Valence-to-core (V2C) X-ray emission spectroscopy (XES) is recently made accessible and useful among the inorganic community. Our group very recently reported experimental Kβ V2C XES spectra for a series of low-spin octahedral Co(III) complexes with different ligand donors, in conjunction with DFT calculations (published in Dalton Trans., 2016, 45, 14191-14202). Cobalt Kβ V2C XES was demonstrated to be sensitive to the cobalt-ligand coordination environment, and in some cases even the change of just one or two ligand(s). Notably, our study revealed a previously unrecognized correlation between the spectrochemical series and the area of the V2C XES peaks, with strong field π acceptor ligands producing the largest V2C area. This correlation was explained by invoking different levels of π interaction between cobalt p orbitals and ligand orbitals that modulate the percentage of cobalt p orbital character in donor MOs, while changes in the average cobalt-ligand distance also play a role. One of the major advantages of XES has previously been demonstrated to be its ability to probe metal-ligand interactions and identify ligands. To date, these insights have largely been attributed to the σ bonding interactions between ligands and the metal center. Notably, our results herein show that for low-spin octahedral cobalt(III) centers, the level of π contributions could also be probed by this technique, thereby expanding the utility of V2C XES. At last, we will report our on-going work of developing a toolkit consisting of multiple X-ray spectroscopic methods and applying it to the study of nickel-catalyzed C-H bond activation and aldehyde decarbonylation.

Developing x-ray spectroscopic toolkits for mechanistic studies of cobalt and nickel catalysts

253rd National Meeting (2017)

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