Valence‐Delocalized and Valence‐Trapped Fe<sup>II</sup>Fe<sup>III</sup> Complexes: Drastic Influence of the Ligands

Dutta, Sujit; Ensling, Jürgen; Werner, Rüdiger; Flörke, Ülrich; Haase, Wolfgang; Gütlich, Philipp; Nag, Kamalaksha

doi:10.1002/anie.199701521

Cited by 71 publications

(49 citation statements)

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“…1 Nonetheless, when the temperature of acquisition is lowered to 4.2 K, a multiline spectrum for ( tbs L)Fe 3 (thf) is obtained (Figure S8), as observed in other molecular species. 24,37 The spectral features are broad and unresolved, consistent with overlapping sextets, indicative of a slowly relaxing internal magnetic field ( H int ). However, the magnetic relaxation rate exceeds that which is needed to display an out-of-phase

χ_{M}^{″}

signature in the ac magnetic susceptibility under zero-applied dc field since no maximum is observed, even at the lowest temperatures achievable (1.8 K).…”

Section: Resultsmentioning

confidence: 99%

“…H int develops from the slow relaxation of the electronic ground state | S , m s 〉 as described above. 37f The three sextets that reproduce the data in Figure 3a have the following parameters [ δ , Δ E Q (mm/s), H int ( T ): 0.45, 1.34, 25.1 (33%, blue trace); 0.46, 1.40, 27.5 (33%, green trace); and 0.63, 1.40, 22.7 (34%, brown trace)]. Using the same fitting algorithm, the data in Figure 3b was reproduced by a single sextet with [ δ , Δ E Q (mm/s), H int ( T ): 0.50, 1.22, 26.0].…”

Section: Resultsmentioning

confidence: 99%

“…Generally at high temperatures the internal field averages to zero and the ground and excited nuclear spin states are no longer Zeeman split; thus the data can be fit considering only the quadrupolar interaction. 37a In this regard, the spectrum for 1 obtained at 210 K (Figure 3i) was fit (red trace) with parameters [ δ and |Δ E Q | (mm/s): 0.45, 1.94].…”

Section: Resultsmentioning

confidence: 99%

“…The effect of electron delocalization has been documented in biological 6a,d,44 and synthetic 8,9,37e,45 polynuclear clusters where double exchange has been invoked as the mechanism through which high spin states are achieved. Herein we report the synthetic cluster [M][( tbs L)Fe 3 ] ([M] + = [(18-C-6)K(thf) 2 ] + ( 1 ) or [(crypt-222)K] + ( 2 )), a fully delocalized mixed-valent cluster that adopts a high spin electronic configuration.…”

Section: Discussionmentioning

confidence: 99%

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Maximizing Electron Exchange in a [Fe₃] Cluster

et al. 2016

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The one-electron reduction of (tbsL)Fe3(thf)1 furnishes [M][(tbsL)Fe3] ([M]+ = [(18-C-6)K(thf)2]+ (1, 76%) or [(crypt-222)K]+ (2, 54%)). Upon reduction, the ligand tbsL6− rearranges around the triiron core to adopt an almost ideal C3-symmetry. Accompanying the (tbsL) ligand rearrangement, the THF bound to the neutral starting material is expelled, and the Fe–Fe distances within the trinuclear cluster contract by ~0.13 Å in 1. Variable-temperature magnetic susceptibility data indicates a well-isolated S=+1112 spin ground state that persists to room temperature. Slow magnetic relaxation is observed at low temperature as evidenced by the out-of-phase χM″ component of the alternating current (ac) magnetic susceptibility data and by the appearance of hyperfine splitting in the zero-field 57Fe Mössbauer spectra at 4.2 K. Analysis of the ac magnetic susceptibility yields an effective spin reversal barrier (Ueff) of 22.6(2) cm−1, nearly matching the theoretical barrier of 38.7 cm−1 calculated from the axial zero-field splitting parameter (D = −1.29 cm−1) extracted from the reduced magnetization data. A polycrystalline sample of 1 displays three sextets in the Mössbauer spectrum at 4.2 K (Hext = 0) which converge to a single six-line pattern in a frozen 2-MeTHF glass sample, indicating a unique iron environment and thus strong electron delocalization. The spin ground state and ligand rearrangement are discussed within the framework of a fully delocalized cluster exhibiting strong double and direct exchange interactions.

