Question

The purple colour of $\ce{KMnO4}$ is due to the transition

• A. $C.T. (L \to M)$
• B. $C.T. (M \to L)$
• C. $d-d$
• D. $p-d$

Answer 1

Answer: (A)

The permanganate ion has an intense purple colour. Mn (+ VII) has a $d^0$ configuration. So the colour arises from charge transfer and not from d—d spectra.
In $\ce{MnO4^{-}}$ an electron is momentarily changing $\ce{O^{- -}}$ to $\ce{O^{-}}$ and reducing the oxidation state of the metal from Mn(VII) to Mn (VI). Charge transfer requires that the energy levels on the two different atoms are fairly close.
$O = (8) = 2_K , 6_L$
$Mn (25) = 2_K , 8_L , 15_M$
hence the charge transfer occurs from $L \to M $