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Iron L-edge X-ray absorption spectroscopy of oxy-picket fence porphyrin: experimental insight into Fe-O2 bonding.
- Source :
-
Journal of the American Chemical Society [J Am Chem Soc] 2013 Jan 23; Vol. 135 (3), pp. 1124-36. Date of Electronic Publication: 2013 Jan 10. - Publication Year :
- 2013
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Abstract
- The electronic structure of the Fe-O(2) center in oxy-hemoglobin and oxy-myoglobin is a long-standing issue in the field of bioinorganic chemistry. Spectroscopic studies have been complicated by the highly delocalized nature of the porphyrin, and calculations require interpretation of multideterminant wave functions for a highly covalent metal site. Here, iron L-edge X-ray absorption spectroscopy, interpreted using a valence bond configuration interaction multiplet model, is applied to directly probe the electronic structure of the iron in the biomimetic Fe-O(2) heme complex [Fe(pfp)(1-MeIm)O(2)] (pfp ("picket fence porphyrin") = meso-tetra(α,α,α,α-o-pivalamidophenyl)porphyrin or TpivPP). This method allows separate estimates of σ-donor, π-donor, and π-acceptor interactions through ligand-to-metal charge transfer and metal-to-ligand charge transfer mixing pathways. The L-edge spectrum of [Fe(pfp)(1-MeIm)O(2)] is further compared to those of [Fe(II)(pfp)(1-MeIm)(2)], [Fe(II)(pfp)], and [Fe(III)(tpp)(ImH)(2)]Cl (tpp = meso-tetraphenylporphyrin) which have Fe(II)S = 0, Fe(II)S = 1, and Fe(III)S = 1/2 ground states, respectively. These serve as references for the three possible contributions to the ground state of oxy-pfp. The Fe-O(2) pfp site is experimentally determined to have both significant σ-donation and a strong π-interaction of the O(2) with the iron, with the latter having implications with respect to the spin polarization of the ground state.
Details
- Language :
- English
- ISSN :
- 1520-5126
- Volume :
- 135
- Issue :
- 3
- Database :
- MEDLINE
- Journal :
- Journal of the American Chemical Society
- Publication Type :
- Academic Journal
- Accession number :
- 23259487
- Full Text :
- https://doi.org/10.1021/ja3103583