Resonance Raman spectra of chlorotetra-acetato- and chlorotetrabutyrato-diruthenium

Abstract

The metal–metal bonded species [Ru₂Cl(O₂CMe)₄] and [Ru₂Cl(O₂CPr)₄] both display a resonance Raman spectrum when irradiated with exciting lines which approach the wavenumber of the first electronic band maximum of each compound. The spectra are characterised in both cases by an overtone progression in the metal–metal stretching frequency, ν₁(Ru–Ru)a_1g, reaching 5ν₁ for [Ru₂Cl(O₂CMe)₄] and 4ν₁ for [Ru₂Cl(O₂CPr)₄]. Additionally, in the case of [Ru₂Cl(O₂CMe)₄] a second progression has been observed, extending as far as ν₂+ 3ν₁, where ν₂ is the ν₂(Ru–O)a_1g fundamental. The observation of such overtone progressions permits the determination of the spectroscopic constants ω₁ and X₁₁ for each molecule. The results form the basis for reassigning the electronic band in the visible region (the resonant electronic transition) of these compounds to the b_1uâ†�b_2g(δ*â†�δ) transition of the ruthenium–ruthenium moiety.