The hexaquo manganese (II) ion contains five unpaired electrons, while the hexacyano ion contains only one unpaired electron. Explain using crystal field theory.

Explanation

Mn(ll) ion has `3d^(5)` configuration. In the presence of `H_(2)O` molecules (acting as weak peld ligands), the distribution of these five electrons is `t_(2g)^(3)e_(g)^(2)` i.e., all the electrons remain unpaired to form a high spin complex.

However, in the presence of `CN^(-)` (acting as strong field ligands), the distribution of these electrons is `t_(2g)^(5)e_(g)^(0)` i.e., two `t_(2g)` orbitals contain paired electrons while the third `t_(2g)` orbital contains one unpaired electron. The complex formed is a low spin complex.