title: Iron-Semiquinone, Semiquinone-Semiquinone, and Iron-Iron Magnetic Exchange in Monomeric and Dimeric Ferric Complexes Containing the 3,6-Di-tert-butyl-1,2-semiquinonate Ligand.
abstract: Fe(3,6-DBSQ)(3) has been prepared by reacting 3,6-di-tert-butyl-1,2-benzoquinone with Fe(CO)(5). The complex has been characterized structurally [orthorhombic, Pbca, a = 18.277(5) Å, b = 11.634(3) Å, c = 39.903(10) Å, V = 8485(4) Å(3), Z = 8, R = 0.063], electrochemically, and magnetically. Ligand-based redox couples are observed in electrochemical experiments that consist of reversible or quasireversible Cat/SQ steps at negative potentials and irreversible SQ/BQ oxidations at positive potentials. Magnetic measurements show temperature dependence that arises from antiferromagnetic exchange. Data have been fit to an expression that includes the effects of both Fe-SQ and SQ-SQ exchange with the result that J(SQ-SQ) is larger in magnitude than J(Fe-SQ). In methanol, the complex undergoes solvolysis to form [Fe(3,6-DBSQ)(2)(&mgr;-OMe)](2). Structural characterization [triclinic, P&onemacr;, a = 11.441(2) Å, b = 11.514(2) Å, c = 14.552(2) Å, alpha = 67.86(1) degrees, beta = 70.51(1) degrees, gamma = 72.79(1) degrees, V = 1641.8(5) Å(3), Z = 1, R = 0.048] has shown that the molecule is a centrosymmetric dimer with no close intermolecular contacts. The temperature dependence of magnetic measurements has been fit to a model consisting of two interacting S = (3)/(2) centers that arise from strong Fe-SQ exchange with J(Fe-Fe) = -22.4 cm(-1).
authors.affiliation: Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309.
authors.forename: Attia S.
authors.initials: AS
authors.lastname: Attia
authors.forename: Brenda J.
authors.initials: BJ
authors.lastname: Conklin
authors.forename: Christopher W.
authors.initials: CW
authors.lastname: Lange
authors.forename: Cortlandt G.
authors.initials: CG
authors.lastname: Pierpont