Octahedral complexes of copper \( (\mathrm{II}) \) undergo structural distortion (Jahn-Teller). Which one of the given copper \( (\mathrm{II}) \) complexes will show the maximum structural distortion? (en – ethylenediamine; \( \mathrm{H_2N - CH_2 - CH_2 - NH_2} \) )