Bibliographic Details
| Title: |
Combined Spectroscopic/Computational Study of Binuclear Fe(I)-Fe(I) Complexes: Implications for the Fully-Reduced Active-Site Cluster of Fe-Only Hydrogenases. |
| Authors: |
Fiedler, Adam T.1, Brunold, Thomas C.1 brunold@chem.wisc.edu |
| Source: |
Inorganic Chemistry. 3/21/2005, Vol. 44 Issue 6, p1794-1809. 16p. 7 Diagrams, 6 Charts, 15 Graphs. |
| Subjects: |
Iron compounds, Hydrogenase, Oxidoreductases, Inorganic compounds, Inorganic chemistry, Chemistry |
| Abstract: |
The Fe(I)-Fe(I) dimer complex [Fe2(pdt)(CO)4(CN)2][Et4N]2 (2), where pdt -- 1,3-propane dithiolate, serves as a model of the fully reduced [2Fe]H component of the H cluster, which is the active site for catalysis in Fe-only hydrogenases (FeHases). Electronic absorption, magnetic circular dichroism (MCD), and resonance Raman (rR) spectroscopies have been employed to characterize both the ground and excited states of 2 as well as those of the related complex Fe2(pdt)(CO)6 (1). These results have been combined with density functional theory (DFT) computations to produce experimentally validated bonding descriptions of 1 and 2. It is shown that Fe(I)-S covalency is significantly reduced upon dicyano substitution (i.e., conversion of 1 → 2), while the corresponding Fe(I)-CO/ CN π-backbonding interactions are strengthened, results that are corroborated by normal-coordinate analyses of the vibrational data. Detailed assignments of the features observed in the electronic absorption spectra of 1 and 2 have been developed on the basis of time-dependent DFT (TD-DFT) calculations, which provide remarkably accurate simulations of the experimental data. For both complexes, all bands below 32 000 cm-1 arise from transitions involving electronic excitation within the binuclear Fe-Fe core, with the most intense feature assigned to the Fe(σb) → Fe(σ*) transition. Analysis of the corresponding rR excitation profiles within the framework of time-dependent Heller theory reveals that in each case the Fe-Fe bond is elongated by ∼0.3 &ARing; in the Fe(σb) → Fe(σ*) excited state. Finally, building upon the insights gained from the spectroscopic/computational studies of 1 and 2, our computational methodology has been extended to the reduced enzyme active site, providing insights into the electronic structure of the [2Fe]H subcluster in the Hred state and its relationship to catalysis. [ABSTRACT FROM AUTHOR] |
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| Database: |
Engineering Source |
