20 1 Crystal-Field Theory – g Jahn-Teller Effect SI

When the numbers of electrons in the two eg orbitals are different, large John-Teller effect is observed. When the numbers of electrons in the three t2g orbitals are not exactly same, small John-Teller effect is observed. The reason is the two eg orbitals point directly to the ligands and thus are more severely affected by the elongation of the M-L bond, whereas the three t2g orbitals do NOT directly point to the ligands and thus are less affected by the elongation of the M-L ligands.

The elongation of the 2 M-L bonds in the z direction lowers the energy of the dz2, dxz, dyz orbitals. The elongation of the 4 M-L bonds in the x and y directions lowers the energy of the dx2-y2 and dxy orbitals.