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

The reaction of the dinuclear species (μ-NH,NH)[Fe^III(L^IP)(L^AP)]₂ dissolved in CH₂Cl₂ with dioxygen affords black microcrystals of diamagnetic (μ-S,S)[Fe^III(L^IP)(L^ISQ)]₂·n-hexane (6) upon the addition of n-hexane, where (L^IP)^2- represents the dianion of 4,6-di-tert-butyl-2-aminothiophenol, (L^AP)^- is the corresponding monoanion, and (L^ISQ)^- is the corresponding o-iminothionebenzosemiquinonate(1−) π radical monoanion; similarly, the dianion (‘H₂N₂S₂‘)^2- is derived from 1,2-ethanediamine-N,N‘-bis(2-benzenethiol), and (‘N₂S₂^•‘)^3- is its monoradical trianion. The above reaction in a CH₂Cl₂/CH₃OH (1:1) mixture yields the diamagnetic isomer (μ-NH,NH)[Fe^III(L^IP)(L^ISQ)]₂·5CH₃OH (7), whereas air oxidation of (μ-S,S)[Fe^II(‘H₂N₂S₂‘)]₂ in CH₃CN yields diamagnetic (μ-S,S)[Fe^III(‘N₂S₂^•‘)]₂ (8). Complexes 6 and 8 were shown to undergo addition reactions with phosphines, phosphites, or cyanide affording the following complexes:  trans-[Fe^II(L^ISQ)₂(P(OPh)₃)] (9; S_t = 0) and [N(n-Bu)₄][Fe^II(L^ISQ)₂(CN)] (S_t = 0). Oxidation of 6 in CH₂Cl₂ with iodine, bromine, and chlorine respectively yields black microcrystals of [Fe^III(L^ISQ)₂X] (X = I, Br, or Cl) with S_t = ¹/₂. The structures of complexes 6−9 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-coordinated o-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.