EHMO studies of N₂ and C₂H₂ coordination-activation led to the conclusion that the iron-molybdenum cofactor of nitrogenase might be able to give a special treat to its special substrate, i. e. N≡N. The exogenous substrates except N₂ are apparently not to get into the cage of the active-center and / or to manoeuvre as freely as N≡N inside the cage with the proposed structural settings.