Probing the Electronic Structure of [2Fe-2S] Clusters with Three Coordinate Iron Sites by use of Photoelectron Spectroscopy
Five series of [2Fe-2S] complexes, [Fe{sub 2}S{sub 2}Cl{sub 2-x}(CN){sub x}]{sup -}, [Fe{sub 2}S{sub 2}(SEt){sub 2-x}Cl{sub x}]{sup -}, [Fe{sub 2}S{sub 2}(SEt)2-x(CN){sub x}]{sup -}, [Fe{sub 2}S{sub 2}Cl{sub 2-x}(OAc){sub x}]{sup -} (OAc = acetate), and [Fe{sub 2}S{sub 2}(SEt){sub 2-x}(OPr){sub x}]{sup -} (OPr = Propionate) (x = 0-2), were produced by collision induced dissociation of the corresponding [4Fe-4S] complexes and their electronic structures were studied using photoelectron spectroscopy. All the [2Fe-2S] complexes contain a [Fe{sub 2}S{sub 2}]{sup +} core similar to that in reduced [2Fe] Ferredoxins, but with different coordination geometries. For the first three series, which only involve tri-coordinated Fe sites, a linear relationship between the measured binding energies and the substitution number (x) was observed, revealing the independent ligand contributions to the total electron binding energies. The effect of the ligand increases in the order SEt {yields} Cl {yields} CN, conforming to their electron withdrawing ability in the same order. The carboxylate ligands in the [Fe{sub 2}S{sub 2}Cl{sub 2-x}(OAc){sub x}]{sup -} and [Fe{sub 2}S{sub 2}(SEt){sub 2-x}(OPr){sub x}]{sup -} complexes were observed to act as bi-dentate ligands, giving rise to tetra-coordinated iron sites. This is different from their mono-dentate coordination behavior in the [4Fe-4S] cubane complexes, reflecting the high reactivity of the unsatisfied three coordinate iron site in the [2Fe-2S] complexes. The [2Fe-2S] complexes with tetra-coordinated iron sites exhibit lower electron binding energies, i.e., higher reductive activity than the all tri-coordinate planar clusters. The electronic structures of all the [2Fe-2S] complexes were shown to conform to the ''inverted energy level scheme''.
- Research Organization:
- Pacific Northwest National Lab., Richland, WA (US), Environmental Molecular Sciences Laboratory (US)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 15016084
- Report Number(s):
- PNNL-SA-43730; 8592; KP1301030; TRN: US200509%%867
- Journal Information:
- Journal of Physical Chemistry A, Vol. 109, Issue 9; Other Information: PBD: 10 Mar 2005
- Country of Publication:
- United States
- Language:
- English
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