title: Structure and magnetic properties of a non-heme diiron complex singly bridged by a hydroxo group.
abstract: The synthesis of the first singly bridged non-heme diiron complex with a mu-hydroxo bridging ligand, [{(salten)Fe}2(OH)][B(C6H5)4].(CH3CN)x.(H2O)y (1) [H2salten = 4-azaheptane-1,7-bis(salicylideneiminate)], is reported. The complex has been characterized with X-ray crystallography, FTIR, magnetic susceptibility measurements, and Mössbauer spectroscopy. The data have been compared with the results of DFT calculations on both 1 and a model with an unsupported mu-oxo bridge (2) to verify the formulation of the complex as a mu-hydroxo-bridged species. The X-ray structure [Fe-O(H) = 1.997(1) A and Fe-O(H)-Fe = 159 degrees ] is consistent with the DFT-optimized geometry of 1 [Fe-O(H) = 2.02 A and Fe-O(H)-Fe = 151 degrees ]; the Fe-O(H) distance in 1 is about 0.2 A longer than the Fe-O separations in the optimized geometry of 2 (1.84 A) and in the crystallographic structures of diiron(III) compounds with unsupported mu-oxo bridges (1.77-1.81 A). The formulation of 1 as a hydroxo-bridged compound is also supported by the presence of an O-H stretch band in the FTIR spectrum of the complex. The magnetic susceptibility measurements of 1 reveal antiferromagnetic exchange (J = 42 cm(-1) and H(ex) = JS(1).S(2)). Nearly the same J value is obtained by analyzing the temperature dependence of the Mössbauer spectra (J = 43 cm(-1); other parameters: delta = 0.49 mm s(-1), DeltaE(Q) = -0.97 mm s(-1), and eta = 0.45 at 4.2 K). The experimental J values and Mössbauer parameters agree very well with those obtained from DFT calculations for the mu-hydroxo-bridged compound (J = 46 cm(-1), delta = 0.48 mm s(-1), DeltaE(Q) = -1.09 mm s(-1), and eta = 0.35). The exchange coupling constant in 1 is distinctly different from the value J approximately 200 cm(-1) calculated for the optimized mu-oxo-bridged species, 2. The increased exchange-coupling in 2 arises primarily from a decrease in the Fe-O bond length.
authors.affiliation: Institut Lavoisier de Versailles, UMR-CNRS 8180, University of Versailles, 78035 Versailles Cedex, France.
authors.forename: Josseline
authors.initials: J
authors.lastname: Jullien
authors.forename: Gergely
authors.initials: G
authors.lastname: Juhász
authors.forename: Pierre
authors.initials: P
authors.lastname: Mialane
authors.forename: Eddy
authors.initials: E
authors.lastname: Dumas
authors.forename: Cédric R
authors.initials: CR
authors.lastname: Mayer
authors.forename: Jérôme
authors.initials: J
authors.lastname: Marrot
authors.forename: Eric
authors.initials: E
authors.lastname: Rivière
authors.forename: Emile L
authors.initials: EL
authors.lastname: Bominaar
authors.forename: Eckard
authors.initials: E
authors.lastname: Münck
authors.forename: Francis
authors.initials: F
authors.lastname: Sécheresse
mesh_terms: D003432:Cross-Linking Reagents / Q000737:chemistry*; D018360:Crystallography, X-Ray; D005290:Ferric Compounds / Q000737:chemistry*; D006418:Heme / Q000737:chemistry; D008280:Magnetics; D008958:Models, Molecular; D008968:Molecular Conformation; D013057:Spectrum Analysis
chemical_list: D003432:Cross-Linking Reagents; D005290:Ferric Compounds; D006418:Heme