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, Mossbauer and variable-temperature susceptibility establishes that I 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 Angstrom (4). They differ by the position of the nu(NO) 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 Mossbauer 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). (C) 2002 Elsevier Science B.V. All rights reserved.