Effect of π-acceptor and π-donor ligands on the energies of the ligand-field orbitals of three-coordinate iron compounds, as shown by computational studies.8,18,21,30 Interestingly, iron(I), iron(II), and iron(III) complexes can each have three electrons in the nearly degenerate yz/z2 orbitals. As in Figure 3, a non-standard choice of axes is used.