Synthesis, molecular structure and magnetic properties of [Fe6(μ3-O)2(OPri)2(μ-OPri)6(O2CPh)2(μ-O2CPh)4]

The reaction of an Fe(III) oxo-benzoate species (1) with Al(OR)3 (R=Pri, Busec) yields the hexanuclear derivatives [Fe6(μ3-O)2(OR)8(O2CPh)6] (R=Pri (2); R=Busec (3)) which consist of planar Fe4(μ3-O)2 units, formed by two Fe3(μ3-O) groupings having common Fe(III) atoms, with further Fe(OR)4 entities, each attached by three bridging OR groups to Fe3(μ3-O) units, above and below the Fe4 plane. The OPri complex has an S=3 magnetic ground state and shows unusual temperature dependence of μeff below 60 K because of the complex series of low lying spin states generated by six high-spin Fe(III) centres undergoing antiferro- and ferromagnetic intracluster coupling. The Mössbauer spectrum at 81 K supports the presence of three inequivalent Fe sites in the molecule, as noted in the crystal structure.