Reactions of laser-ablated iron atoms with nitrogen atoms and molecules. Matrix infrared spectra and density functional calculations of novel iron nitride molecules

Matrix infrared spectra of the Fe + N₂ system show that laser-ablated Fe atoms react with nitrogen atoms and molecules to give the FeN and NFeN molecules and Fe(N₂)_x complexes. The iron nitride molecules FeN and NFeN were identified from nitrogen and iron isotopic shifts and splittings and density functional frequency calculations. Sharp 934.8 and 903.6 cm^-1 bands are assigned to the ⁵⁶FeN and N⁵⁶FeN molecules in solid nitrogen. The NFeN molecule is bent with valence angle 115 ± 5° as determined from iron and nitrogen isotopic shifts. Nitrogen-to-argon matrix shifts for FeN and NFeN are small. The cyclic Fe₂N molecule is observed at 779 and 719 cm^-1 in solid nitrogen. Strong bands in the 2200-2000 cm^-1 region are associated with end-bonded Fe(NN)_x complexes; the FeNN molecule absorbs at 2017.8 cm^-1 in solid argon. New absorptions at 1826.8 and 1683.7 cm^-1 in argon matrix experiments, identified as side-bonded Fe(N₂) and (Fe₂)(N₂), respectively, agree very well with earlier CASSCF frequency calculations and approach the frequency of N₂ adsorbed on Fe(111). Structure and frequency calculations were done using density functional theory to support the identification of these new Fe(N₂)_x molecular complexes.