Bis(α-diimine)iron complexes: Electronic structure determination by spectroscopy and broken symmetry density functional theoretical calculations

Nicoleta Muresan, Connie C. Lu, Meenakshi Ghosh, Jonas C. Peters, Megumi Abe, Lawrence M. Henling, Thomas Weyhermöller, Eckhard Bill, Karl Wieghardt

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74 Scopus citations

Abstract

The electronic structure of a family comprising tetrahedral (α-diimine)iron dichloride, and tetrahedral bis(α-diimine)iron compounds has been investigated by Mössbauer spectroscopy, magnetic susceptibility measurements, and X-ray crystallography. In addition, broken-symmetry density functional theoretical (B3LYP) calculations have been performed. A detailed understanding of the electronic structure of these complexes has been obtained. A paramagnetic (St = 2), tetrahedral complex [FeII(4L)2], where (4L) 1- represents the diamagnetic monoanion N-tert-butylquinolinylamide, has been synthesized and characterized to serve as a benchmark for a Werner-type complex containing a tetrahedral FeIIN4 geometry and a single high-spin ferrous ion. In contrast to the most commonly used description of the electronic structure of bis(α-diimine)iron(0) complexes as low-valent iron(0) species with two neutral α-diimine ligands, it is established here that they are, in fact, complexes containing two (α-diiminato)1-• π radical monoanions and a high-spin ferrous ion (in tetrahedral N4 geometry) (SFe = 2). Intramolecular antiferromagnetic coupling between the π radical ligands (Srad = 1/2) and the ferrous ion (SFe = 2) yields the observed St = 1 ground state. The study confirms that α-diimines are redox noninnocent ligands with an energetically low-lying antibonding π* lowest unoccupied molecular orbital which can accept one or two electrons from a transition metal ion. The (α-diimine)FeCl 2 complexes (St = 2) are shown to contain a neutral α-diimine ligand, a high spin ferrous ion, and two chloride ligands.

Original languageEnglish (US)
Pages (from-to)4579-4590
Number of pages12
JournalInorganic chemistry
Volume47
Issue number11
DOIs
StatePublished - Jun 2 2008

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