Spectroscopic study of [Fe2O2(5-Et3-TPA)2]3+: Nature of the Fe2O2 diamond core and its possible relevance to high-valent binuclear non-heme enzyme intermediates

Andrew J. Skulan, Melissa A. Hanson, Hua Fen Hsu, Lawrence Que, Edward I. Solomon

Research output: Contribution to journalArticle

31 Citations (Scopus)

Abstract

The spectroscopic properties and electronic structure of an Fe2(III,IV) bis-μ-oxo complex, [Fe2O2-(5-Et3-TPA)2] (ClO4)3 where 5-Et3-TPA = tris(5-ethyl-2-pyridylmethyl)amine, are explored to determine the molecular origins of the unique electronic and geometric features of the Fe2O2 diamond core. Low-temperature magnetic circular dichroism (MCD) allows the two features in the broad absorption envelope (4000-30000 cm-1) to be resolved into 13 transitions. Their C/D ratios and transition polarizations from variable temperature-variable field MCD saturation behavior indicate that these divide into three types of electronic transitions; t2 → t2* involving excitations between metal-based orbitals with π Fe-O overlap (4000-10000 cm-1), t2/t2* → e involving excitations to metal-based orbitals with σ Fe-O overlap (12500-17000 cm-1) and LMCT (17000-30000 cm-1) and allows transition assignments and calibration of density functional calculations. Resonance Raman profiles show the C2h geometric distortion of the Fe2O2 core results in different stretching force constants for adjacent Fe-O bonds (kstr(Fe-Olong) = 1.66 and kstr(Fe-Oshort) = 2.72 mdyn/Å) and a small (∼20%) difference in bond strength between adjacent Fe-O bonds. The three singly occupied π*-metal-based orbitals form strong superexchange pathways which lead to the valence delocalization and the S = 3/2 ground state. These orbitals are key to the observed reactivity of this complex as they overlap with the substrate C-H bonding orbital in the best trajectory for hydrogen atom abstraction. The electronic structure implications of these results for the high-valent enzyme intermediates X and Q are discussed.

Original languageEnglish
Pages (from-to)7344-7356
Number of pages13
JournalJournal of the American Chemical Society
Volume125
Issue number24
DOIs
Publication statusPublished - 2003 Jun 18

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Diamond
Diamonds
Enzymes
Metals
Dichroism
Circular Dichroism
Electronic structure
Hydrogen
Temperature
Magnetic Fields
Ground state
Calibration
Stretching
Amines
Density functional theory
Trajectories
Polarization
Magnetic fields
Atoms
Substrates

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

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title = "Spectroscopic study of [Fe2O2(5-Et3-TPA)2]3+: Nature of the Fe2O2 diamond core and its possible relevance to high-valent binuclear non-heme enzyme intermediates",
abstract = "The spectroscopic properties and electronic structure of an Fe2(III,IV) bis-μ-oxo complex, [Fe2O2-(5-Et3-TPA)2] (ClO4)3 where 5-Et3-TPA = tris(5-ethyl-2-pyridylmethyl)amine, are explored to determine the molecular origins of the unique electronic and geometric features of the Fe2O2 diamond core. Low-temperature magnetic circular dichroism (MCD) allows the two features in the broad absorption envelope (4000-30000 cm-1) to be resolved into 13 transitions. Their C/D ratios and transition polarizations from variable temperature-variable field MCD saturation behavior indicate that these divide into three types of electronic transitions; t2 → t2* involving excitations between metal-based orbitals with π Fe-O overlap (4000-10000 cm-1), t2/t2* → e involving excitations to metal-based orbitals with σ Fe-O overlap (12500-17000 cm-1) and LMCT (17000-30000 cm-1) and allows transition assignments and calibration of density functional calculations. Resonance Raman profiles show the C2h geometric distortion of the Fe2O2 core results in different stretching force constants for adjacent Fe-O bonds (kstr(Fe-Olong) = 1.66 and kstr(Fe-Oshort) = 2.72 mdyn/{\AA}) and a small (∼20{\%}) difference in bond strength between adjacent Fe-O bonds. The three singly occupied π*-metal-based orbitals form strong superexchange pathways which lead to the valence delocalization and the S = 3/2 ground state. These orbitals are key to the observed reactivity of this complex as they overlap with the substrate C-H bonding orbital in the best trajectory for hydrogen atom abstraction. The electronic structure implications of these results for the high-valent enzyme intermediates X and Q are discussed.",
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Spectroscopic study of [Fe2O2(5-Et3-TPA)2]3+ : Nature of the Fe2O2 diamond core and its possible relevance to high-valent binuclear non-heme enzyme intermediates. / Skulan, Andrew J.; Hanson, Melissa A.; Hsu, Hua Fen; Que, Lawrence; Solomon, Edward I.

