Faculté des sciences

Electronic structure and absorption spectra of biferrocenyl and bisfulvalenide diiron radical cations: detection and assignment of new low-energy transitions

Warratz, Ralf ; Aboulfadl, Hanane ; Bally, Thomas ; Tuczek, Felix

In: Chemistry - A European Journal, 2009, vol. 15, no. 7, p. 1604 - 1617

Low-energy electronic transitions have been detected spectroscopically in the FeII-FeIII mixed-valent biferrocenyl radical cation, but are absent in the spectra of the neutral analogue. They have been assigned by time-dependent DFT calculations (squares in figure). Analogous investigations were performed for the bisfulvalenide FeII-FeIII radical cation.... Mehr

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    Summary
    Low-energy electronic transitions have been detected spectroscopically in the FeII-FeIII mixed-valent biferrocenyl radical cation, but are absent in the spectra of the neutral analogue. They have been assigned by time-dependent DFT calculations (squares in figure). Analogous investigations were performed for the bisfulvalenide FeII-FeIII radical cation. UV-visible/near-IR (NIR)/mid-IR (MIR) solution, solid-state, and matrix-isolation electronic absorption spectra of the FeII-FeIII mixed-valent homobimetallic compounds biferrocenyl triiodide (1) and 1′,1′′′-diethylbiferrocenyltriiodide (2) reveal the presence of a low-energy transition in the MIR region that has not been reported before. The new absorption feature and the known NIR band are both assigned to intervalence charge-transfer (IVCT) transitions. To obtain insight into the electronic structures of 1 and 2, DFT calculations with the BP86 functionals and different basis sets have been performed. Based on the molecular orbital scheme of cation 1, one band corresponds to the transition between the highest occupied d₂-y² orbitals on the two iron centers, whereas the other one is assigned to a transition from a lower-lying d₂ orbital to the d₂-y² orbital. For comparison, the doubly bridged bisfulvalenide diiron cation (3) has been investigated by optical absorption spectroscopy and DFT calculations. The experimental and theoretical results are discussed with respect to the degree of electron localization/delocalization in these systems.