XAS characterization of a nitridoiron(IV) complex with a very short Fe-N bond

X-ray absorption spectroscopy has been used to characterize the novel nitridoiron(IV) units in two [PhBP^R₃]Fe(N) complexes (R = iPr and CyCH₂) and obtain direct spectroscopic evidence for a very short Fe-N distance. The distance of 1.51-1.55 Å reflects the presence of an Fe≡N triple bond in accord with the observed Fe≡N vibration observed for one of these species (ν_FeN = 1034 cm^-1). This highly covalent bonding interaction results in the appearance of an unusually intense pre-edge peak, whose estimated area of 100(20) units is much larger than those of the related tetrahedral complexes with Fe ^I-N₂-Fe^I, Fe^II-NPh₂, and Fe^III≡NAd motifs, and those of recently described six-coordinate Fe^V≡N and Fe^VI≡N complexes. The observation that the Fe^IV-N distances of two [PhBP^R ₃]Fe(N) complexes are shorter than the Fe^IV-O bond lengths of oxoiron(IV) complexes may be rationalized on the basis of the greater π basicity of the nitrido ligand than the oxo ligand and a lower metal coordination number for the Fe(N) complex.