Jahn-Teller effect
= Jahn-Teller effect
{c}
The <Jahn-Teller effect> is an instability of a nonlinear molecular arrangement with an orbitally degenerate electronic ground state toward a symmetry-lowering distortion. An octahedral high-<spin> $d^4$ ion has unequal occupation of its $e_g$ orbitals and often undergoes tetragonal elongation.