posted on 2020-06-29, 23:57authored byRaphael M. Jay, Vinícius Vaz da Cruz, Sebastian Eckert, Mattis Fondell, Rolf Mitzner, Alexander Föhlisch
In order to tailor
solution-phase chemical reactions involving
transition metal complexes, it is critical to understand how their
valence electronic charge distributions are affected by the solution
environment. Here, solute–solvent interactions of a solvatochromic
mixed-ligand iron complex were investigated using X-ray absorption
spectroscopy at the transition metal L2,3-edge. Due to
the selectivity of the corresponding core excitations to the iron
3d orbitals, the method grants direct access to the valence electronic
structure around the iron center and its response to interactions
with the solvent environment. A linear increase of the total L2,3-edge absorption cross section as a function of the solvent
Lewis acidity is revealed. The effect is caused by relative changes
in different metal–ligand-bonding channels, which preserve
local charge densities while increasing the density of unoccupied
states around the iron center. These conclusions are corroborated
by a combination of molecular dynamics and spectrum simulations based
on time-dependent density functional theory. The simulations reproduce
the spectral trends observed in the X-ray but also optical absorption
experiments. Our results underscore the importance of solute–solvent
interactions when aiming for an accurate description of the valence
electronic structure of solvated transition metal complexes and demonstrate
how L2,3-edge absorption spectroscopy can aid in understanding
the impact of the solution environment on intramolecular covalency
and the electronic charge distribution.