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 + N-2 system show that laser-ablated Fe atoms react with nitrogen atoms and molecules to give the FeN and NFeN molecules and Fe(N-2)(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 (FeN)-Fe-56 and (NFeN)-Fe-56 molecules in solid nitrogen. The NFeN molecule is bent with valence angle 115 +/- 5 degrees 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(N-2) and (Fe-2)(N-2), respectively, agree very well with earlier CASSCF frequency calculations and approach the frequency of N-2 adsorbed on Fe(111). Structure and frequency calculations were done using density functional theory to support the identification of these new Fe(N-2)(x) molecular complexes.