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Article

Square Planar vs Tetrahedral Geometry in Four Coordinate Iron(II) Complexes

Supporting Info

Eric J. Hawrelak,^†^‡ Wesley H. Bernskoetter,^† Emil Lobkovsky,^† Gordon T. Yee,^§ Eckhard Bill, and Paul J. Chirik*^†

Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0212, and Max-Planck-Institute for Bioinorganic Chemistry, Stiftstrasse 34-36, D-45470 Mlheim an der Ruhr, Germany

Inorg. Chem., 2005, 44 (9), pp 3103–3111

DOI: 10.1021/ic048202+

Publication Date (Web): March 29, 2005

†

Cornell University.

‡

Current address: Department of Chemistry, 237A Hartline Science Center, Bloomsburg University, Bloomsburg, PA 17815.

Virginia Polytechnic Institute and State University.

Max-Planck-Institute for Bioinorganic Chemistry.

Author to whom correspondence should be addressed. E-mail: pc92@ cornell.edu.

Abstract

The geometric preferences of a family of four coordinate, iron(II) d⁶ complexes of the general form L₂FeX₂ have been systematically evaluated. Treatment of Fe₂(Mes)₄ (Mes = 2,4,6-Me₃C₆H₂) with monodentate phosphine and phosphite ligands furnished square planar trans-P₂Fe(Mes)₂ derivatives. Identification of the geometry has been accomplished by a combination of solution and solid-state magnetometry and, in two cases (P = PMe₃, PEt₂Ph), X-ray diffraction. In contrast, both tetrahedral and square planar coordination has been observed upon complexation of chelating phosphine ligands. A combination of crystallographic and magnetic susceptibility data for (depe)Fe(Mes)₂ (depe = 1,2-bis(diethylphosphino)ethane) established a tetrahedral molecular geometry whereas SQUID magnetometry and Mössbauer spectroscopy on samples of (dppe)Fe(Mes)₂ (dppe = 1,2-bis(diphenylphosphino)ethane) indicated a planar molecule. When dissolved in chlorinated solvents, the latter compound promotes chlorine atom abstraction, forming tetrahedral (dppe)Fe(Mes)Cl and (dppe)FeCl₂. Ligand substitution reactions have been studied for both structural types and are rapid on the NMR time scale at ambient temperature.