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 56 FeN and N 56 FeN 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 Fe 2 N 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.