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 trinuthenium clusters [{(Ru2RuII)-Ru-III(mu(3)-O)(mu-CH3CO2)(6)(CO)(abco)}(2)(mu-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, Delta E, was 470 mV. This corresponds to a comproportionation constant for formation of the mixed valence state of 9.0 x 10(7). The IR spectrum of the mixed valence species in the nu(CO) region, measured by reflectance IR spectroelectrochemistry, showed a completely coalesced nu(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 10(12) s(-1) at -18 degrees C by simulating the nu(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 [{(Ru2RuII)-Ru-III(mu(3)-O)(mu-CH3CO2)(6)(CO)(abco)}(2)(mu-pz)]. 2CH(2)Cl(2) and its precursor, [(Ru2RuII)-Ru-III(mu(3)-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.