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Title: Unusual Synthetic Pathway for an {Fe(NO) 2} 9 Dinitrosyl Iron Complex (DNIC) and Insight into DNIC Electronic Structure via Nuclear Resonance Vibrational Spectroscopy

Abstract

Dinitrosyl iron complexes (DNICs) are among the most abundant NO-derived cellular species. Monomeric DNICs can exist in the {Fe(NO) 2} 9 or {Fe(NO) 2} 10 oxidation state (in the Enemark -Feltham notation). However, experimental studies of analogous DNICs in both oxidation states are rare, which prevents a thorough understanding of the di ff erences in the electronic structures of these species. Here, the {Fe(NO) 2} 9 DNIC [Fe(dmp)(NO) 2](OTf) ( 1 ; dmp = 2,9-dimethyl-1,10- phenanthroline) is synthesized from a ferrous precursor via an unusual pathway, involving disproportionation of an {FeNO} 7 complex to yield the {Fe(NO) 2} 9 DNIC and a ferric species, which is subsequently reduced by NO gas to generate a ferrous complex that re-enters the reaction cycle. In contrast to most {Fe(NO) 2} 9 DNICs with neutral N-donor ligands, 1 exhibits high solution stability and can be characterized structurally and spectroscopically. Reduction of 1 yields the corresponding {Fe(NO) 2} 10 DNIC [Fe(dmp)(NO) 2](2). The Mo ssbauer isomer shift of 2 is 0.08 mm/s smaller than that of 1 , which indicates that the iron center is slightly more oxidized in the reduced complex. The nuclear resonance vibrational spectra (NRVS) of 1 and 2 are distinct andmore » provide direct experimental insight into di ff erences in bonding in these complexes. In particular, the symmetric out-of-plane Fe -N - O bending mode is shifted to higher energy by 188 cm -1 in 2 in comparison to 1 . Using quantum chemistry centered normal coordinate analysis (QCC-NCA), this is shown to arise from an increase in Fe - NO bond order and a sti ff ening of the Fe(NO) 2 unit upon reduction of 1 to 2 . DFT calculations demonstrate that the changes in bonding arise from an iron- centered reduction which leads to a distinct increase in Fe - NO π -back-bonding in {Fe(NO) 2} 10 DNICs in comparison to the corresponding {Fe(NO) 2} 9 complexes, in agreement with all experimental findings. Finally, the implications of the electronic structure of DNICs for their reactivity are discussed, especially with respect to N-N bond formation in NO reductases.« less

Authors:
; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)
OSTI Identifier:
1376881
DOE Contract Number:  
AC02-06CH11357
Resource Type:
Journal Article
Journal Name:
Inorganic Chemistry
Additional Journal Information:
Journal Volume: 55; Journal Issue: 11; Journal ID: ISSN 0020-1669
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English

Citation Formats

Speelman, Amy L., Zhang, Bo, Silakov, Alexey, Skodje, Kelsey M., Alp, E. Ercan, Zhao, Jiyong, Hu, Michael Y., Kim, Eunsuk, Krebs, Karsten, and Lehnert, Nicolai. Unusual Synthetic Pathway for an {Fe(NO)2}9 Dinitrosyl Iron Complex (DNIC) and Insight into DNIC Electronic Structure via Nuclear Resonance Vibrational Spectroscopy. United States: N. p., 2016. Web. doi:10.1021/acs.inorgchem.6b00510.
Speelman, Amy L., Zhang, Bo, Silakov, Alexey, Skodje, Kelsey M., Alp, E. Ercan, Zhao, Jiyong, Hu, Michael Y., Kim, Eunsuk, Krebs, Karsten, & Lehnert, Nicolai. Unusual Synthetic Pathway for an {Fe(NO)2}9 Dinitrosyl Iron Complex (DNIC) and Insight into DNIC Electronic Structure via Nuclear Resonance Vibrational Spectroscopy. United States. https://doi.org/10.1021/acs.inorgchem.6b00510
Speelman, Amy L., Zhang, Bo, Silakov, Alexey, Skodje, Kelsey M., Alp, E. Ercan, Zhao, Jiyong, Hu, Michael Y., Kim, Eunsuk, Krebs, Karsten, and Lehnert, Nicolai. Mon . "Unusual Synthetic Pathway for an {Fe(NO)2}9 Dinitrosyl Iron Complex (DNIC) and Insight into DNIC Electronic Structure via Nuclear Resonance Vibrational Spectroscopy". United States. https://doi.org/10.1021/acs.inorgchem.6b00510.
@article{osti_1376881,
title = {Unusual Synthetic Pathway for an {Fe(NO)2}9 Dinitrosyl Iron Complex (DNIC) and Insight into DNIC Electronic Structure via Nuclear Resonance Vibrational Spectroscopy},
author = {Speelman, Amy L. and Zhang, Bo and Silakov, Alexey and Skodje, Kelsey M. and Alp, E. Ercan and Zhao, Jiyong and Hu, Michael Y. and Kim, Eunsuk and Krebs, Karsten and Lehnert, Nicolai},
abstractNote = {Dinitrosyl iron complexes (DNICs) are among the most abundant NO-derived cellular species. Monomeric DNICs can exist in the {Fe(NO)2}9 or {Fe(NO)2}10 oxidation state (in the Enemark -Feltham notation). However, experimental studies of analogous DNICs in both oxidation states are rare, which prevents a thorough understanding of the di ff erences in the electronic structures of these species. Here, the {Fe(NO)2}9 DNIC [Fe(dmp)(NO)2](OTf) ( 1 ; dmp = 2,9-dimethyl-1,10- phenanthroline) is synthesized from a ferrous precursor via an unusual pathway, involving disproportionation of an {FeNO}7 complex to yield the {Fe(NO)2}9 DNIC and a ferric species, which is subsequently reduced by NO gas to generate a ferrous complex that re-enters the reaction cycle. In contrast to most {Fe(NO)2}9 DNICs with neutral N-donor ligands, 1 exhibits high solution stability and can be characterized structurally and spectroscopically. Reduction of 1 yields the corresponding {Fe(NO)2}10 DNIC [Fe(dmp)(NO)2](2). The Mo ssbauer isomer shift of 2 is 0.08 mm/s smaller than that of 1 , which indicates that the iron center is slightly more oxidized in the reduced complex. The nuclear resonance vibrational spectra (NRVS) of 1 and 2 are distinct and provide direct experimental insight into di ff erences in bonding in these complexes. In particular, the symmetric out-of-plane Fe -N - O bending mode is shifted to higher energy by 188 cm-1 in 2 in comparison to 1 . Using quantum chemistry centered normal coordinate analysis (QCC-NCA), this is shown to arise from an increase in Fe - NO bond order and a sti ff ening of the Fe(NO)2 unit upon reduction of 1 to 2 . DFT calculations demonstrate that the changes in bonding arise from an iron- centered reduction which leads to a distinct increase in Fe - NO π -back-bonding in {Fe(NO)2}10 DNICs in comparison to the corresponding {Fe(NO)2}9 complexes, in agreement with all experimental findings. Finally, the implications of the electronic structure of DNICs for their reactivity are discussed, especially with respect to N-N bond formation in NO reductases.},
doi = {10.1021/acs.inorgchem.6b00510},
url = {https://www.osti.gov/biblio/1376881}, journal = {Inorganic Chemistry},
issn = {0020-1669},
number = 11,
volume = 55,
place = {United States},
year = {2016},
month = {6}
}