Answer:
K4[Cr(CN)6] and K4[Mn(CN)6]
Explanation:
The Jahn–Teller effect, sometimes also known as Jahn–Teller distortion, describes the geometrical distortion of molecules and ions that is associated with certain electron configurations. In Jahn Teller effect, more electrons occupy the lower orbital than the upper one, resulting in an overall lowering of the electronic energy. This distortion is typically observed among octahedral complexes where the two axial bonds can be shorter or longer than those of the equatorial bonds. In octahedral complexes, the Jahn–Teller effect is most pronounced when an odd number of electrons occupy the eg orbitals. This situation is most pronounced in complexes with the configurations d9 , low-spin d7 or high-spin d4. These configurations display a strong Jahn Teller effect. Jahn Teller may also be observed if there is a degeneracy due to the electrons in the t2g orbitals. A weak Jahn Teller effect is also observed for d5 species.
K4[Cr(CN)6] contains Cr^2+ which is a d4 specie, hence it exhibits Jahn Teller effect. Also, K4[Mn(CN)6] contains Mn^2+ which is a d5 specie, therefore it also exhibits Jahn Teller effect.
