Bis(α-diimine)iron Complexes: Electronic Structure Determination by Spectroscopy and Broken Symmetry Density Functional Theoretical Calculations

• Published in: Inorganic chemistry Vol. 47; no. 11; pp. 4579 - 4590
• Main Authors: Muresan, Nicoleta, Lu, Connie C, Ghosh, Meenakshi, Peters, Jonas C, Abe, Megumi, Henling, Lawrence M, Weyhermöller, Thomas, Bill, Eckhard, Wieghardt, Karl
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 02.06.2008
• Subjects: Chlorides; Crystallography, X-Ray; Density; Electronic structure; Electrons; Ground state; Imines - chemistry; Iron - chemistry; Ligands; Magnetics; Mathematical analysis; Mossbauer spectroscopy; Organometallic Compounds - chemistry; Quantum Theory; Radicals; Spectrum Analysis - methods; Temperature
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic7022693

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 (S t = 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) (S Fe = 2). Intramolecular antiferromagnetic coupling between the π radical ligands (S rad = 1/2) and the ferrous ion (S Fe = 2) yields the observed S t = 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)FeCl2 complexes (S t = 2) are shown to contain a neutral α-diimine ligand, a high spin ferrous ion, and two chloride ligands.