Anion Dependent Redox Changes in Iron Bis-terdentate Nitroxide {NNO} Chelates GassIan A. GartshoreChristopher J. LuptonDavid W. MoubarakiBoujemaa NafadyAyman BondAlan M. BoasJohn F. CashionJohn D. MilsmannCarsten WieghardtKarl MurrayKeith S. 2011 The reaction of [Fe<sup>II</sup>(BF<sub>4</sub>)<sub>2</sub>]·6H<sub>2</sub>O with the nitroxide radical, 4,4-dimethyl-2,2-di(2-pyridyl) oxazolidine-<i>N</i>-oxide (L<sup>•</sup>), produces the mononuclear transition metal complex [Fe<sup>II</sup>(L<sup>•</sup>)<sub>2</sub>](BF<sub>4</sub>)<sub>2</sub> (<b>1</b>) 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 Fe<sup>2+</sup> environment where the pyridyl donors from L<sup>•</sup> coordinate equatorially while the oxygen containing the radical from L<sup>•</sup> coordinates axially forming a linear O<sup>•</sup>··Fe(II)··O<sup>•</sup> arrangement. Magnetic susceptibility measurements show a strong radical−radical intramolecular antiferromagnetic interaction mediated by the diamagnetic Fe<sup>2+</sup> 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 [Fe<sup>III</sup>(L<sup>−</sup>)<sub>2</sub>](BPh<sub>4</sub>)·0.5H<sub>2</sub>O (<b>2</b>) 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 <i>S</i> = 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<sup>−</sup> form. <b>2</b> 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 <b>1</b> and <b>2</b>, thus allowing common Fe-ligand redox intermediates to be identified and the results interpreted in terms of square reaction schemes.