Utilization of crown ethers to stabilize the dinuclear µ-oxo bridged iron(III) aqua ion, [(H2O)5Fe(µ-O)Fe(OH2)5]4+

Abstract

Using a supramolecular approach a class of compounds containing the [(H2O)5Fe–O–Fe(H2O)5]4+ core, viz. [(H2O)5Fe–O–Fe(OH2)5](NO3)4·(18-crown-6)2, (1), [(H2O)5Fe–O–Fe(OH2)5](ClO4)4·(18-crown-6)2·2H2O (2) and [(H2O)5Fe–O–Fe(OH2)5](NO3)10[Fe(OH2)6]2(15-crown-5)4·(H2O)6, (3), has been prepared and characterized. These three complexes were characterized by electronic, infrared, Raman and Mössbauer spectroscopy, X-ray crystallography and magnetic susceptibility. The X-ray structures reveal the crown ethers, anions and the [(H2O)5Fe–O–Fe(H2O)5]4+ cores are all involved in extensive hydrogen bonding, thus stabilizing the unprecedented (in the solid state) dimeric cores. Magnetic susceptibility measurements show a strong antiferromagnetic coupling in each complex that is consistent with current radial and angular overlap descriptions of exchange coupling in mono-oxo bridged dinuclear Fe(III) complexes.