Flach, M.; Hirsch, K.; Timm, M.; Ablyasova, O.S.; da Silva Santos, M.; Kubin, M.; Bülow, C.; Gitzinger, T.; Issendorff, B. von; Lau, J. T.; Zamudio-Bayer, V.: Iron L-3-edge energy shifts for the full range of possible 3d occupations within the same oxidation state of iron halides. Physical Chemistry Chemical Physics 24 (2022), p. 19890-19894
10.1039/d2cp02448a
Open Access Version
Abstract:
Oxidation states are integer in number but dn configurations of transition metal centers vary continuously in polar bonds. We quantify the shifts of the iron L3 excitation energy, within the same formal oxidation state, in a systematic L-edge X-ray absorption spectroscopy study of diatomic gas-phase iron(II) halide cations, [FeX]+,where X = F, Cl, Br, I. These shifts correlate with the electronegativity of the halogen, and are attributed exclusively to a fractional increase in population of 3d-derived orbitals along the series as supported by charge transfer multiplet simulations and density functional theory calculations. We extract an excitation energy shift of 420 meV ± 60 meV spanning the full range of possible 3d occupations between the most ionic bond in [FeF]+ and covalently bonded [FeI]+.