Generally, the calculations of the nearly linear Fe-N-O geometries can be explained by understanding the electronic structure of the linear Fe-C=O geometry as outlined by . These take into account that Fe(III)-NO and Fe(II)-CO systems are isoelectronic to each other. In the case of CO, the πg* is empty and remains at high energy upon binding of Fe(II) to CO, and the linear geometry of Fe-C-O allows further interactions between the orbitals dxz/dyz and πg* . Furthermore, this geometry guarantees a stronger σ-bonding between Fe and CO.