Biomimetic [2Fe‐2S] Clusters with Extensively Delocalized Mixed‐Valence Iron Centers

Abstract

A complete series of biomimetic [2Fe-2S] clusters, [(L(Dep) Fe)2 (μ-S)2 ] (3, L(Dep) =CH[CMeN(2,6-Et2 C6 H3 )]2 ), [(L(Dep) Fe)2 (μ-S)2 K] (4), [(L(Dep) Fe)2 (μ-S)2 ][Bu4 N] (5, Bu=n-butyl), and [(L(Dep) Fe)2 (μ-S)2 K2 ] (6), could be synthesized and characterized. The all-ferric [2Fe-2S] cluster 3 is readily accessible through the reaction of [(L(Dep) Fe)2 (μ-H)2 ] (2) with elemental sulfur. The chemical reduction of 3 with one molar equivalent of elemental potassium affords the contact ion pair K(+) [2Fe-2S](-) (4) as a one-dimensional coordination polymer, which in turn reacts with [Bu4 N]Cl to afford the separate ion pair [Bu4 N](+) [2Fe-2S](-) (5). Further reduction of 4 with potassium furnishes the super-reduced all-ferrous [2Fe-2S] cluster 6. Remarkably, complexes 4 and 5 are [2Fe-2S] clusters with extensively delocalized Fe(2+) Fe(3+) pairs as evidenced by (57) Fe Mössbauer, X-ray absorption and emission spectroscopy (XAS, XES) and in accordance with DFT calculations.

X-ray Absorption and Emission Spectroscopic Studies of [L2Fe2S2]n Model Complexes: Implications for the Experimental Evaluation of Redox States in Iron–Sulfur Clusters

“…Similar observations were recently reported by Driess and co-workers 27 for an analogous series of complexes, suggesting that this trend may be generalizable.…”

“…28−30 This series, first reported by one of our groups, is one of only two model systems for which all three redox states can be isolated. 27−30 As these complexes have been previously characterized by a combination of XRD, Mössbauer, and SQUID measurements (Table 1), they form a rigorous test set for the sensitivity of XAS and XES methods to one-electron redox events at the iron. Herein, the Fe K-edge XAS, S K-edge XAS, and Fe Kβ and valence-to-core (VtC) XES data for the complete series of [L 2 Fe 2 S 2 ] n ( n = 2-, 3-, 4-) complexes are reported.…”

From a Molecular 2Fe‐2Se Precursor to a Highly Efficient Iron Diselenide Electrocatalyst for Overall Water Splitting

“…The β‐diketiminato ligand supported the all‐ferric molecular 2Fe‐2Se cluster 2 , and its one‐electron reduced form 3 were prepared in a manner similar to the related 2Fe‐2S clusters (Scheme ; Supporting Information) . Both 2 and the anion in 3 displayed similar geometrical features (Figure ) as the analogous 2Fe‐2S clusters .…”

“…Both 2 and the anion in 3 displayed similar geometrical features (Figure ) as the analogous 2Fe‐2S clusters . Detailed spectroscopic investigations were undertaken to ascertain that 2 consists of high‐spin Fe III /Fe III , whereas 3 involves mixed‐valence Fe II /Fe III centers, such that the electronic structures of both 2 and 3 (Supporting Information, Table S5) are akin to those observed for the 2Fe‐2S analogue …”

From a Molecular 2Fe‐2Se Precursor to a Highly Efficient Iron Diselenide Electrocatalyst for Overall Water Splitting

“…[9a,b] To overcome this,the "lowtemperature molecular precursor" approach is ac onvenient method to control the composition and size distribution of nanomaterials and to enable high catalytic activity. [10] Unlike isolable 2Fe-2S clusters, [11] related 2Fe-2Se clusters are still scarce.Inaccordance with the seminal work of Holm and coworkers,several Fe-Se clusters were synthesized with arange of iron nuclearities (2, 3, 4, and 6);t hus aiming to understand the electronic effects exerted by heavy elements (such as selenium) in these clusters,a nd elucidate the function of such elements in biological systems. [10] Unlike isolable 2Fe-2S clusters, [11] related 2Fe-2Se clusters are still scarce.Inaccordance with the seminal work of Holm and coworkers,several Fe-Se clusters were synthesized with arange of iron nuclearities (2, 3, 4, and 6);t hus aiming to understand the electronic effects exerted by heavy elements (such as selenium) in these clusters,a nd elucidate the function of such elements in biological systems.…”