Fe-O bond character of a µ-oxo-bridged iron phthalocyanine dimer investigated by O K-edge X-ray absorption spectroscopy.

A µ-oxo-bridged iron phthalocyanine dimer with eight peripheral -butyl substituents was investigated using soft X-ray absorption spectroscopy in its solid state. The O K-edge spectrum of the dimer showed a peak at 529.1 eV, corresponding to that of the Fe-µO-Fe core. The peak position is apparently at a lower energy than that of single-bonded oxygens, such as the oxygen of HO (>535 eV), and is almost comparable to the peak of oxytitanium phthalocyanine, whose oxygen atom has a double-bond character (530.6 eV), despite the fact that the µO-Fe bonds of the µ-oxo-bridged dimer have a single-bond character. DFT calculations clarified that the peak of the µ-oxo dimer at 529.1 eV is assignable to the excitation to the antibonding orbital localized in the µO-Fe unit.