Which complex exhibits the highest magnetic moment?

To determine which complex exhibits the highest magnetic moment, it’s essential to consider the electronic configurations of the metal ions and the influence of the ligand on their state. In this case, all complexes are coordinated with the same ligand, ammonia, which is a strong field ligand that can lead to varying degrees of crystal field splitting.

In the case of [Co(NH₃)₆]³⁺, cobalt in the +3 oxidation state has an electronic configuration of 3d⁶. Given that ammonia is a strong field ligand, it causes pairing of the electrons in the lower energy orbitals. Therefore, in this complex, there are four paired electrons, leaving two unpaired electrons, which contributes to a significant magnetic moment.

The complex [Fe(NH₃)₆]²⁺ involves iron in the +2 oxidation state with an electronic configuration of 3d⁶ as well. With ammonia as the ligand, this complex typically has four unpaired electrons when considering a high-spin state, creating a magnetic moment but not as high as that of cobalt in the +3 state.

For [Ni(NH₃)₆]²⁺, nickel in the +2 state has an electronic configuration of