A neutral triple-helical trinuclear oxo-centered mixed-valent iron complex: Mössbauer spectroscopic and magnetic susceptibility studies

Coropceanu, Veaceslav; Schünemann, Volker; Ober, C.; Gerdan, Michael; Trautwein, Alfred X.; Köhler, Jürgen; Saalfrank, Rolf W.

doi:10.1016/s0020-1693(00)00003-7

Cited by 9 publications

(6 citation statements)

References 11 publications

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“…The Mössbauer spectrum of complex 6 is similar to that observed for another trimeric, mixed‐valent, oxo‐centered complex,69 although it is remarkably different from other trimeric, mixed‐valence, oxo‐centered complexes 70,71. The doublets in the Mössbauer spectrum of 6 at room temperature are far from the ratio of 2:1, with isomer shifts and quadrupole splittings of δ I = 0.27 mm·s −1 , Δ E QI = 1.75 mm·s −1 and δ II = 0.72 mm·s −1 , Δ E QII = 2.63 mm·s −1 (Figure 9).…”

Section: Resultssupporting

confidence: 65%

“…This denotes some degree of delocalization (valence detrapping) of the extra electron over the three Fe sites. At room temperature only one doublet is usually found for trimeric, mixed‐valent, oxo‐centered transition metal complexes due to full delocalization of the “excess” electron over the three iron sites (“valence‐detrapped state”) 69,70. Complex 6 exhibits a partially valence‐delocalized (partially valence‐detrapped) state which is similar to the case of a reported Fe II /Fe III complex 69…”

Section: Resultsmentioning

confidence: 55%

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Transition Metal Ion Directed Self‐Assembly of Polynuclear Coordination Complexes: Structural Characterization and Magnetic Properties

et al. 2004

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Section: Resultssupporting

confidence: 65%

Section: Resultsmentioning

confidence: 55%

Transition Metal Ion Directed Self‐Assembly of Polynuclear Coordination Complexes: Structural Characterization and Magnetic Properties

et al. 2004

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“…Temperature-dependent magnetisation measurements support the assignment of the component oxidation states in 2 with antiferromagnetic coupling. 13 Using the HDVV spin-only model with the Hamiltonian:…”

Section: Discussionmentioning

confidence: 99%

“…In a preliminary study 12 of 2, Mössbauer spectra indicated that the iron valencies are localised, at least at 4.2 K, whereas the electrochemical data at first sight suggested delocalisation. Meanwhile, temperature-dependent Mössbauer spectra have been analysed 13 to show the existence of partially delocalised states in the solid state throughout the whole temperature range. To provide further insight into the electronic structure of this system we have now performed a range of further measurements, crystallographic, spectroscopic, electrochemical, and spectroelectrochemical, and we have compared the mixed-valence cluster with the oxidised tri-iron() and analogous mixed-metal complexes.…”

Section: Daltonmentioning

confidence: 99%

Electron transfer in a trinuclear oxo-centred mixed-valence iron complex, in solid and solution statesDedicated to Professor Dieter Sellmann on the occasion of his 60th birthday.

