Stadler, Christian and Daub, Joerg and Koehler, Jürgen and Saalfrank, Rolf W. and Coropceanu, Veaceslav and Schuenemann, Volker and Ober, Claudia and Trautwein, Alfred X. and Parker, Stewart F. and Poyraz, Mehmet and Inomata, Tomohiko and Cannon, Roderick D. (2001) Electron transfer in a trinuclear oxo-centred mixed-valence iron complex, in solid and solution states. JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS (22). pp. 3373-3383. ISSN 1472-7773
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Complexes [(Fe2MOL3)-M-III-O-II] (M = Fe, Co, Ni, Cu; 2, 3, 4, 5) have been synthesised in which L2- 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(3+, 3+, 2+). Comparisons of IR spectra across the series of complexes con rm 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(III) complex [Fe3OL3](+) and reduced reversibly and quasireversibly to give respectively [Fe3OL3](-) and tri-iron(II) [Fe3OL3](2-), E-0 = 85, -635, -1230 mV (versus Fc(+/0)) in dichloromethane (T = 298 K, 0.1 M [n-Bu4N][PF6]). Mossbauer spectra of 2 indicate significant valence delocalisation even at low temperature (4.2 K) with estimated valences Fe(2.9+, 2.9+, 2.2+) in the solid state. At higher temperatures no lifetime broadening is observed but additional Mossbauer absorptions are consistent with increasing proportions of trimer molecules with greater delocalisation, i.e. Fe(2.75+, 2.75+, 2.5+). In frozen solution (THF) the spectra indicate increasing proportions of molecules fully valence-delocalised on the Mossbauer 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.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | FATTY-ACID ANIONS; PHASE-TRANSITIONS; VIBRATIONAL-SPECTRA; IRON(III,III,II) CLUSTER; CARBOXYLATE COMPLEXES; NEUTRON-SCATTERING; ACETATE COMPLEXES; METAL-COMPLEXES; TRANSFER RATES; HEAT-CAPACITY; |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Institut für Organische Chemie > Alumni or Retired Professors > Prof. Dr. Jörg Daub |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 01 Mar 2022 10:35 |
| Last Modified: | 01 Mar 2022 10:35 |
| URI: | https://pred.uni-regensburg.de/id/eprint/41903 |
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