Tetrahedral crystal field splitting (${\Delta }_t$)

In the ideal tetrahedral point-charge model, the five metal d orbitals split into a lower twofold $e$ set and an upper threefold $t_2$ set. Relative to their weighted barycentre their energies are $-3{\Delta }_t/5$ and $+2{\Delta }_t/5$, where ${\Delta }_t>0$ is the separation. For occupancies $e^{n_e}{t}_2^{n_t}$, the crystal field stabilization energy is $(-0.6n_e+0.4n_t){\Delta }_t$. Under weak-field high-spin filling it is $-0.6{\Delta }_t$, $-1.2{\Delta }_t$, $-0.8{\Delta }_t$ and zero for $d^6,d^7,d^8,d^{10}$ respectively. Shorter metal–ligand distances generally increase the splitting, so orbital filling can superimpose nonmonotonic bond-length changes on an ionic-size trend. The model alone does not determine an absolute bond length.