In the quintet state the antibonding α-e * g (where α denotes spin up) orbitals are populated, therefore, the molecule is expanded: the calculations show a 10% increase in the Fe-N bond lengths with respect to the singlet ground state, see Table 7 (and Table ). Experimental values are only available for the parent compound, which agree well with the calculations. Although the structural parameters vary slightly from complex to complex, but they do not show a clear correlation with the substituents. Below about R + =-0.5, the difference in Fe-N bond lengths becomes significantly smaller.