AbstractThe heats of formation of octahedrally coordinated complexes of O‐containing ligands follow a relationship, proposed earlier\documentclass{article}\pagestyle{empty}\begin{document}$$ -{\rm U = C}_{\rm L} + {\rm I - n}_{\rm e} \Delta _{\rm L}$$\end{document}while those of N‐containing ligands follow a more involved equation\documentclass{article}\pagestyle{empty}\begin{document}$$ -{\rm U = C}_{\rm L} + {\rm I + n}_{\rm t} \gamma _{\rm L} - {\rm n}_e \Delta _{\rm L} $$\end{document}where I‐the ionization potential (I1+ I2of the atom, CL, ΔLand γLare constants dependent on the ligand, while ntand neare the number of 3d‐electrons in the t2gand the eg‐antibonding orbitals. For O‐ligands, as for those ligands discussed previously ΔL∼ Δs(spectroscopic ligand field splitting factor), while for N‐ligands, (ΔL+ γL) ∼ Δs. It is proposed that γLrepresents the depression in energy of the t2g‐levels by acceptor π‐bonding connected with a 3p‐orbital of atomic N: it is numerically equal to 6 kcal/at for a central ion with an environment of 6 N‐atoms.The ΔLand CL‐values for O‐ and N‐containing ligands appear almost equal, suggesting t