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χ_{M}^{″}

signature in the ac magnetic susceptibility under zero-applied dc field since no maximum is observed, even at the lowest temperatures achievable (1.8 K).…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Maximizing Electron Exchange in a [Fe₃] Cluster

et al. 2016

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“…the anisotropic DE coupling leads to the ZFS (21) of the valencedelocalized E 0 À ð9=2Þ level. The splitting is proportional to the parameters A + (t l ), t 0 B + , t 0 C 9/2 of the anisotropic DE coupling (21). The non-diagonal matrix elements hU 0 À ð9=2; MÞkU 0 À ð9=2; M À 2Þi are determined by Eq.…”

Section: Introductionmentioning

confidence: 99%

Anisotropic double exchange in a valence-delocalized [Fe2.5+Fe2.5+] cluster. Spin–orbit coupling in the Anderson–Hasegawa double exchange model

Belinsky¹

2006

Chemical Physics

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Iron: Models of Proteins with Dinuclear Active SitesBased in part on the article Iron: Models of Proteins with Dinuclear Active Sites by Will E. Lynch & Donald M. Kurtz, Jr. which appeared in the Encyclopedia of Inorganic Chemistry, First Edition .

Chavez

Que

2005

Encyclopedia of Inorganic Chemistry

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The nonheme diiron enzymes are a class of metalloproteins that share a common function in the binding and activation of dioxygen. In recent years, interest in these enzymes has grown at a steady rate. The focus is both of a fundamental and applied nature. Understanding how these enzymes have evolved to perform synthetically challenging organic transformations under moderate conditions will provide insights into evolutionary processes and possibly help to develop techniques for engineering such active sites into proteins. These studies have led to the development of synthetic catalysts for these transformations through the ‘biomimetic’ approach. Through structural studies it has become clear that many of the metal binding sites in nonheme diiron enzymes possess carboxylate‐rich ligation, which is believed to be important in facilitating redox processes and structural rearrangements during catalysis. The use of model compounds to study these enzymes has many advantages that are not offered with other approaches. For example, a model for a proposed reactive intermediate may be stabilized at low temperature and studied. Synthetic compounds can also be selectively modified to examine the influence of a certain geometry, ligand set, or chemical environment on the properties and reactivity of the compound. In this article, several approaches are discussed toward the development of diiron model compounds. In one approach, multidentate ligands possessing two metal binding sites are examined. This approach has led to metal complexes with closely spaced iron centers, a key structural feature in these enzymes. In a second approach, mononuclear metal complexes supported by multidentate ligands are bridged by oxygen groups to generate the diiron core structure. A third approach focuses on dicarboxylate ligands that bridge the two iron centers. This approach allows for variation of the remaining terminal ligands. The fourth approach relies on steric interactions. Intramolecular ligand interactions are used to control the geometry of the diiron complex. To date, these four approaches have been very successful in generating many of the intermediates seen in the diiron enzyme catalytic cycles and a few have been shown to reproduce the catalytic activity to some extent. It is anticipated that many more insights will be garnered from model studies and that new chemistries will be discovered.

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Valence‐Delocalized and Valence‐Trapped Fe^IIFe^III Complexes: Drastic Influence of the Ligands

Cited by 71 publications

References 27 publications

Maximizing Electron Exchange in a [Fe₃] Cluster

Maximizing Electron Exchange in a [Fe₃] Cluster

Anisotropic double exchange in a valence-delocalized [Fe2.5+Fe2.5+] cluster. Spin–orbit coupling in the Anderson–Hasegawa double exchange model

Iron: Models of Proteins with Dinuclear Active SitesBased in part on the article Iron: Models of Proteins with Dinuclear Active Sites by Will E. Lynch & Donald M. Kurtz, Jr. which appeared in the Encyclopedia of Inorganic Chemistry, First Edition .

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Valence‐Delocalized and Valence‐Trapped FeIIFeIII Complexes: Drastic Influence of the Ligands

Cited by 71 publications

References 27 publications

Maximizing Electron Exchange in a [Fe3] Cluster

Maximizing Electron Exchange in a [Fe3] Cluster

Anisotropic double exchange in a valence-delocalized [Fe2.5+Fe2.5+] cluster. Spin–orbit coupling in the Anderson–Hasegawa double exchange model

Iron: Models of Proteins with Dinuclear Active SitesBased in part on the article Iron: Models of Proteins with Dinuclear Active Sites by Will E. Lynch & Donald M. Kurtz, Jr. which appeared in the Encyclopedia of Inorganic Chemistry, First Edition .

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Valence‐Delocalized and Valence‐Trapped Fe^IIFe^III Complexes: Drastic Influence of the Ligands

Maximizing Electron Exchange in a [Fe₃] Cluster

Maximizing Electron Exchange in a [Fe₃] Cluster