Mutual effects on the spectroscopic and electrochemical properties of μ3-oxo-trinuclear ruthenium complexes modified with a bridged [Ru(2,2′-bipy)2(CN)] moiety

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Abstract
The asymmetric dimers [Ru3O(CH3COO)6(py)2(B)Ru(2,2′-bipy)2(L)](PF6)2, where B = 4,4′-bipy or bpa (1,2-bis(4-pyridyl)ethane) and L = Cl− or CN−, have been characterised based on spectroscopic and electrochemical techniques and both the influence of the CN− coordination and of the bridging ligand have been studied. In the dimer where the bridging ligand is the π-conjugated 4,4′-bipy, the coordination of the cyanide ligand to the [Ru(2,2′-bipy)2] moiety shifts to more positive values all the E1/2 associated with the [Ru3O] core. The influence of the [Ru3O(CH3COO)6(py)2] fragment on the spectroscopic properties of [Ru(2,2′-bipy)2] has been probed by photophysical assays; at room temperature, no luminescence is detectable for the dimer where B = 4,4′-bipy, whereas the complex where B = bpa shows luminescence with low values of ϕ compared to the precursors [Ru(2,2′-bipy)2(B)(CN)]PF6. At 77 K both dimers show weak luminescence. Based on ΔG∘ values it is proposed that the main quenching pathway operates through an electron transfer mechanism.