Ferrocenium µ-oxo-bis[tribromoferrate(III)], a product of reaction of ferrocene with iron(III) bromide

The µ-oxo anion [(FeBr3)2O]2– has been prepared as its ferrocenium salt. The crystal and molecular structure [orthorhombic, space group Cmc2, a= 13.739(2), b= 14.721(3), c= 14.302(2)A] has been determined. The anion consists of two corner-sharing FeBr3O tetrahedra with parameters similar to those of the chloro-analogue. The cations are ferroceniums with eclipsed cyclopentadienyl rings. The magnetic susceptibility over a range of temperature is that expected for an intramolecular antiferromagnet. Both the cation and anion resonances in the Mossbauer spectrum are consistent with the structure as is the infrared spectrum. The crystal and molecular structure [orthorhombic, space group Pmcn, a= 9.036(3), b= 12.137(2), c= 14.192(2)A] of [Fe(η-C5H5)2][FeBr4] has also been determined. This consists of a perfectly tetrahedral anion and a ferrocenium with eclipsed cyclopentadienyl rings.