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Bridging-hydride influence on the electronic structure of an [FeFe] hydrogenase active-site model complex revealed by XAES-DFT

Leidel, Nils ; Hsieh, Chung Hung ; Chernev, Petko ; Sigfridsson, Kajsa G.V. LU ; Darensbourg, Marcetta Y. and Haumann, Michael (2013) In Dalton Transactions 42(21). p.7539-7554
Abstract

Two crystallized [FeFe] hydrogenase model complexes, 1 = (μ-pdt)[Fe(CO)2(PMe3)]2 (pdt = SC1H 2C2H2C3H2S), and their bridging-hydride (Hy) derivative, [1Hy]+ = [(μ-H)(μ-pdt)[Fe(CO)2 (PMe 3)]2]+ (BF4-), were studied by Fe K-edge X-ray absorption and emission spectroscopy, supported by density functional theory. Structural changes in [1Hy]+ compared to 1 involved small bond elongations (<0.03 Å) and more octahedral Fe geometries; the Fe-H bond at Fe1 (closer to pdt-C2) was ∼0.03 Å longer than that at Fe2. Analyses of (1) pre-edge absorption spectra (core-to-valence transitions), (2)... (More)

Two crystallized [FeFe] hydrogenase model complexes, 1 = (μ-pdt)[Fe(CO)2(PMe3)]2 (pdt = SC1H 2C2H2C3H2S), and their bridging-hydride (Hy) derivative, [1Hy]+ = [(μ-H)(μ-pdt)[Fe(CO)2 (PMe 3)]2]+ (BF4-), were studied by Fe K-edge X-ray absorption and emission spectroscopy, supported by density functional theory. Structural changes in [1Hy]+ compared to 1 involved small bond elongations (<0.03 Å) and more octahedral Fe geometries; the Fe-H bond at Fe1 (closer to pdt-C2) was ∼0.03 Å longer than that at Fe2. Analyses of (1) pre-edge absorption spectra (core-to-valence transitions), (2) Kβ1,3, Kβ′, and Kβ2,5 emission spectra (valence-to-core transitions), and (3) resonant inelastic X-ray scattering data (valence-to-valence transitions) for resonant and non-resonant excitation and respective spectral simulations indicated the following: (1) the mean Fe oxidation state was similar in both complexes, due to electron density transfer from the ligands to Hy in [1Hy] +. Fe 1s→3d transitions remained at similar energies whereas delocalization of carbonyl AOs onto Fe and significant Hy-contributions to MOs caused an ∼0.7 eV up-shift of Fe1s→(CO)s,p transitions in [1Hy] +. Fed-levels were delocalized over Fe1 and Fe2 and degeneracies biased to Oh-Fe1 and C4v-Fe2 states for 1, but to O h-Fe1,2 states for [1Hy]+. (2) Electron-pairing of formal Fe(d7) ions in low-spin states in both complexes and a higher effective spin count for [1Hy]+ were suggested by comparison with iron reference compounds. Electronic decays from Fe d and ligand s,p MOs and spectral contributions from Hys,p→1s transitions even revealed limited site-selectivity for detection of Fe1 or Fe2 in [1Hy]+. The HOMO/LUMO energy gap for 1 was estimated as 3.0 ± 0.5 eV. (3) For [1Hy] + compared to 1, increased Fed (x2 - y2) - (z2) energy differences (∼0.5 eV to ∼0.9 eV) and Fed→d transition energies (∼2.9 eV to ∼3.7 eV) were assigned. These results reveal the specific impact of Hy-binding on the electronic structure of diiron compounds and provide guidelines for a directed search of hydride species in hydrogenases.

