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Disentangling Transient Charge Density and Metal–Ligand Covalency in Photoexcited Ferricyanide with Femtosecond Resonant Inelastic Soft X-ray Scattering

2018; American Chemical Society; Volume: 9; Issue: 12 Linguagem: Inglês

10.1021/acs.jpclett.8b01429

1948-7185

Raphael M. Jay, Jesper Norell, Sebastian Eckert, Markus Hantschmann, Martin Beye, Brian Kennedy, Wilson Quevedo, W. F. Schlotter, Georgi L. Dakovski, Michael P. Minitti, Matthias C. Hoffmann, Ankush Mitra, Stefan Moeller, Dennis Nordlund, Wenkai Zhang, Huiyang W. Liang, Kristjan Kunnus, Katharina Kubiček, Simone Techert, Marcus Lundberg, Philippe Wernet, Kelly J. Gaffney, Michael Odelius, Alexander Föhlisch,

Iron oxide chemistry and applications

Soft X-ray spectroscopies are ideal probes of the local valence electronic structure of photocatalytically active metal sites. Here, we apply the selectivity of time-resolved resonant inelastic X-ray scattering at the iron L-edge to the transient charge distribution of an optically excited charge-transfer state in aqueous ferricyanide. Through comparison to steady-state spectra and quantum chemical calculations, the coupled effects of valence-shell closing and ligand-hole creation are experimentally and theoretically disentangled and described in terms of orbital occupancy, metal-ligand covalency, and ligand field splitting, thereby extending established steady-state concepts to the excited-state domain. π-Back-donation is found to be mainly determined by the metal site occupation, whereas the ligand hole instead influences σ-donation. Our results demonstrate how ultrafast resonant inelastic X-ray scattering can help characterize local charge distributions around catalytic metal centers in short-lived charge-transfer excited states, as a step toward future rationalization and tailoring of photocatalytic capabilities of transition-metal complexes.