Molecular and electronic structures of iron complexes containing N,S-coordinated, open-shell o-iminothionebenzosemiquinonate(1-),π radicals

The reaction of the dinuclear species (mu-NH,NH)[Fe-III(L-IP)(L-AP)](2) dissolved in CH2Cl2 with dioxygen affords black microcrystals of diamagnetic (mu-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-) pi 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 (mu-NH,NH)[Fe-III(L-IP)(L-ISQ)](2).5CH(3)OH (7), whereas air oxidation of (mu-S,S) [Fe-III('H2N2S2')](2) in CH3CN yields diamagnetic (mu-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)(2)X] (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 Mossbauer spectroscopies; and magnetic-susceptibility measurements. The N,S-coordinated o-iminothionebenzosemiquinonate(1-) pi 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.