In: Journal of the American Chemical Society, Vol. 125, No. 24, 18.06.2003, p. 7344-7356.

Research output: Contribution to journalArticle

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T1 - Spectroscopic study of [Fe2O2(5-Et3-TPA)2]3+

T2 - Nature of the Fe2O2 diamond core and its possible relevance to high-valent binuclear non-heme enzyme intermediates

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AU - Solomon, Edward I.

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N2 - The spectroscopic properties and electronic structure of an Fe2(III,IV) bis-μ-oxo complex, [Fe2O2-(5-Et3-TPA)2] (ClO4)3 where 5-Et3-TPA = tris(5-ethyl-2-pyridylmethyl)amine, are explored to determine the molecular origins of the unique electronic and geometric features of the Fe2O2 diamond core. Low-temperature magnetic circular dichroism (MCD) allows the two features in the broad absorption envelope (4000-30000 cm-1) to be resolved into 13 transitions. Their C/D ratios and transition polarizations from variable temperature-variable field MCD saturation behavior indicate that these divide into three types of electronic transitions; t2 → t2* involving excitations between metal-based orbitals with π Fe-O overlap (4000-10000 cm-1), t2/t2* → e involving excitations to metal-based orbitals with σ Fe-O overlap (12500-17000 cm-1) and LMCT (17000-30000 cm-1) and allows transition assignments and calibration of density functional calculations. Resonance Raman profiles show the C2h geometric distortion of the Fe2O2 core results in different stretching force constants for adjacent Fe-O bonds (kstr(Fe-Olong) = 1.66 and kstr(Fe-Oshort) = 2.72 mdyn/Å) and a small (∼20%) difference in bond strength between adjacent Fe-O bonds. The three singly occupied π*-metal-based orbitals form strong superexchange pathways which lead to the valence delocalization and the S = 3/2 ground state. These orbitals are key to the observed reactivity of this complex as they overlap with the substrate C-H bonding orbital in the best trajectory for hydrogen atom abstraction. The electronic structure implications of these results for the high-valent enzyme intermediates X and Q are discussed.

AB - The spectroscopic properties and electronic structure of an Fe2(III,IV) bis-μ-oxo complex, [Fe2O2-(5-Et3-TPA)2] (ClO4)3 where 5-Et3-TPA = tris(5-ethyl-2-pyridylmethyl)amine, are explored to determine the molecular origins of the unique electronic and geometric features of the Fe2O2 diamond core. Low-temperature magnetic circular dichroism (MCD) allows the two features in the broad absorption envelope (4000-30000 cm-1) to be resolved into 13 transitions. Their C/D ratios and transition polarizations from variable temperature-variable field MCD saturation behavior indicate that these divide into three types of electronic transitions; t2 → t2* involving excitations between metal-based orbitals with π Fe-O overlap (4000-10000 cm-1), t2/t2* → e involving excitations to metal-based orbitals with σ Fe-O overlap (12500-17000 cm-1) and LMCT (17000-30000 cm-1) and allows transition assignments and calibration of density functional calculations. Resonance Raman profiles show the C2h geometric distortion of the Fe2O2 core results in different stretching force constants for adjacent Fe-O bonds (kstr(Fe-Olong) = 1.66 and kstr(Fe-Oshort) = 2.72 mdyn/Å) and a small (∼20%) difference in bond strength between adjacent Fe-O bonds. The three singly occupied π*-metal-based orbitals form strong superexchange pathways which lead to the valence delocalization and the S = 3/2 ground state. These orbitals are key to the observed reactivity of this complex as they overlap with the substrate C-H bonding orbital in the best trajectory for hydrogen atom abstraction. The electronic structure implications of these results for the high-valent enzyme intermediates X and Q are discussed.

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