Electronic Configurations and the Effect of Peripheral Substituents of (Nitrosyl)iron Corroles

There have been debates on the electronic configurations of (nitrosyl)iron corroles for decades. In this work, pentacoordinate [Fe(TPC)(NO)], [Fe(TTC)(NO)], and [Fe(TpFC)(NO)] with different para-substituted phenyl groups (TPC, TTC, and TpFC = tris(phenyl, 4-tolyl, or 4-fluorophenyl)corrole, respectively) have been isolated and investigated by various techniques including single-crystal X-ray diffraction, UV-vis spectroscopy, cyclic voltammetry, Fourier transform infrared, NMR, and absorption fine structure spectroscopy. Multitemperature and high-magnetic-field (3, 6, and 9 T) Mössbauer spectroscopy was also applied on all three complexes, which determined the S = 0 diamagnetic states, consistent with the magnetic susceptibility and electron paramagnetic resonance measurements. Density functional theory predictions by different functionals were compared, and the new calculation strategy, which gave remarkable agreement of the experimental Mössbauer parameters (ΔE_Q and δ), allowed further assignment on the electronic configuration of {FeNO}⁶-(corrole^3-) with antiferromagnetically coupled (S = ¹/₂, Fe^III) and (S = ¹/₂, NO). Correlated sequences between the electronic donating/withdrawing capability of para substituents and the reduction/oxidation potentials, metal out-of-plane displacements (Δ₄ and Δ₂₃), and Mössbauer parameters (V and ΔE_Q) were also established, which suggests the strong effects of peripheral substituents.