A strongly coupled mixed valence state between Ru₃ clusters. Intramolecular electron transfer on the infrared vibrational time scale in a pyrazine (pz) bridged dimer of triruthenium clusters, [{Ru₃(μ₃-O) (μ- CH₃CO₂)₆(CO)(abco)}₂(μ-pz)] (abco = 1-azabicyclo[2,2,2]octane)

A pyrazine bridged dimer of triruthenium clusters [{(Ru(III)₂Ru(II)(μ₃-O)(μ-CH₃CO₂)₆(CO)(abco)}₂(μ-pz)] (abco = 1- azabicyclo[2,2,2]octane, pz = pyrazine) gives an inter-cluster mixed valence state upon one electron reduction. The splitting of the reduction waves in cyclic voltammetry, ΔE, was 470 mV. This corresponds to a comproportionation constant for formation of the mixed valence state of 9.0 x 10⁷. The IR spectrum of the mixed valence species in the ν(CO) region, measured by reflectance IR spectroelectrochemistry, showed a completely coalesced ν(CO) band. This represents delocalized redox behavior on the infrared vibrational timescale. The rate constant for intramolecular electron transfer was estimated to be 1 x 10¹² s^-1 at -18 °C by simulating the ν(CO) absorption bandshape. The mixed valence complex showed an intervalence charge transfer (ICT) band at 12500 cm^-1. Hush analysis provides a spectroscopic estimate of H(AB) to be 2490 cm^-1. Crystal structures of [{(Ru(III)₂Ru(II)(μ₃-O)(μ-CH₃CO₂)₆(CO)(abco)}₂(μ-pz)]·2CH₂Cl₂ and its precursor, [Ru(III)₂Ru(II)(μ₃- O)(CH₃CO₂)₆(CO)(abco)₂]·CH₂Cl₂, were determined by X-ray crystallography. Trends in Ru-O(oxo) and Ru-O(acetate) distances in these compounds show that the divalent site is localized on the Ru center attached to the carbonyl ligand.