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

Fe(3,6-DBSQ)(3) has been prepared by reacting 3,6-di-tert-butyl-1,2-be nzoquinone with Fe(CO)(5). The complex has been characterized structur ally [orthorhombic, Pbca, a = 18.277(5) Angstrom, b = 11.634(3) Angstr om, 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 te mperature dependence that arises from antiferromagnetic exchange. Data have been fit to an expression that includes the effects of both Fe-S Q and SQ-SQ exchange with the result that J(SQ-SQ) is larger in magnit ude than J(Fe-SQ) In methanol, the complex undergoes solvolysis to for m [Fe(3,6-DBSQ)(2)(mu-OMe)](2). Structural characterization [triclinic , <P(1)over bar>, 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, g amma = 72.79(1)degrees, V = 1641.8(5) Angstrom(3), z = 1, R = 0.048] h as shown that the molecule is a centrosymmetric dimer with no close in termolecular contacts. The temperature dependence of magnetic measurem ents has been fit to a model consisting of two interacting S = 3/2 cen ters that arise from strong Fe-SQ exchange with J(Fe-Fe) = -22.4 cm(-1 ).