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Köhler³

et al. 2001

J. Chem. Soc., Dalton Trans.

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Complexes [Fe III 2 M II OL 3 ] (M = Fe, Co, Ni, Cu; 2, 3, 4, 5) have been synthesised in which L 2Ϫ is a pentadentate ligand designed to coordinate all three metal atoms in the central cluster and to inhibit dissociation and solvent exchange processes. Crystal structures for 2, 4 and 5 show threefold symmetry, attributed to rotational disorder. Magnetisation data for 2 indicate strong superexchange between basis oxidation states Fe(3ϩ, 3ϩ, 2ϩ). Comparisons of IR spectra across the series of complexes confirm the non-threefold symmetry of the mixed-valence cluster on the vibrational time scale, both in the solid state and in solution. Proton NMR spectra in solution at room temperature do not distinguish the three iron sites, suggesting that pseudo-rotation by thermal electron transfer also operates. Cyclic voltammetry and spectroelectrochemical measurements show that the mixed-valence iron complex 2 can be oxidised reversibly to give the tri-iron() complex [Fe 3 OL 3 ] ϩ and reduced reversibly and quasireversibly to give respectively [Fe 3 OL 3 ] Ϫ and tri-iron() [Fe 3 OL 3 ] 2Ϫ , E 0 = 85, Ϫ635, Ϫ1230 mV (versus Fc ϩ/0 ) in dichloromethane (T = 298 K, 0.1 M [n-Bu 4 N][PF 6 ]). Mössbauer spectra of 2 indicate significant valence delocalisation even at low temperature (4.2 K) with estimated valences Fe(2.9ϩ, 2.9ϩ, 2.2ϩ) in the solid state. At higher temperatures no lifetime broadening is observed but additional Mössbauer absorptions are consistent with increasing proportions of trimer molecules with greater delocalisation, i.e. Fe(2.75ϩ, 2.75ϩ, 2.5ϩ). In frozen solution (THF) the spectra indicate increasing proportions of molecules fully valence-delocalised on the Mössbauer time scale. The data are accounted for with a model which places the complex at the Robin-Day class III/II borderline. It combines strong superexchange with significant double exchange even at the lowest temperatures, while at higher temperatures in solution complete valence delocalisation occurs through intramolecular electron transfer at rates intermediate between the IR and NMR time scales.

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“…Fully deconfined minority-spin electrons occurring at neighboring Fe 2+ and Fe 3+ sites with equal probability represent symmetric dimers = 0.5. Partially delocalized minority-spin electrons, 0 < <0.5, have a higher probability of being at one of the neighboring sites in an asymmetric dimer due to a barrier to excursion, for example, from electron-lattice coupling [46,47]. If these mixed-valence cases manifest as long-range charge modulation, then these are site-centered CO ( = 0), bond-centered CO ( = 0.5), and an admixture (coexistence) of site-and bond-centered CO (0 < <0.5).…”

Section: Experimental Methods and Resultsmentioning

confidence: 99%

Coexistence of site- and bond-centered electron localization in the high-pressure phase ofLuFe2O4

et al. 2016

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Magnetic-electronic hyperfine interaction parameters of spectral components are obtained from in situ 57 Fe Mössbauer spectroscopy pressure studies of the mixed-valence LuFe 2 O 4 multiferroic, up to ∼30 GPa and on recovered high-pressure phase samples. Temperature-dependent Mössbauer spectra of the low-pressure phase show that Fe 2+ and Fe 3+ sites are discernible, consistent with known site-centered charge order in the triangular (frustrated) Fe sublattice network. Magnetic spectra of the high-pressure phase, stabilized in a rectangular Fe sublattice network at P>8 GPa, exhibit fingerprints of iron in an intermediate valence state only. Temperature-dependent resistivity pressure studies evidence thermally activated small polaron motion in the high-pressure phase. These experimental signatures, complemented by ab initio calculations of electronic structure, are considered evidence of asymmetric dimer formation Fe (2+ +) ⇔ Fe (3−)+ ,w h e r e the minority-spin electron deconfinement coefficient is = 0.3−0.4. Bragg satellites discerned in electron diffraction patterns of the metastable high-pressure phase possibly stem from this admixture of site-and bond-centered localization (intermediate-state charge order) in a magnetic background. This breaks inversion symmetry and potentially renders LuFe 2 O 4 in its high-pressure phase as a new charge order instigated (electronic) ferroelectric.

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A neutral triple-helical trinuclear oxo-centered mixed-valent iron complex: Mössbauer spectroscopic and magnetic susceptibility studies

Cited by 9 publications

References 11 publications

Transition Metal Ion Directed Self‐Assembly of Polynuclear Coordination Complexes: Structural Characterization and Magnetic Properties

Transition Metal Ion Directed Self‐Assembly of Polynuclear Coordination Complexes: Structural Characterization and Magnetic Properties

Electron transfer in a trinuclear oxo-centred mixed-valence iron complex, in solid and solution statesDedicated to Professor Dieter Sellmann on the occasion of his 60th birthday.

Coexistence of site- and bond-centered electron localization in the high-pressure phase ofLuFe2O4

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