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A Multiplet Analysis of Fe K-Edge 1s → 3d Pre-Edge Features of Iron Complexes

TitleA Multiplet Analysis of Fe K-Edge 1s → 3d Pre-Edge Features of Iron Complexes
Publication TypeJournal Article
Year of Publication1997
AuthorsWestre, TE, Kennepohl, P, DeWitt, JG, Hedman, B, Hodgson, KO, Solomon, EI
JournalJ. Am. Chem. Soc.
Volume119
Pagination6297–6314
Date Publishedjul
ISSN0002-7863
KeywordsPhD
Abstract

X-ray absorption Fe-K edge data on ferrous and ferric model complexes have been studied to establish a detailed understanding of the 1s –> 3d pre-edge feature and its sensitivity to the electronic structure of the iron site. The energy position and splitting, and intensity distribution, of the pre-edge feature were found to vary systematically with spin state, oxidation state, geometry, and bridging ligation (for binuclear complexes). A methodology for interpreting the energy splitting and intensity distribution of the 1s –> 3d pre-edge features was developed for high-spin ferrous and ferric complexes in octahedral, tetrahedral, and square pyramidal environments and low-spin ferrous and ferric complexes in octahedral environments. In each case, the allowable many-electron excited states were determined using ligand field theory. The energies of the excited states were calculated and compared to the energy splitting in the 1s –> 3d pre-edge features. The relative intensities of electric quadrupole transitions into the many-electron excited states were obtained and compared to the intensity pattern of the pre-edge feature. The effects of distorting the octahedral iron site to tetrahedral and square pyramidal geometries were analyzed. The contributions to the pre-edge intensity from both electric quadrupole and electric dipole (from 3d-4p mixing) intensity mechanisms were established for these distorted cases; the amount of 4p character and its distribution over the many-electron final states were experimentally estimated and compared to theoretical predictions from density functional calculations. The methodology was also applied to binuclear complexes, and a clear marker for the presence of a mu-oxo Fe-O-Fe bridge was established. General trends in 3d-4p mixing are developed and discussed for a series of geometries and oxidation states of Fe complexes. The results presented should further aid in the interpretation of the Is - 3d pre-edge region of iron complexes and non-heme iron enzymes.

URLhttp://pubs.acs.org/doi/abs/10.1021/ja964352a
DOI10.1021/ja964352a