Hyperfine interactions and electron distribution in Fe(II)Fe(I) and Fe(I)Fe(I) models for the active site of the [FeFe] hydrogenases: Mössbauer spectroscopy studies of low-spin Fe(I)

doi:10.1007/s00775-013-1005-5

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Title:	Hyperfine interactions and electron distribution in Fe(II)Fe(I) and Fe(I)Fe(I) models for the active site of the [FeFe] hydrogenases: Mössbauer spectroscopy studies of low-spin Fe(I)
Authors:	Stoian Sebastian A.;Hsieh, Chung-Hung;Singleton Michael L.;Casuras Andrea F.;Darensbourg Marcetta Y.;McNeely Kelsey;Sweely Kurt;Popescu Codrina V.
Contributors:	淡江大學化學學系
Keywords:	Mössbauer spectroscopy;Hydrogenase;Model complex;Monovalent iron;Hyperfine interactions
Date:	2013-08
Issue Date:	2014-03-26 15:06:57 (UTC+8)
Publisher:	Heidelberg: Springer
Abstract:	Mössbauer studies of [{μ-S(CH2C(CH3)2CH2S}(μ-CO)FeIIFeI(PMe3)2(CO)3]PF6 (1 OX ), a model complex for the oxidized state of the [FeFe] hydrogenases, and the parent FeIFeI derivative are reported. The paramagnetic 1 OX 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 1 OX allow determination of the magnetic hyperfine couplings for the low-spin distal FeI ( FeI D ) site, A x,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. Mössbauer spectra of 1 OX 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{μ-S(CH2C(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 Mössbauer properties can be traced to this dz2 orbital. The structure of the magnetic hyperfine coupling tensor, A, of the low-spin FeI in 1 OX is discussed in the context of the known A tensors for the oxidized states of the [FeFe] hydrogenases.
Relation:	Journal of Biological Inorganic Chemistry 18(6), pp.609-622
DOI:	10.1007/s00775-013-1005-5
Appears in Collections:	[Graduate Institute & Department of Chemistry] Journal Article

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