Speaker
Description
We are using a multi-edge, time-resolved x-ray spectroscopy approach to investigate how the solvent
environment controls reactivity in aqueous iron hexacyanide. This highly charged coordination complex
([Fe(CN)₆]⁴⁻) exhibits useful redox behavior ([Fe²⁺(CN)₆]⁴⁻ ⇌ [Fe³⁺(CN)₆]³⁻) alongside a minor ligand exchange
reaction in which CN⁻ is released and replaced by water. We ask whether systematic tuning of the solvation
shell (a mixture of water molecules and counterions) can control the quantum yield of this photoaquation
channel. Specifically, do particular counterion identities and concentrations bias the fast, collective solvent
response to photodissociated CN⁻ such that geminate recombination is complete, effectively restoring the
starting complex? Conversely, are there conditions under which cage escape is maximized, setting the stage for
downstream bimolecular chemistry such as Prussian blue formation? Key to answering these questions is the
ability to characterize solvation shell structure and dynamics during transient reaction stages. We argue that
multimodal time-resolved X-ray probes are well-poised to provide this information. This talk will present our
efforts using XAS at the Fe K- and L-edges, counterion (K, Na, Ca) K-edges and Fe 1s XES. We anticipate that
probes at the ligand and solvent K-edge and solution scattering (WAXS and time-resolved PDF) will be
powerful additions.
This work was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Chemical
Sciences, Geosciences, and Biosciences Division.