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Synthesis, Structure, and Spectroscopic Properties of a Dinuclear Fe III ( μ 2 ‐O)Fe III Complex Using a Strongly Electron‐Donating Ligand: Implications for the Generation of New High‐Valent Species
Author(s) -
Glaser Thorsten,
Pawelke Roland H.,
Heidemeier Maik
Publication year - 2003
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.200300222
Subject(s) - crystallography , chemistry , quadrupole splitting , intramolecular force , magnetic susceptibility , covalent bond , ligand (biochemistry) , mössbauer spectroscopy , electronic structure , absorption spectroscopy , crystal structure , antiferromagnetism , electron paramagnetic resonance , stereochemistry , nuclear magnetic resonance , computational chemistry , physics , biochemistry , receptor , organic chemistry , quantum mechanics , condensed matter physics
Abstract The dinuclear complex [LFe III ( μ 2 ‐O)Fe III L] ( 1 ) (H 2 L = ‐ 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 N 2 O 2 donor set of L 2— 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 Fe III high spin centers ( S i = 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 Fe III sites. The electrochemical analysis reveals two oxidative electron‐transfer waves at E 1/2 = +0.28 V and E 1/2 = +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 L 2— to stabilize high‐valent dinuclear iron species.