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| Content Provider | PubMed Central |
|---|---|
| Author | Chakrabarti, Mrinmoy Deng, Liang Holm, R. H. Eckard, Münck Bominaar, Emile L. |
| Abstract | It is well established that the cysteinate-coordinated [Fe4S4] cluster of the Fe-protein of nitrogenase from A. vinelandii (Av2) can attain the all-ferrous core oxidation state. Mössbauer and EPR studies have shown that the all-ferrous cluster has a ground state spin S = 4 and an effective 3:1 site symmetry in the spin structure and 57Fe quadrupole interactions. Recently Deng and Holm reported the synthesis of [Fe4S4(Pr i 2NHCMe2)4],2 1, (Pr i 2NHCMe2 = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) and showed that the all-ferrous carbene-coordinated cluster is amenable to physico–chemical studies. Mössbauer and EPR studies of 1, reported here, reveal that the electronic structure of this complex is strikingly similar to that of the protein-bound cluster, suggesting that the ground state spin and the 3:1 site ratio are consequences of spontaneous distortions of the cluster core. To gain insight into the origin of the peculiar ground state of the all-ferrous clusters in 1 and Av2, we have studied a theoretical model that is based on a Heisenberg–Dirac–Van Vleck Hamiltonian whose exchange-coupling constants are a function of the Fe–Fe distances. By combining the exchange energies with the elastic deformation energies in the harmonic approximation, we obtain for a T2 distortion a minimum with spin S = 4 and a C3v core structure in which one iron is unique and three irons are equivalent. This minimum has all the spectroscopic and structural characteristics of the all-ferrous clusters of 1 and Av2. Our analysis maps the unique spectroscopic iron site to a specific site in the X-ray structure of the [4Fe-4S]0 core both in complex 1 and in Av2. |
| Related Links | http://dx.doi.org/10.1021/ic802192w |
| Starting Page | 2735 |
| File Format | |
| ISSN | 1520510X |
| e-ISSN | 1520510X |
| Journal | Inorganic chemistry |
| Issue Number | 7 |
| Volume Number | 48 |
| Language | English |
| Publisher Date | 2009-04-06 |
| Access Restriction | Open |
| Subject Keyword | Research in Higher Education |
| Content Type | Text |
| Resource Type | Article |
| Subject | Physical and Theoretical Chemistry Inorganic Chemistry |
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