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Title: XAS Characterization of a Nitridoiron(IV) Complex with a Very Short Fe-N Bond

Abstract

X-ray absorption spectroscopy has been used to characterize the novel nitridoiron(IV) units in two [PhBP{sup R}{sub 3}]Fe(N) complexes (R = iPr and CyCH{sub 2}) and obtain direct spectroscopic evidence for a very short Fe-N distance. The distance of 1.51-1.55 {angstrom} reflects the presence of an Fe{triple_bond}N triple bond in accord with the observed Fe{triple_bond}N vibration observed for one of these species ({nu}{sub FeN} = 1034 cm{sup -1}). This highly covalent bonding interaction results in the appearance of an unusually intense pre-edge peak, whose estimated area of 100(20) units is much larger than those of the related tetrahedral complexes with Fe{sup I}-N{sub 2}-Fe{sup I}, Fe{sup II}-NPh{sub 2}, and Fe{sup III}NAd motifs, and those of recently described six-coordinate Fe{sup V}{triple_bond}N and Fe{sup VI}{triple_bond}N complexes. The observation that the Fe{sup IV}-N distances of two [PhBP{sup R}{sub 3}]Fe(N) complexes are shorter than the Fe{sup IV}-O bond lengths of oxoiron(IV) complexes may be rationalized on the basis of the greater {pi} basicity of the nitrido ligand than the oxo ligand and a lower metal coordination number for the Fe(N) complex.

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
929893
Report Number(s):
BNL-80475-2008-JA
Journal ID: ISSN 0020-1669; INOCAJ; TRN: US200822%%930
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Inorganic Chemistry; Journal Volume: 46; Journal Issue: 14
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; IRON NITRIDES; IRON COMPLEXES; ABSORPTION SPECTROSCOPY; BOND LENGTHS; CHEMICAL BONDS; COORDINATION NUMBER; X-RAY SPECTROSCOPY; national synchrotron light source

Citation Formats

Rohde,J., Betley, T., Jackson, T., Saouma, C., Peters, J., and Que, Jr., L. XAS Characterization of a Nitridoiron(IV) Complex with a Very Short Fe-N Bond. United States: N. p., 2007. Web. doi:10.1021/ic700818q.
Rohde,J., Betley, T., Jackson, T., Saouma, C., Peters, J., & Que, Jr., L. XAS Characterization of a Nitridoiron(IV) Complex with a Very Short Fe-N Bond. United States. doi:10.1021/ic700818q.
Rohde,J., Betley, T., Jackson, T., Saouma, C., Peters, J., and Que, Jr., L. Mon . "XAS Characterization of a Nitridoiron(IV) Complex with a Very Short Fe-N Bond". United States. doi:10.1021/ic700818q.
@article{osti_929893,
title = {XAS Characterization of a Nitridoiron(IV) Complex with a Very Short Fe-N Bond},
author = {Rohde,J. and Betley, T. and Jackson, T. and Saouma, C. and Peters, J. and Que, Jr., L.},
abstractNote = {X-ray absorption spectroscopy has been used to characterize the novel nitridoiron(IV) units in two [PhBP{sup R}{sub 3}]Fe(N) complexes (R = iPr and CyCH{sub 2}) and obtain direct spectroscopic evidence for a very short Fe-N distance. The distance of 1.51-1.55 {angstrom} reflects the presence of an Fe{triple_bond}N triple bond in accord with the observed Fe{triple_bond}N vibration observed for one of these species ({nu}{sub FeN} = 1034 cm{sup -1}). This highly covalent bonding interaction results in the appearance of an unusually intense pre-edge peak, whose estimated area of 100(20) units is much larger than those of the related tetrahedral complexes with Fe{sup I}-N{sub 2}-Fe{sup I}, Fe{sup II}-NPh{sub 2}, and Fe{sup III}NAd motifs, and those of recently described six-coordinate Fe{sup V}{triple_bond}N and Fe{sup VI}{triple_bond}N complexes. The observation that the Fe{sup IV}-N distances of two [PhBP{sup R}{sub 3}]Fe(N) complexes are shorter than the Fe{sup IV}-O bond lengths of oxoiron(IV) complexes may be rationalized on the basis of the greater {pi} basicity of the nitrido ligand than the oxo ligand and a lower metal coordination number for the Fe(N) complex.},
doi = {10.1021/ic700818q},
journal = {Inorganic Chemistry},
number = 14,
volume = 46,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • X-ray absorption spectroscopy has been used to characterize the novel nitridoiron(IV) units in two [PhBP{sup R}{sub 3}]Fe(N) complexes (R = iPr and CyCH{sub 2}) and obtain direct spectroscopic evidence for a very short Fe-N distance. The distance of 1.51--1.55 {angstrom} reflects the presence of an Fe{triple_bond}N triple bond in accord with the observed Fe{triple_bond}N vibration observed for one of these species (v{sub FeN}=1034 cm{sup -1}). This highly covalent bonding interaction results in the appearance of an unusually intense pre-edge peak, whose estimated area of 100(20) units is much larger than those of the related tetrahedral complexes with Fe{sup I}-N{sub 2}-Fe{supmore » I}, Fe{sup II}-NPh{sub 2}, and Fe{sup III}{triple_bond}NAd motifs, and those of recently described six-coordinate Fe{sup V}{triple_bond}N and Fe{sup VI}{triple_bond}N complexes. The observation that the Fe{sup IV}-N distances of two [PhBP{sup R}{sub 3}]Fe(N) complexes are shorter than the Fe{sup IV}-O bond lengths of oxoiron(IV) complexes may be rationalized on the basis of the greater ? basicity of the nitrido ligand than the oxo ligand and a lower metal coordination number for the Fe(N) complex.« less
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  • Four oxidation states of aqueous meso-5,10,15,20-tetrakis(2-N-methylpyridyl)porphinatoiron (Fe(2-TMPyP)(aq)) have been characterized at pH 9 and 12 via resonance Raman (RR), NMR, and ESR spectroscopic methods. These pH values were chosen because they are below and above the pK[sub a] values of the Fe(II) (11.2), Fe(III) (11.0), and Fe(IV) (10.0) complexes. The 2-TMPyP[sup 2+] ligand stabilizes four iron oxidation states, I-IV, in aqueous solution. ESR data of the highly reduced complex (g[perpendicular] = 2.32 and g[parallel] = 2.00) clearly demonstrate that Fe(II) reduction gives Fe(I) and not the porphyrin [pi]-anion radical at pH 9 and 12. This is the first Fe(I) complexmore » to be observed in aqueous solution, and the potentials of the Fe(II/I) couples ([minus]0.740 V at pH 9 and [minus]0.763 V at pH 12) are among the most positive of any yet observed for a porphinato complex. The first observation of a Fe[sup II]-OH stretch in a model heme complex is reported and assigned to a band at 464 cm[sup [minus]1] on the basis of its 20-cm[sup [minus]1] downshift in H[sub 2][sup 18]O. The Fe(IV/III) potentials at pH 9 and 12 are among the least positive ever reported for porphyrin complexes. For solutions with pH [gt] pK[sub a[Fe(IV)]], an Fe(IV) complex can be chemically or electrochemically generated and is stable for hours at room temperature. The stabilization of such a wide range of oxidation states is unprecedented in iron porphyrin chemistry and demonstrates that it is possible to modulate the coordination and redox chemistry of model hemes through variations in the electrostatic potential in which it resides without severely perturbing the intrinsic properties of the metalloporphine moiety.« less
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