Nonheme Oxoiron(IV) Complexed of Tris(2-pyridylmethyl)amine with cis-Monoanionic Ligands
Treatment of [Fe{sup IV}(O)(TPA)(NCMe)](CF{sub 3}SO{sub 3}){sub 2} [TPA, N,N,N-tris(2-pyridylmethyl)amine] with 3 equiv of NR{sub 4}X (X = CF{sub 3}CO{sub 2}, Cl, or Br) in MeCN at -40 C affords a series of metastable [Fe{sup IV}(O)(TPA)(X)]{sup +} complexes. Some characteristic features of the S = 1 oxoiron(IV) unit are quite insensitive to the ligand substitution in the equatorial plane, namely, the Fe-O distances (1.65-1.66 Angstroms), the energy ({approx}7114.5 eV) and intensity [25(2) units] of the 1s-to-3d transition in the X-ray absorption spectra, and the M{umlt o}ssbauer isomer shifts (0.01-0.06 mm{center_dot}s{sup -1}) and quadrupole splittings (0.92-0.95 mm{center_dot}s{sup -1}). The coordination of the anionic X ligand, however, is evidenced by red shifts of the characteristic near-IR ligand-field bands (720-800 nm) and spectroscopic observation of the bound anion by 19F NMR for X = CF{sub 3}CO{sub 2} and by EXAFS analysis for X = Cl (r{sub Fe-Cl} = 2.29 Angstroms) and Br (r{sub Fe-Br} = 2.43 Angstroms). Density functional theory calculations yield M{umlt o}ssbauer parameters and bond lengths in good agreement with the experimental data and produce excited-state energies that follow the trend observed in the ligand-field bands. Despite mitigating the high effective charge of the iron(IV) center, the substitution of the MeCN ligand with monoanionic ligands X{sup -} decreases the thermal stability of [Fe{sup IV}(O)(TPA)]{sup 2+} complexes. These anion-substituted complexes model the cis-X-Fe{sup IV}=O units proposed in the mechanisms of oxygen-activating nonheme iron enzymes.
- Research Organization:
- Brookhaven National Laboratory (BNL) National Synchrotron Light Source
- Sponsoring Organization:
- Doe - Office Of Science
- DOE Contract Number:
- AC02-98CH10886
- OSTI ID:
- 914098
- Report Number(s):
- BNL--78666-2007-JA
- Journal Information:
- Inorg. Chem., Journal Name: Inorg. Chem. Journal Issue: 16 Vol. 45; ISSN 0020-1669; ISSN INOCAJ
- Country of Publication:
- United States
- Language:
- English
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