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

摘要

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) Angstrom, b = 11.634(3) Angstrom, c = 39.903(10) Angstrom, V = 8485(4) Angstrom(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)(mu-OMe)](2). Structural characterization [triclinic, , a = 11.441(2) Angstrom, b = 11.514(2) Angstrom, c = 14.552(2) Angstrom, alpha = 67.86(1)degrees, beta = 70.51(1)degrees, gamma = 72.79(1)degrees, V = 1641.8(5) Angstrom(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). [References: 18]