Charge and Spin-State Characterization of Cobalt Bis(o‑dioxolene) Valence Tautomers Using Co Kβ X‑ray Emission and L‑Edge X‑ray Absorption Spectroscopies

The valence tautomeric states of Co­(phen)­(3,5-DBQ)2 and Co­(tmeda)­(3,5-DBQ)2, where 3,5-DBQ is either the semiquinone (SQ–) or catecholate (Cat2–) form of 3,5-di-tert-butyl-1,2-benzoquinone, have been examined by a series of cobalt-specific X-ray spectroscopies. In this work, we have utilized the sensitivity of 1s3p X-ray emission spectroscopy (Kβ XES) to the oxidation and spin states of 3d transition-metal ions to determine the cobalt-specific electronic structure of valence tautomers. A comparison of their Kβ XES spectra with the spectra of cobalt coordination complexes with known oxidation and spin states demonstrates that the low-temperature valence tautomer can be described as a low-spin CoIII configuration and the high-temperature valence tautomer as a high-spin CoII configuration. This conclusion is further supported by Co L-edge X-ray absorption spectroscopy (L-edge XAS) of the high-temperature valence tautomers and ligand-field atomic-multiplet calculations of the Kβ XES and L-edge XAS spectra. The nature and strength of the magnetic exchange interaction between the cobalt center and SQ– in cobalt valence tautomers is discussed in view of the effective spin at the Co site from Kβ XES and the molecular spin moment from magnetic susceptibility measurements.