Formation of dimethoxy bridged dinuclear iron(III) complex of pyridoxal Schiff base with iron-catalyzed oxidative C[sbnd]N bond cleavage – Structure, magnetic properties, and DFT calculations

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Mononuclear Fe(III) complex [FeL(N3)]·CH3OH, where L2– is the dianion of an unsymmetrical propyl-ethyl pentadentate Schiff base ligand condensed from pyridoxal and N-(2-aminoethyl)propane-1,3-diamine, and dinuclear Fe(III) complex [{FeL’}2(μ-OCH3)2]·2.5CH3OH·H2O, where L’2– is the dianion of tetradentate Schiff base ligand based on pyridoxal and ethylenediamine, have been synthesized and characterized by elemental analysis, X-ray structural analysis, FT-IR and mass spectrometry. Tetradentate pyridoxal Schiff base ligand L’2– of the dinuclear complex was generated in situ via iron-catalyzed oxidative CN bond cleavage of the pentadentate Schiff base. The coordination geometry around the iron(III) centers of the complexes can be described as adistorted octahedron. Magnetic investigations of [FeL(N3)]·CH3OH complex revealed that the octahedral Fe(III) center retains high-spin in the entire temperature range (2–300 K) and enabled the evaluation of the axial zero-field splitting (ZFS) parameter D = –1.78 cm−1, intermolecular exchange parameter zj́ = –1.35 cm−1 and temperature-independent paramagnetism χTIM = 0.00029 cm3mol−1. Magnetic investigations of [{FeL’}2(μ-OCH3)2]·2.5CH3OH·H2O showed that Fe(III) centers are coupled by a strong antiferromagnetic interaction (J = –94.5 cm−1). The experimental magnetic properties of the complexes were compared with the data obtained from the density functional theory (DFT) calculations.