Spectroscopic and Theoretical Study of Spin-Dependent Electron Transfer in an Iron(III) Superoxo Complex

Heather D. Stout, Scott T. Kleespies, Chien Wei Chiang, Way Zen Lee, Lawrence Que, Eckard Münck, Emile L. Bominaar

Research output: Contribution to journalArticle

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Abstract

It was shown previously (J. Am. Chem. Soc. 2014, 136, 10846) that bubbling of O2 into a solution of FeII(BDPP) (H2BDPP = 2,6-bis[[(S)-2-(diphenylhydroxymethyl)-1-pyrrolidinyl]methyl]pyridine) in tetrahydrofuran at -80 °C generates a high-spin (SFe = 5/2) iron(III) superoxo adduct, 1. Mössbauer studies revealed that 1 is an exchange-coupled system, Ĥex=JŜFe·ŜR, where SR = 1/2 is the spin of the superoxo radical, of which the spectra were not well enough resolved to determine whether the coupling was ferromagnetic (S = 3 ground state) or antiferromagnetic (S = 2). The glass-forming 2-methyltetrahydrofuran solvent yields highly resolved Mössbauer spectra from which the following data have been extracted: (i) the ground state of 1 has S = 3 (J < 0); (ii) |J| > 15 cm-1; (iii) the zero-field-splitting parameters are D = -1.1 cm-1 and E/D = 0.02; (iv) the major component of the electric-field-gradient tensor is tilted ≈7° relative to the easy axis of magnetization determined by the MS = ±3 and ±2 doublets. The excited-state MS = ±2 doublet yields a narrow parallel-mode electron paramagnetic resonance signal at g = 8.03, which was used to probe the magnetic hyperfine splitting of 17O-enriched O2. A theoretical model that considers spin-dependent electron transfer for the cases where the doubly occupied π∗ orbital of the superoxo ligand is either "in" or "out" of the plane defined by the bent Fe-OO moiety correctly predicts that 1 has an S = 3 ground state, in contrast to the density functional theory calculations for 1, which give a ground state with both the wrong spin and orbital configuration. This failure has been traced to a basis set superposition error in the interactions between the superoxo moiety and the adjacent five-membered rings of the BDPP ligand and signals a fundamental problem in the quantum chemistry of O2 activation.

Original languageEnglish (US)
Pages (from-to)5215-5226
Number of pages12
JournalInorganic Chemistry
Volume55
Issue number11
DOIs
StatePublished - Jun 6 2016

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Ground state
electron transfer
Iron
iron
ground state
Electrons
Ligands
Quantum chemistry
orbitals
ligands
quantum chemistry
tetrahydrofuran
Excited states
adducts
Density functional theory
Tensors
Paramagnetic resonance
Magnetization
pyridines
electron paramagnetic resonance

Cite this

Stout, H. D., Kleespies, S. T., Chiang, C. W., Lee, W. Z., Que, L., Münck, E., & Bominaar, E. L. (2016). Spectroscopic and Theoretical Study of Spin-Dependent Electron Transfer in an Iron(III) Superoxo Complex. Inorganic Chemistry, 55(11), 5215-5226. https://doi.org/10.1021/acs.inorgchem.6b00134

Spectroscopic and Theoretical Study of Spin-Dependent Electron Transfer in an Iron(III) Superoxo Complex. / Stout, Heather D.; Kleespies, Scott T.; Chiang, Chien Wei; Lee, Way Zen; Que, Lawrence; Münck, Eckard; Bominaar, Emile L.

In: Inorganic Chemistry, Vol. 55, No. 11, 06.06.2016, p. 5215-5226.

Research output: Contribution to journalArticle

Stout, Heather D. ; Kleespies, Scott T. ; Chiang, Chien Wei ; Lee, Way Zen ; Que, Lawrence ; Münck, Eckard ; Bominaar, Emile L. / Spectroscopic and Theoretical Study of Spin-Dependent Electron Transfer in an Iron(III) Superoxo Complex. In: Inorganic Chemistry. 2016 ; Vol. 55, No. 11. pp. 5215-5226.
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