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, and 1,2-ethanediamine-N,A-bis(2-benzenethiol), 14(282ʹ), with FeCl2 under strictly anaerobic and increasingly aerobic conditions has been systematically investigated. Using strictly anaerobic conditions, the neutral, air-sensitive, yellow complexes -S,S)[Fe"(abt)2]2 (1), -S,S)[Fe"(L)2]2-8CH30H (2), and (-S,S)[Fe"(ʹH2N2S2ʹ)]2-CH3CN (3) containing high spin ferrous ions have been isolated where (abt), (L), and (...) 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 02 and [PPh4]Br, light-green crystals of [PPh4][Fe"(abt)2(itbs)]-[PPh4]Br (4) were isolated. The anion [Fe"(abt)2(itbs)]~ contains a high spin ferrous ion, two N,S-coordinated o-aminophenolate(1-) ligands, and an S-bound, monoanionic oiminothionebenzosemiquinonate(1-) n radical, (itbs). Complex 4 possesses an Si = 2 ground state. In the absence of [PPh4]Br and presence of a base NEts and a little O2, the ferric dimer -NH,NH)[Feʹ"(L)(LʹP)]2 (5a) and its isomer -S,S)[Fe"ʹ(L)(L2 (5b) formed. (U- represents the aromatic o-iminothiophenolate(2-) dianion of H[L]. 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 and a large quadrupole splitting, ((delta)Eol, in the range 3.24-4.10 mm s is observed. In contrast, 5a and 5b comprise both intermediate spin ferric ions (Spe = 2) which couple antiferromagnetically in the dinuclear molecules yielding an S = 0 ground state.