Structural and spectroscopic characterization of a five-coordinate {Fe(NO)}6 complex derived from an iron complex with carboxamido N and thiolato S donors

An iron(III) complex, [Fe(N2S2)CI](Et4N)2 (1) with a mixed carboxamido nitrogen and thiolato sulfur donor set derived from (2-mercapto-isobutyryl)-o-phenylene diamine was prepared. The iron(III) is in a square pyramidal ligand environment. EPR, Mössbauer and variable-temperature susceptibility establishes that 1 possesses an S=3/2 ground state. The iron(III) oxidation state is stable over a 1.5 V range (Epc[Fe(N2S2)Cl]3−/2− =−1290 mV and Epa [Fe(N2S2)Cl]2−/1−=+220 mV versus SCE in CH3CN). Complex 1 reacted with a stoichiometric amount of NO yielding an air stable [Fe(N2S2)(NO)](Et4N) complex 2 which belongs, as does the [Fe(S2C4N2)2(NO](Et4N) nitrosyl dithiotene complex 4 to the {Fe(NO)}6 group. Both complexes have a square pyramidal structure with a linear FeNO moiety and a very short FeN(O) bond distance of 1.633 (2) and 1.612 Å (4). They differ by the position of the νNO stretching frequency located at 1780 cm−1 for 2 and 1840 cm−1 for 4. Magnetic susceptibility measurements indicated the diamagnetic nature of both complexes. The Mössbauer spectra of complexes 1, 2, 3 ([Fe(S2C4N2)2]2(Na)2), and 4 consist of a doublet with a large quadrupole splitting in the case of 1 and 2 (3.278 and 3.149 mm s−1, respectively, at 293 K). Isomer shifts values of the nitrosylated compounds are lower (−0.171 for 2 vs. +0.177 for 1 at 293 K and +0.053 mm s−1 for 4 vs. +0.331 mm s−1 for 3 at 100 K).