X-Ray absorption spectroscopy of iron-(II) and -(III) basket-handle porphyrins

X-Ray absorption near-edge structure and extended X-ray absorption fine structure spectroscopies have been used to characterize iron basket-handle porphyrins in various co-ordinations, stereochemistries and oxidation states. Attention is paid to the square-planar iron(II) complexes, a dioxygen adduct of FeII and a hydroxyiron(III) complex. The results are consistent with a FeII(O2) rather than a FeIII(O2–) formulation for the dioxygen adduct. A Fe–O distance of 1.94 Å was found in the hydroxo complex. The kinetics of oxidation of a dioxygen form to the hydroxo complex has been studied using a dispersive-mode X-ray absorption spectrometer (half-life ≈ 6 min).