Anion Dependent Redox Changes in Iron Bis-terdentate Nitroxide {NNO} Chelates

Ian A. Gass, Christopher J. Gartshore, David W. Lupton, Boujemaa Moubaraki, Ayman Nafady, Alan M. Bond, John F. Boas, John D. Cashion, Carsten Milsmann, Karl Wieghardt, Keith S. Murray

Research output: Contribution to journalArticle

Abstract

The reaction of [Fe II(BF4)2]·6H2O with the nitroxide radical, 4,4-dimethyl-2,2-di(2-pyridyl) oxazolidine-N-oxide (L•), produces the mononuclear transition metal complex [FeII(L•)2](BF4)2 (1) which has been investigated using temperature dependent susceptibility, Mössbauer spectroscopy, electrochemistry, density functional theory (DFT) calculations, and X-ray structure analysis. Single crystal X-ray diffraction analysis and Mössbauer measurements reveal an octahedral low spin Fe2+ environment where the pyridyl donors from L• coordinate equatorially while the oxygen containing the radical from L• coordinates axially forming a linear O•··Fe(II)··O• arrangement. Magnetic susceptibility measurements show a strong radical-radical intramolecular antiferromagnetic interaction mediated by the diamagnetic Fe2+ center. This is supported by DFT calculations which show a mutual spatial overlap of 0.24 and a spin density population analysis which highlights the antiparallel spin alignment between the two ligands. Similarly the monocationic complex [FeIII(L-)2](BPh4)·0.5H2O (2) has been fully characterized with Fe ligand and N-O bond length changes in the X-ray structure analysis, magnetic measurements revealing a Curie-like S = 1/2 ground state, electron paramagnetic resonance (EPR) spectra, DFT calculations, and electrochemistry measurements all consistent with assignment of Fe in the (III) state and both ligands in the L- form. 2 is formed by a rare, reductively induced oxidation of the Fe center, and all physical data are self-consistent. The electrochemical studies were undertaken for both 1 and 2, thus allowing common Fe-ligand redox intermediates to be identified and the results interpreted in terms of square reaction schemes.
Original languageEnglish
Pages (from-to)3052-3064
Number of pages13
JournalInorganic Chemistry
Volume50
Issue number7
DOIs
Publication statusPublished - 8 Mar 2011

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    Gass, I. A., Gartshore, C. J., Lupton, D. W., Moubaraki, B., Nafady, A., Bond, A. M., Boas, J. F., Cashion, J. D., Milsmann, C., Wieghardt, K., & Murray, K. S. (2011). Anion Dependent Redox Changes in Iron Bis-terdentate Nitroxide {NNO} Chelates. Inorganic Chemistry, 50(7), 3052-3064. https://doi.org/10.1021/ic102588h