2)), were readily formed by the reaction of [Cu(PPh3)(4)](+) with mononuclear complexes [Ru(bpy)(2)(BL)](2+). The binuclear complexes are stable in CH2Cl2 solution at concentrations above 10(-3) mol dm(-3) having equilibrium constants for formation in the range 1000-2500 dm(3) mol(-1). Single crystal structures for [(bpy)(2)Ru(dpp)Cu(PPh3)(2)](3+) and [(bpy)(2)Ru(dpqMe(2))Cu(PPh3)(2)](3+) show distortions of the bridging ligand in the form of twisting and splaying of the ring systems. Electrochemical and UV/Visible data suggest the {Cu(PPh3)(2)}(+) moiety has little affect in stabilising the BL pi* orbital. Resonance Raman spectra show the bichromophoric nature of the visible absorptions of the heteroleptic complexes; both bpy and BL ligand vibrations are enhanced depending on the excitation wavelength. Observation of a Ru-N vibration suggests that the dominant transition in the visible region is Ru(d(pi))--> BL(pi*) CT.