Molecular and electronic structure of six-coordinate low-spin oxo-bridged dimers formed by the interaction of (?-oxo)bis((phthalocyaninato)iron(III)) with nitrogen bases

Crystalline bisadducts of general formula [(N-base)PcFe]2O have been prepared by the interaction of (?-oxo)bis((phthalocyaninato)iron(III)) with vapors of liquid or liquid N-bases (pyridine, 4-methylpyridine, piperidine, 1-methylimidazole). Additional occluded molecules of the N-bases are also found present in the crystal lattice of these complexes. The molecular and electronic structure of the N-base adducts has been examined mainly on the basis of structural information and Mössbauer and magnetic susceptibility measurements. A six-coordinate structure and a low-spin (S = 1/2) electronic configuration is assigned to Fe(III) in these ?-oxo dimers, with a weak antiferromagnetic coupling between the iron pairs of the dimer. The stereochemistry and spin state on the iron centers contrast with those of the more common five-coordinate high-spin Fe(III) centers in other ?-oxo dimers.