Abstract
We report the syntheses, structural, Mossbauer, magnetic, and redox characterization of a series of mu-oxido-bridged diiron(III) complexes in a set of 13-membered amide-based macrocyclic ligands that contain electron-donating and -withdrawing substituents (-H, -Cl, and -CH3) on the ligand periphery. For all three complexes, the Mossbauer spectra indicate that two iron sites are indistinguishable, a fact that is well supported by X-ray crystallographic results. The three complexes exhibit almost identical isomer shifts but distinctively different quadruple splitting values. The variable-temperature magnetic susceptibility measurements show that the unsupported single mu-oxido group mediates a strong antiferromagnetic coupling between two Fe-III ions. The three diiron complexes show quite different magnetic coupling (J = 191, 194, and 230 cm(-1), respectively; H-iso = JS(1)center dot S-2) that has been related to the structural differences. We also show that the electron-donating and -withdrawing substituents present on the ligands influence the redox properties.