Sequential oxidation of the cubane [4Fe--4S] cluster from [4Fe--4S](-) to [4Fe--4S](3+) in Fe(4)S(4)L(n)(-) complexes.
Gaseous Fe(4)S(n)(-) (n = 4-6) clusters and synthetic analogue complexes, Fe(4)S(4)L(n)(-) (L = Cl, Br, I; n = 1-4), were produced by laser vaporization of a solid Fe/S target and electrospray from solution samples, respectively, and their electronic structures were probed by photoelectron spectroscopy. Low binding energy features derived from minority-spin Fe 3d electrons were clearly distinguished from S-derived bands. We showed that the electronic structure of the simplest Fe(4)S(4)(-) cubane cluster can be described by the two-layer spin-coupling model previously developed for the [4Fe] cubane analogues. The photoelectron data revealed that each extra S atom in Fe(4)S(5)(-) and Fe(4)S(6)(-) removes two minority-spin Fe 3d electrons from the [4Fe--4S] cubane core and each halogen ligand removes one Fe 3d electron from the cubane core in the Fe(4)S(4)L(n)(-) complexes, clearly revealing a behavior of sequential oxidation of the cubane over five formal oxidation states: [4Fe--4S](-) --> [4Fe--4S](0) --> [4Fe--4S](+) --> [4Fe-4S](2+) --> [4Fe-4S](3+). The current work shows the electron-storage capability of the [4Fe--4S] cubane, contributes to the understanding of its electronic structure, and further demonstrates the robustness of the cubane as a structural unit and electron-transfer center.
Zhai
Hua-Jin
HJ
Department of Physics, Washington State University, 2710 University Drive, Richland, Washington 99352, USA.
Yang
Xin
X
Fu
You-Jun
YJ
Wang
Xue-Bin
XB
Wang
Lai-Sheng
LS
D000838:Anions; D005740:Gases; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D010084:Oxidation-Reduction; D013057:Spectrum Analysis / Q000379:methods; D013455:Sulfur / Q000737:chemistry*; D013816:Thermodynamics; D014835:Volatilization
D000838:Anions; D005740:Gases; D013455:Sulfur; D007501:Iron