Synthesis, Structural, Redox and Mössbauer Characterization of Four‐Electron‐Oxidized Tetrakis(cyclohexyl)iron(II)porphodimethene with Different Axial Ligations

Monocationic Fe II porphodimethene complexes, [L ΔΔ Fe–X][Y] { 1 , X = I – and Y = I 3 – ; 2 , X = Br – and Y = [Fe III Br 4 ] – ; L ΔΔ = tetrakis(cyclohexyl)porphodimethene}, were achieved by induced electron‐transfer reactions between the square‐planar, intermediate‐spin, iron(III)porphyrinogen complex [Et 4 N][LFe III ] [L = tetrakis(cyclohexyl)porphyrinogen tetraanion] and different oxidants. Single‐crystal X‐ray diffraction analysis reveals that 1 and 2 have a square‐pyramidal geometry in which the iodide and bromide ligands occupy the axial position, respectively. Compound 1 exhibits an extended two‐dimensional solid‐state structure that comprises porphodimethene cation and triiodide anion chain columns in a 1:1 ratio, which are packed alternately. Electrochemical assessment with cyclic voltammetry reveals reversibly accessible Fe II/III oxidation states; however, the redox potential is nearly one volt more positive than that for a typical heme cofactor, which suggests the highly oxidizing nature of the tetrapyrrole framework in the four–electron‐oxidized L ΔΔ moiety. In addition, definitive experimental oxidation state and spin state assignments for the intermediate‐spin [Et 4 N][LFe III ] and high‐spin Fe II states of 1 and 2 were afforded by Mössbauer characterization.