Hyperfine interactions and electron distribution in FeIIFeI and FeIFeI models for the active site on the [FeFe]-hydrogenases : Mössbauer spectroscopy studies of low-spin FeI

Stoian, Sébastien A.;Hsieh, Chung-Hung;Singleton, Michael;Casuras, Andrea F.;Popescu, Codrina V.;et.al.
(2013) Journal of Biological Inorganic Chemistry — Vol. 18, p. 609-622 (2013)

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Authors
  • Stoian, Sébastien A.Carnegie-Mellon University (USA)
    Author
  • Hsieh, Chung-HungTexas A M University (USA)
    Author
  • Singleton, Michaelorcid-logoUCLouvain
    Author
  • Casuras, Andrea F.Ursinus College (USA)
    Author
  • Popescu, Codrina V.Ursinus College (USA)
    Author
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Abstract
Mo¨ssbauer studies of [{l-S(CH2C(CH3)2 CH2S}(l-CO)FeIIFeI(PMe3)2(CO)3]PF6 (1OX), a model complex for the oxidized state of the [FeFe] hydrogenases, and the parent FeIFeI derivative are reported. The paramagnetic 1OX is part of a series featuring a dimethylpropanedithiolate bridge, introducing steric hindrance with profound impact on the electronic structure of the diiron complex. Well-resolved spectra of 1OX allow determination of the magnetic hyperfine couplings for the low-spin distal FeI (FeI D) site, Ax,y,z= [-24 (6), -12 (2), 20 (2)] MHz, and the detection of significant internal fields (approximately 2.3 T) at the low-spin ferrous site, confirmed by density functional theory (DFT) calculations. Mo¨ssbauer spectra of 1OX show nonequivalent sites and no evidence of delocalization up to 200 K. Insight from the experimental hyperfine tensors of the FeI site is used in correlation with DFT to reveal the spatial distribution of metal orbitals. The Fe–Fe bond in [Fe2{l-S(CH2 C(CH3)2CH2S}(PMe3)2(CO)4] (1) involving two dz2-type orbitals is crucial in keeping the structure intact in the presence of strain. On oxidation, the distal iron site is not restricted by the Fe–Fe bond, and thus the more stable isomer results from inversion of the square pyramid, rotating the dz2 orbital of FeI D. DFT calculations imply that the Mo¨ssbauer properties can be traced to this dz2 orbital. The structure of the magnetic hyperfine coupling tensor, A, of the low-spin FeI in 1OX is discussed in the context of the known A tensors for the oxidized states of the [FeFe] hydrogenases.
Affiliations
  • Texas A&M University (USA)Department of Chemistry

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Stoian, S. A., Hsieh, C.-H., Singleton, M., Casuras, A. F., Darensbourg, M. Y., McNeely, K., Sweely, K., & Popescu, C. V. (2013). Hyperfine interactions and electron distribution in FeIIFeI and FeIFeI models for the active site on the [FeFe]-hydrogenases : Mössbauer spectroscopy studies of low-spin FeI. Journal of Biological Inorganic Chemistry, 18, 609-622. https://doi.org/10.1007/s00775-013-1005-5 (Original work published 2013)