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

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 E_1/2 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.