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

Abstract

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.

A Dinucleating Ligand System with Varying Terminal Donors to Mimic Diiron Active Sites

“…[(hilde Me 2 ){Fe(μ-O)Fe}] and the μ-oxo-bridged diferric complexes with our mononucleating analogues of H 4 hilde Me 2 can be oxidized at relatively low potentials. [45,62,64,65] Spectroscopic characterizations of the oxidized species reveal, that the oxidations are ligand-centered leading to mono-and diphenoxyl radical complexes. [62,65] The latter accumulating the same number of oxidation equivalents as intermediate Q from sMMO.…”

“…Reactions of the phenolate containing ligand H 4 hilde with a Fe III source under basic conditions in an alcoholic solvent provide the complex [(hilde ){Fe( μ ‐O)Fe}] with the Fe III ions in a five‐coordinate trigonal‐bipyramidal environment (Figure 1a) [45] . With related mononucleating ligands, [62–65] μ ‐oxo‐bridged diferric complexes with five‐coordinate square‐pyramidal coordination environment were obtained. The reaction of the ligand H 4 julia with an Fe III source is best performed in aqueous solution under slightly basic conditions and provides the μ ‐oxo‐bridged complex [(julia){Fe(OH 2 )( μ ‐O)Fe(OH 2 )}] (Figure 1b) [46] .…”

Mononuclear iron(III) complexes derived from tridentate ligands containing non‐innocent phenolato donors: Self‐activated nuclease, protease, and phenoxazinone synthase activity studies

“…The lowest energy absorptions band in the region near 500 nm is probably due to charge–transfer transition between phenolate (p π ) → iron(III) (d π* ) orbitals. [ 57–59 ] All the complexes showed characteristic peak [M–ClO 4 ] + in positive ion mode (shown in Figures S14–S16).…”

A binuclear iron(III) Schiff base complex doubly bridged by hydroxyl groups: Synthesis, structure, and characterization

“…Meanwhile, iron is an essential trace element, and is the main component of hemoglobin in human blood. Because the iron(III) ion has the most self spin single electrons, the design, synthesis, and characterization of iron complexes with Schiff base ligands play the vital role in coordination chemistry due to the importance as synthetic models for the functional materials [4][5][6][7]. In addition, as we all know, the pseudohalide ions, N 3 [8], diamine [9], and oxygen atom [10] have been well exploited for their ability to bridge paramagnetic moieties into dimers, clusters, and even polymers.…”