Fe(III)-hydroperoxo and peroxo complexes with aminopyridyl ligands and the Resonance Raman spectroscopic identification of the Fe-O and O-O stretching modes

Nonheme Fe(III)-hydroperoxo and Fe(III)-peroxo complexes with aminopyridyl-type ligands have been prepared and characterized by UV/Vis, EPR, mass and Resonance Raman (RR) spectroscopy. The Fe(III)(OOH) species are low-spin and exhibit a deep purple color due to the ligand-to-metal charge transfer (LMCT) hand centered at ca. 550 nm. The RR spectra of the Fe(III)(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, Fe(III)(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 Fe(III)(O₂) complex.