Resonance Raman studies of transition metal peroxo complexes: 5—The oxygen carrier cobalt(II)‐salen and its μ‐peroxo complexes, [(L)(salen)Co]2O2; L = DMSO, py, DMF, pyO and no L

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Abstract
Resonance Raman spectra of the species [Co(salen)], [Co(salen)]2 and [Co(salen)(py)] were obtained both from the solids and from CHCl3 solutions. These spectra show a large number of bands in the 100–1750 cm−1 region which are assigned to vibrational modes of the salen ring. Oxygenated complexes having the general form μ‐peroxo‐[Co(salen)(L)]2O2, with ligand L being DMSO, py, DMF, pyO or no L and occupying the axial position trans to the dioxygen, gave resonance Raman spectra with many bands throughout the region 100–1750 cm−1. The ν(CoO) and ν (OO) wavenumbers in these complexes have been assigned by means of oxygen‐18 substitution. Force constants for the OO and COO bonds in the DMF complex have the values 380 and 247 N m−1, respectively. The effect of changing the ligand L on the observed wave numbers is interpreted in terms of both σ and π‐donor effects through the metal. Band intensity excitation profiles demonstrate that the O22− → Co3+ CT transition occurs at ˜370±10 nm for the complexes containing ligands L and at 580 nm for the complex with no L. Resonance function plots of Raman band intensities are interpreted in terms of the relative values of the OO bond orders which are shown to vary with the ligand L as follows: py>pyO>DMF>DMSO. This order is, however, at variance with that based on the ν (OO) wavenumbers.

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