Structure, spectroscopic and electrochemical properties of novel binuclear ruthenium(II) copper(I) complexes with polypyridyl bridging ligands†
Abstract
Binuclear complexes of the type [(bpy)2Ru(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 (dpqMe2), 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 dm3 mol–1. Single crystal structures for [(bpy)2Ru(dpp)Cu(PPh3)2]3+ and [(bpy)2Ru(dpqMe2)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 π* 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(dπ)→BL(π*) CT.