(N/A) In tetrahedral coordination entities,the $d$-orbital splitting is inverted and is smaller compared to the octahedral field splitting.
The crystal field splitting energy,denoted as $\Delta_{t}$ (where the subscript $t$ stands for tetrahedral),for the same ligands and metal-ligand distances,is related to the octahedral splitting energy $\Delta_{0}$ by the expression: $\Delta_{t} = \frac{4}{9} \Delta_{0}$.
As a result,the orbital splitting energies are not sufficiently large to force electron pairing; therefore,low-spin configurations are rarely observed in tetrahedral complexes.
The '$g$' subscript (gerade) is used for octahedral and square planar complexes as they are centrosymmetric. Since tetrahedral complexes lack a center of symmetry,the '$g$' subscript is not used with their energy levels.
In the tetrahedral field,the energy of the two $e$ orbitals decreases by $\frac{3}{5} \Delta_{t}$,while the energy of the three $t_{2}$ orbitals increases by $\frac{2}{5} \Delta_{t}$ relative to the barycenter.