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 in +2 state has the configuration `3d^(5)`. In presence of `H_(2)O` as ligand, the distribution of these five electrons is `t_(2g)^(3)` `e_(g)^(2)`, i.e., all the electrons remain unpaired. In presence of `CN^(-)` as ligand, the distribution 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.