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(d_π)→BL(π*) CT.

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