Four different redox states of the trinuclear ruthenium clusters of general formula [Ru3(μ3-O)(μ-CH3CO2)6(L)3] (L = xylyl isocyanide (1), tert-butyl isocyanide (2)) were generated electrochemically in solution and studied by reflectance infrared spectroelectrochemistry. The IR spectra in the v-(C≡N) region show multiple-band structure in the Ru(III)Ru(II)2 ( - 1) and uRu(III)2Ru(II) (0) states but a sharp single band in the Ru(III)3 (+1) or Ru(IV)Ru(III)2 (+2) state. Density functional theory (DFT) ab initio calculations were performed for free xylyl isocyanide and tert-butyl isocyanide. The results suggest that the C≡N - C bending mode interacts through Fermi resonance with the v(C≡N) fundamental for the 0 and - 1 states of both 1 and 2. The extensive redox chemistry of the Ru3-(μ3-O) clusters 1 and 2 offers a convenient means of effecting shifts in the energy of v(C≡N) bands of coordinated isocyanide ligands, in and out of Fermi resonance with the C≡N - C bending overtone.
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