title: Bis(alpha-diimine)iron complexes: electronic structure determination by spectroscopy and broken symmetry density functional theoretical calculations.
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 (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(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-* pi radical monoanions and a high-spin ferrous ion (in tetrahedral N4 geometry) (SFe=2). Intramolecular antiferromagnetic coupling between the pi radical ligands (Srad=1/2) and the ferrous ion (SFe=2) yields the observed St=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 (St=2) are shown to contain a neutral alpha-diimine ligand, a high spin ferrous ion, and two chloride ligands.
authors.affiliation: Max-Planck Institute for Bioinorganic Chemistry, Mülheim an der Ruhr, Germany.
authors.forename: Nicoleta
authors.initials: N
authors.lastname: Muresan
authors.forename: Connie C
authors.initials: CC
authors.lastname: Lu
authors.forename: Meenakshi
authors.initials: M
authors.lastname: Ghosh
authors.forename: Jonas C
authors.initials: JC
authors.lastname: Peters
authors.forename: Megumi
authors.initials: M
authors.lastname: Abe
authors.forename: Lawrence M
authors.initials: LM
authors.lastname: Henling
authors.forename: Thomas
authors.initials: T
authors.lastname: Weyhermöller
authors.forename: Eckhard
authors.initials: E
authors.lastname: Bill
authors.forename: Karl
authors.initials: K
authors.lastname: Wieghardt
mesh_terms: D018360:Crystallography, X-Ray; D004583:Electrons; D007097:Imines / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008280:Magnetics; D009942:Organometallic Compounds / Q000737:chemistry*; D011789:Quantum Theory; D013057:Spectrum Analysis / Q000379:methods*; D013696:Temperature
chemical_list: D007097:Imines; D009942:Organometallic Compounds; D007501:Iron