Trinuclear Pyrazine-Bridged Ruthenium Complexes: Syntheses, Electrochemistry, NIR−Vis Spectra, and Their Interpretation in Terms of a 5-Orbital−3-Parameter Model

Abstract
A study of absorption spectra in the near-infrared (NIR) and visible (vis) regions of trinuclear Ru complexes containing pyrazine (pyz) as bridging ligand, trans-[{Ru(NH3)5pyz}2Ru(NH3)4]m+ (m = 6−9), is reported. The spectra were recorded on aqueous solutions containing the described species formed in situ by stoichiometric additions of a standard solution of Ce(SO4)2. They were interpreted in terms of a simple 5-orbital−3-parameter model which includes the effects of d−π* interaction and electronic correlation. The model is shown to account for the observed NIR−vis spectra of the complex ions. The 6+ parent species was synthesized by an improved literature method and fully characterized. The novel 8+ complex was also prepared and characterized. The 9+ ion was established to be slowly reduced by water, with dioxygen formation. Electrochemical (CV and DPV) studies were performed on the trinuclear 6+ complex, as well as on its constituent fragments [Ru(NH3)5(pyz)]2+ and trans-[Ru(NH3)4(pyz)2]2+.

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