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

  • Muresan N
  • Lu C
  • Ghosh M
 et al. 
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Abstract

The electronic structure of a family comprising tetrahedral (alpha-diimine)iron dichloride, and tetrahedral bis(alpha-diimine)iron compounds has been investigated by Mossbauer 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 (S-t = 2), tetrahedral complex [Fe-II(L-4)(2)], where (L-4)(1-) represents the diamagnetic monoanion N-tert-butylquinolinylamide, has been synthesized and characterized to serve as a benchmark for a Wemer-type complex containing a tetrahedral (FeN4)-N-II geometry and a single high-spin ferrous ion. In contrast to the most commonly used description of the electronic structure of bis(alpha-diimine)iron(0) complexes as low-valent iron(0) species with two neutral alpha-diimine! ligands, it is established here that they are, in fact, complexes containing two (alpha-diiminato)(1-center dot) pi radical monoanions and a high-spin ferrous ion (in tetrahedral N-4 geometry) (S-Fe = 2). Intramolecular antiferromagnetic coupling between the pi radical ligands (S-rad = 1/2) and the ferrous ion (SFe = 2) yields the observed S-t = 1 ground state. The study confirms that alpha-diimines are redox noninnocent ligands with an energetically low-lying antibonding pi* lowest unoccupied molecular orbital which can accept one or two electrons from a transition metal ion. The (alpha-diimine)FeCl2 complexes (S-t = 2) are shown to contain a neutral alpha-diimine ligand, a high spin ferrous ion, and two chloride ligands.

Author-supplied keywords

  • alpha-diimine ligands
  • diradical character
  • gaussian-basis sets
  • iron-sulfur clusters
  • mossbauer-spectra
  • n-substituents
  • planar nickel-complexes
  • square-planar
  • transfer radical polymerization
  • transition-metal dimers

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Authors

  • N Muresan

  • C C Lu

  • M Ghosh

  • J C Peters

  • M Abe

  • L M Henling

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