Raman and infrared spectroscopy of the oxo-bridged iron(III) complex, [Cl3Fe-O-FeCl3]-2 as a spectroscopic model for the oxo bridge in hemerythrin and ribonucleotide reductase

Vibrational spectroscopic data were collected on the salt [C5H6N]2[Cl3FeOFeCl3] . C5H5N, which has previously been structurally characterized by X-ray crystallography. The modes associated with the oxo bridge were identified by experiments on the 18O-containing species. Spectra for the mu-16O complex contain Raman bands at 870, 458, and 203 cm-1 that shift to 826, 440, and 198 cm-1 in the mu-18O complex. These are respectively assigned to the asymmetric, symmetric, and angle deformations of the bent Fe-O-Fe moiety. A normal mode vibration analysis based on a simple valence force field for the Fe-O-Fe portion of the molecule provides surprisingly good agreement with these experimental frequencies and their assignments. The vibrational data for this simple inorganic complex confirm the assignment of a resonance Raman band around 500 cm-1 in the oxygen-carrying protein hemerythrin and enzyme ribonucleotide reductase as the symmetric stretch of an oxo bridge between two iron(III) centers.