# Why do nitrogen molecules not act as ligands in haemoglobin?

Nitrogen molecules $$(\ce{N2})$$ have lone pairs, which, as far as I know, is the property of oxygen molecules $$(\ce{O2})$$ that allows them to act as ligands bonding to iron in haemoglobin in the blood. Why then is atmospheric nitrogen unable to act as a ligand and form dative bonds to iron in the blood as oxygen is able to?