Dinuclear oxido-bridged iron(III) complexes containing sulfato ligands

Abstract A new iron(III) sulfato complex [Fe 2 ( bpy ) 2 (H 2 O) 2 (µ-O)(µ-SO 4 ) 2 ]·3H 2 O has been prepared from iron(II) chloride by using potassium peroxydisulfate being the oxidation agent and the source of sulfato ligands as well. The compound has been characterized by infrared, Raman and Mössbauer spectroscopies. X-ray structure analysis confirmed the presence of the Fe(III)–O–Fe(III) core in the complex. Both sulfato groups are bonded in the form of bridged bis(monodentate) ligands. The coordination polyhedra about the central atoms are completed by 2,2′-bipyridine and water molecules, forming thus distorted octahedra. A thorough comparison of bonding parameters of all dinuclear oxido-bridged sulfato complexes of iron(III) that have been solved by X-ray structure analysis revealed several strong correlations between these parameters and bonding mode of sulfato ligands. The characteristic vibrational bands of the FeOFe group has been observed at 770 cm −1 (IR) for ν as (FeOFe) and at 513 cm −1 (IR) and 520 cm −1 (Raman) for ν s (FeOFe). The assignment of characteristic bands was corroborated by DFT calculation. The isomer shift values obtained in Mössbauer spectra indicate high-spin Fe 3+ , while the large quadrupole splitting is characteristic of oxygen bridged Fe 3+ ions.