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

Explanation

Mn(II) ion has `3d^(5)` configuration. In the presence of `H_(2)O` molecules acting as weak ligands, the distribution of these five electrons is `t_(2g)^(3)e^(2)g` 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)^(e)` 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.