Synthesis, Structure, and Spectroscopic Properties of a Dinuclear FeIII(μ2-O)FeIII Complex Using a Strongly Electron-Donating Ligand: Implications for the Generation of New High-Valent Species

The dinuclear complex [LFeIII(μ2‐O)FeIIIL] (1) (H2L = ‐N, N′‐dimethyl‐N, N′‐bis(3, 5‐di‐tert‐butyl‐2‐hydroxybenzyl)‐1, 2diaminoethane) has been synthesized and structurally characterized by elemental analysis, MALDI‐TOF MS, FTIR, and single crystal X‐ray diffraction. The electronic structure has been investigated by means of electronic absorption, electrochemistry, Mössbauer spectroscopy, and variable‐temperature magnetic susceptibility measurements. The iron atoms are five‐coordinated in an idealized square‐pyramidal coordination environment. The N2O2 donor set of L2— forms the equatorial plane while the bridging oxo‐ligand is in the axial position forming a linear Fe—O—Fe unit. The Mössbauer spectrum at 80 K consists of one quadrupole doublet with an isomer shift of 0.45 mm s—1 and a quadrupole splitting of 1.22 mm s—1. The low isomer shift is indicative of highly covalent metal‐ligand bonds resulting in electron‐rich FeIII high spin centers (Si = 5/2). Variable‐temperature magnetic susceptibility measurement reveals an intramolecular antiferromagnetic coupling (J = —96 cm—1). Strong LMCT transitions in the vis‐region of the absorption spectrum are in accordance to the highly covalent nature of the FeIII sites. The electrochemical analysis reveals two oxidative electron‐transfer waves at E1/2 = +0.28 V and E1/2 = +0.45 V vs Fc+/Fc. These experimental data provide insight into the electronic structure of the dinuclear complex and into the ability of the strongly electron‐donating ligand L2— to stabilize high‐valent dinuclear iron species. Synthese, Struktur und spektroskopische Eigenschaften eines dinuklearen FeIII(μ2‐O)FeIII Komplexes mit einem stark elektrondonierenden Liganden: Implikationen zur Darstellung neuer hochvalenter Spezies Der dinukleare Komplex [LFeIII(μ2‐O)FeIIIL] (1) (H2L = N, N′‐Dimethyl‐N, N′‐bis(3, 5‐di‐tert‐butyl‐2‐hydroxybenzyl)‐1, 2‐diaminoethan) wurde dargestellt und durch Elementaranalyse, MALDI‐TOF MS, FTIR und Einkristall‐Röntgenbeugung strukturell charakterisiert. Die Elektronenstruktur wurde mittels Elektronenabsorptionsspektroskopie, Elektrochemie, Mößbauer‐Spektroskopie und temperaturabhängigen magnetischen Suszeptibilitätsmessungen untersucht. Die Eisenatome sind in einer idealisierten quadratisch‐pyramidalen Koordinationsumgebung fünffach koordiniert. Der N2O2‐Donorsatz des Liganden L2— bildet die äquatoriale Ebene, während der verbrückende Oxo‐Ligand die axiale Position mit einer linearen Fe—O—Fe Einheit einnimmt. Das Möß