Molecular and electronic structures of iron(II)/(III) complexes containing N,S-coordinated, closed-shell o-aminothiophenolato(1-) and o-iminothiophenolato(2-) ligands

The coordination chemistry of the ligands o-aminothiophenol, H(abt), 4,6-di-tert-butyl-2-aminothiophenol, H[L-AP], and 1,2-ethanediamine-N,N'-bis(2-benzenethiol), H-4('N2S2'), with FeCl2 under strictly anaerobic and increasingly aerobic conditions has been systematically investigated. Using strictly anaerobic conditions, the neutral, air-sensitive, yellow complexes (mu-S,S)[Fe-II(abt)(2)](2) (1), (mu-S,S)[Fe-II(L-AP)(2)](2)-8CH(3)OH (2), and (mu-S,S)[Fe-II('H2N2S2')](2)(CH3CN)-C-. (3) containing high spin ferrous ions have been isolated where (abt)(1-), (L-AP)(1-), and ('H2N2S2')(2-) represent the respective N,S-coordinated, aromatic o-aminothiophenolate derivative of these ligands. When the described reaction was carried out in the presence of trace amounts Of O-2 and [PPh4]Br, light-green crystals of [PPh4][Fe-II(abt)(2)(itbs)](.)[PPh4]Br (4) were isolated. The anion [Fe-II(abt)(2)(itbs)](-) contains a high spin ferrous ion, two N,S-coordinated o-aminophenolate(1-) ligands, and an S-bound, monoanionic o-iminothionebenzosemiquinonate(1-) pi radical, (itbs)(-). Complex 4 possesses an S-t = (3)/(2) ground state. In the absence of [PPh4]Br and presence of a base NEt3 and a little O-2, the ferric dimer (mu-NH,NH)[Fe-III(L-AP) (L-AP)](2) (5a) and its isomer (mu-S,S)[Fe-III(L-AP) (L-IP)](2) (5b) formed. (L-IP)(2-) represents the aromatic o-iminothiophenolate(2-) dianion of H[L-AP]. The structures of compounds 2, 4, and 5a have been determined by X-ray crystallography at 100(2) K. Zero-field Mossbauer spectroscopy of 1, 2, 3, and 4 unambiguously shows the presence of high spin ferrous ions: The isomer shift at 80 K is in the narrow range 0.85-0.92 mm s(-1), and a large quadrupole splitting, \DeltaE(Q)\, in the range 3.24-4.10 mm s(-1), is observed. In contrast, 5a and 5b comprise both intermediate spin ferric ions (S-FE = (3)/(2)) which couple antiferromagnetically in the dinuclear molecules yielding an S-t = 0 ground state.