# 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?

• N2 is even worse as ligand then oxygen, its complexes are rare. Mar 21 '18 at 21:20
• It can, at least at high pressure, see e.g. ncbi.nlm.nih.gov/pubmed/3417671 Mar 22 '18 at 7:49
• @Mithoron Okay, but why is N2 a worse ligand than O2?
– R.M.
Mar 22 '18 at 21:43
• chemistry.stackexchange.com/questions/118773/… I have a similar question but still no answer Aug 10 '19 at 20:02
• Jun 25 '20 at 5:28