Coordination Compounds

The complex ion [Mn(Cl)6]3− has a spin-only magnetic moment of 4.90 B.M.
Oxidation State and Electron Configuration:
For Mn in this ion, the oxidation state is +3 . This means manganese has lost three electrons.
The electron configuration for Mn3+ is [Ar]3d4. This tells us the ion has 4 electrons in the 3 d orbitals.
Finding the Magnetic Moment:
The formula for the spin-only magnetic moment is:
µ=√n(n+2)‌ В.М. ‌
Here, n is the number of unpaired electrons. For Mn3+,n=4 because there are 4 unpaired electrons in the 3d orbitals.
Plug in the value of n :
µ=√4(4+2)=√24=4.90‌ В.М. ‌