FeIII-Hydroperoxo and Peroxo Complexes with Aminopyridyl Ligands and the Resonance Raman Spectroscopic Identification of the Fe−O and O−O Stretching Modes

Nonheme FeIII-hydroperoxo and FeIII-peroxo complexes with aminopyridyl-type ligands have been prepared and characterized by UV/Vis, EPR, mass and Resonance Raman (RR) spectroscopy. The FeIII(OOH) species are low-spin and exhibit a deep purple color due to the ligand-to-metal charge transfer (LMCT) band centered at ca. 550 nm. The RR spectra of the FeIII(OOH) complexes display two bands at ca. 620 and 800 cm−1 that are assigned to the respective Fe−O and O−O stretching modes on the basis of the characteristic H/D and 16O/18O frequency shifts. Upon deprotonation, FeIII(O2) species are obtained which possess a high-spin configuration of nearly axial symmetry and a LMCT transition in the near infrared (ca. 750 nm). The frequencies of the Fe−O and O−O stretching modes at ca. 465 and 820 cm−1, as well as their respective 16O/18O shifts of −16 and −45 cm−1, indicate an η2 coordination geometry for the FeIII(O2) complex.