PUB - Publikationen an der Universität Bielefeld

The reaction of 2,6-bis(hydroxymethyl)-4-tert-butylphenoI (H3L) with [Fe(III)(acac(3)] in acetonitrile in the presence of NEt3 yields [Fe(III)(4)(HL)(6)(acac)(2)](HNEt3)(2).3CH(3)CN (1) or after subsequent addition of [NEt4]Cl [Fe(III)(4)(HL)(6)(acac)(2)](NEt4)(2) (2) as reddish-brown crystalline solids. The molecular structure of 1 was established by single crystal X-ray diffraction. The dianion of complex 1 contains an [Fe4O6](6+) core with two mu(3)-bridging benzylalcoholato ligands and four mu(2)-bridging benzylalcoholato ligands. This is the first structurally characterized example for a benzy1alcoholato ligand bound to an octahedrally coordinated iron ion. The core of 1 can be considered as two face-sharing cuboidal [Fe3O4](5+) units. Compound 2 has been examined by FTIR, UV-Vis-NIR-absorption, Fe-57 Mossbauer, and magnetochemical measurements. Compound 2 has an S-t = 0 ground state indicative of antiferromagnetic interactions between the high-spin Fe(III) metal ions. The spin topology resembles that of the known [Fe4O2](8+) core with a 'butterfly' disposition of the four iron ions. Fitting of the data to the appropriate spin-Hamiltonian yields exchange-coupling constants between the 'inner' ('body') iron ions of J(bb) = - 10.0 +/- 0.1 cm(-1) and between the 'inner' iron ions and 'outer' ('wing-tip') iron ions of J(wb) = - 6.2 +/- 1.0 cm(-1). The differences of the spectroscopic and magnetochemical properties between the [Fe4O6](6+) core and the [Fe4O2](8+) core with an inversion of the superexchange pathways are discussed. (C) 2002 Elsevier Science B.V. All rights reserved.