Molecular and Electronic Structures of Iron Complexes Containing N,S-Coordinated, Open-Shell <i>o</i>-Iminothionebenzosemiquinonate(1−) π Radicals

The reaction of the dinuclear species (μ-NH,NH)[Fe<sup>III</sup>(L<sup>IP</sup>)(L<sup>AP</sup>)]<sub>2</sub> dissolved in CH<sub>2</sub>Cl<sub>2</sub> with dioxygen affords black microcrystals of diamagnetic (μ-S,S)[Fe<sup>III</sup>(L<sup>IP</sup>)(L<sup>ISQ</sup>)]<sub>2</sub>·<i>n</i>-hexane (<b>6</b>) upon the addition of <i>n</i>-hexane, where (L<sup>IP</sup>)<sup>2-</sup> represents the dianion of 4,6-di-<i>tert</i>-butyl-2-aminothiophenol, (L<sup>AP</sup>)<sup>-</sup> is the corresponding monoanion, and (L<sup>ISQ</sup>)<sup>-</sup> is the corresponding <i>o</i>-iminothionebenzosemiquinonate(1−) π radical monoanion; similarly, the dianion (‘H<sub>2</sub>N<sub>2</sub>S<sub>2</sub>‘)<sup>2-</sup> is derived from 1,2-ethanediamine-<i>N,N</i>‘-bis(2-benzenethiol), and (‘N<sub>2</sub>S<sub>2</sub><sup>•</sup>‘)<sup>3-</sup> is its monoradical trianion. The above reaction in a CH<sub>2</sub>Cl<sub>2</sub>/CH<sub>3</sub>OH (1:1) mixture yields the diamagnetic isomer (μ-NH,NH)[Fe<sup>III</sup>(L<sup>IP</sup>)(L<sup>ISQ</sup>)]<sub>2</sub>·5CH<sub>3</sub>OH (<b>7</b>), whereas air oxidation of (μ-S,S)[Fe<sup>II</sup>(‘H<sub>2</sub>N<sub>2</sub>S<sub>2</sub>‘)]<sub>2</sub> in CH<sub>3</sub>CN yields diamagnetic (μ-S,S)[Fe<sup>III</sup>(‘N<sub>2</sub>S<sub>2</sub><sup>•</sup>‘)]<sub>2</sub> (<b>8</b>). Complexes <b>6</b> and <b>8</b> were shown to undergo addition reactions with phosphines, phosphites, or cyanide affording the following complexes:  <i>trans</i>-[Fe<sup>II</sup>(L<sup>ISQ</sup>)<sub>2</sub>(P(OPh)<sub>3</sub>)] (<b>9</b>; <i>S</i><sub>t</sub> = 0) and [N(<i>n</i>-Bu)<sub>4</sub>][Fe<sup>II</sup>(L<sup>ISQ</sup>)<sub>2</sub>(CN)] (<i>S</i><sub>t</sub> = 0). Oxidation of <b>6</b> in CH<sub>2</sub>Cl<sub>2</sub> with iodine, bromine, and chlorine respectively yields black microcrystals of [Fe<sup>III</sup>(L<sup>ISQ</sup>)<sub>2</sub>X] (X = I, Br, or Cl) with <i>S</i><sub>t</sub> = <sup>1</sup>/<sub>2</sub>. The structures of complexes <b>6</b>−<b>9</b> have been determined by X-ray crystallography at 100 K. The oxidation level of the ligands and iron ions in all complexes has been unequivocally established, as indicated by crystallography; electron paramagnetic resonance, UV−vis, and Mössbauer spectroscopies; and magnetic-susceptibility measurements. The N,S<i>-</i>coordinated <i>o</i>-iminothionebenzosemiquinonate(1−) π radicals have been identified in all new complexes. The electronic structures of the new complexes have been determined, and it is shown that no evidence for iron oxidation states >III is found in this chemistry.