Question

The colour of $KMnO{{}_4}^{-}$ ion is due to :

• A. d-d transition
• B. Intravalence charge transfer
• C. ligand to metal charge transfer
• D. metal to ligand charge transfer

Answer 1

The correct option is C ligand to metal charge transfer

The purple colour of $KMnO{}_4$ ion is due to ligand to metal charge transfer.
In $KMn{O}_4$, the central manganese atom has $+7$ oxidation state. As we know, Manganese has the atomic number of 25 and since the charge is $+7$, the number of total electrons will be 18. The electronic configuration can be written as $\left[Ar\right]3d^{0}4s^0.$ Here, also there are no unpaired electrons and hence d-d transition can't occur.
The oxygen in $KMn{O}_4$ will donate electrons to the vacant orbitals of manganese and as a result a charge transfer spectra occurs and therefore we can say that the colour of $KMn{O}_4$ also arises from charge transfer spectra.