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published
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Dalton Transactions
volume
42
issue
21
pages
16 pages
publisher
Royal Society of Chemistry
external identifiers
  • scopus:84877724802
ISSN
1477-9226
DOI
10.1039/c3dt33042g
language
English
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no
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7e95e1df-2e3f-44a3-9b37-6e2f599595a9
date added to LUP
2020-01-15 10:16:54
date last changed
2020-06-24 06:01:11
@article{7e95e1df-2e3f-44a3-9b37-6e2f599595a9,
  abstract     = {<p>Two crystallized [FeFe] hydrogenase model complexes, 1 = (μ-pdt)[Fe(CO)<sub>2</sub>(PMe<sub>3</sub>)]<sub>2</sub> (pdt = SC1H <sub>2</sub>C2H<sub>2</sub>C3H<sub>2</sub>S), and their bridging-hydride (Hy) derivative, [1Hy]<sup>+</sup> = [(μ-H)(μ-pdt)[Fe(CO)<sub>2</sub> (PMe <sub>3</sub>)]<sub>2</sub>]<sup>+</sup> (BF<sub>4</sub><sup>-</sup>), were studied by Fe K-edge X-ray absorption and emission spectroscopy, supported by density functional theory. Structural changes in [1Hy]<sup>+</sup> compared to 1 involved small bond elongations (&lt;0.03 Å) and more octahedral Fe geometries; the Fe-H bond at Fe1 (closer to pdt-C2) was ∼0.03 Å longer than that at Fe2. Analyses of (1) pre-edge absorption spectra (core-to-valence transitions), (2) Kβ<sup>1,3</sup>, Kβ′, and Kβ<sup>2,5</sup> emission spectra (valence-to-core transitions), and (3) resonant inelastic X-ray scattering data (valence-to-valence transitions) for resonant and non-resonant excitation and respective spectral simulations indicated the following: (1) the mean Fe oxidation state was similar in both complexes, due to electron density transfer from the ligands to Hy in [1Hy] <sup>+</sup>. Fe 1s→3d transitions remained at similar energies whereas delocalization of carbonyl AOs onto Fe and significant Hy-contributions to MOs caused an ∼0.7 eV up-shift of Fe1s→(CO)s,p transitions in [1Hy] <sup>+</sup>. Fed-levels were delocalized over Fe1 and Fe2 and degeneracies biased to O<sub>h</sub>-Fe1 and C<sub>4v</sub>-Fe2 states for 1, but to O <sub>h</sub>-Fe1,2 states for [1Hy]<sup>+</sup>. (2) Electron-pairing of formal Fe(d<sup>7</sup>) ions in low-spin states in both complexes and a higher effective spin count for [1Hy]<sup>+</sup> were suggested by comparison with iron reference compounds. Electronic decays from Fe d and ligand s,p MOs and spectral contributions from Hys,p→1s transitions even revealed limited site-selectivity for detection of Fe1 or Fe2 in [1Hy]<sup>+</sup>. The HOMO/LUMO energy gap for 1 was estimated as 3.0 ± 0.5 eV. (3) For [1Hy] <sup>+</sup> compared to 1, increased Fed (x<sup>2</sup> - y<sup>2</sup>) - (z<sup>2</sup>) energy differences (∼0.5 eV to ∼0.9 eV) and Fed→d transition energies (∼2.9 eV to ∼3.7 eV) were assigned. These results reveal the specific impact of Hy-binding on the electronic structure of diiron compounds and provide guidelines for a directed search of hydride species in hydrogenases.</p>},
  author       = {Leidel, Nils and Hsieh, Chung Hung and Chernev, Petko and Sigfridsson, Kajsa G.V. and Darensbourg, Marcetta Y. and Haumann, Michael},
  issn         = {1477-9226},
  language     = {eng},
  month        = {06},
  number       = {21},
  pages        = {7539--7554},
  publisher    = {Royal Society of Chemistry},
  series       = {Dalton Transactions},
  title        = {Bridging-hydride influence on the electronic structure of an [FeFe] hydrogenase active-site model complex revealed by XAES-DFT},
  url          = {http://dx.doi.org/10.1039/c3dt33042g},
  doi          = {10.1039/c3dt33042g},
  volume       = {42},
  year         = {2013},
}