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

Using a supramolecular approach a class of compounds containing the [(H2O)(5)Fe-O-Fe(H2O)(5)](4+) core, viz. [(H2O)(5)Fe-O-Fe(OH2)(5)](NO3)(4).(18-crown-6)(2), (1), [(H2O)(5) Fe-O-Fe(OH2)(5)](ClO4)(4).(18-crown-6)(2).2H(2)O (2) and [(H2O)(5)Fe-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 Mossbauer spectroscopy, X-ray crystallography and magnetic susceptibility. The X-ray structures reveal the crown ethers, anions and the [(H2O)(5)Fe-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.