Mixed-valence dinuclear iron complexes with a nonadentate polypyridine ligand: high-spin iron(II)–low-spin iron(III)

Abstract

Dinuclear iron(II, III) complexes [Fe₂L(O₂CMe)][O₂CMe]X₂ with a nonadentate ligand HL, i.e. 4-methyl-2,6-bis[N-(2-pyridylmethyl)-N-(2-pyridylmethyleneaminoethyl)aminomethyl]phenol, and X = PF₆^–(1) or BPh₄^–(2) have been prepared. Their Mössbauer spectra consist of two quadrupole doublets due to high-spin iron(II) and low-spin iron(III). The magnetic susceptibilities are consistent with this. Cyclic voltammograms in dried acetonitrile showed a quasi-reversible redox couple with E₁=–0.07 V and an irreversible redox couple with E₂= 0.58 V vs. saturated calomel electrode for 1, corresponding to a comproportionation constant of 1.0 × 10¹². No visible or near-infrared bands due to intervalence electron transitions between iron-(II) and -(III) were observed.