Theoretical calculations for catalytic activation of N₂ on a modelled iron adsorption site

MINDO/SR-UHF calculations were done on [FeN₂]^q(q = 1, 0 or -1 ) systems in end-on and side-on geometries in order to study the electronic and geometric factors that affect the adsorption of N₂ on iron adsorption sites. All systems studied in the end-on geometry were found to be stable. The adsorption energy of N₂ increases in the order. [FeN₂]^- > [FeN₂]^o > [FeN₂]⁺. The N-N bond is activated by the electronic transfer from Fe^q to N₂ in all cases, this effect is particularly large for the [FeN₂]^- system. Side-on interaction leads to thermodynamically unstable systems with a highly activated N₂ molecule. Distortion energy curves show high energy barriers in going from end-on to side-on geometries and very low barriers for the inverse process.