Question

$Mn{O}_4^{-}$ is of intense pink colour, though $Mn$ is in (+7) oxidation state. It is due to__________.

• A. oxygen gives colour to it
• B. charge transfer when Mn gives its electron to oxygen
• C. charge transfer when oxygen gives its electron to Mn making it Mn(+VI) hence, coloured
• D. None of the above is correct

Answer 1

Answer: (C)

charge transfer when oxygen gives its electron to Mn making it Mn(+VI) hence, coloured

The color in $MnO{4}^{-}$ arises from an electronic transition, but it is actually not a d-d transition, since the Mn in this compound has no d electrons. It arises from a charge transfer reaction within the molecule, in which photons promote an electron from the highest energy molecular orbital in one of the Mn-O bonds to an empty d orbital on the manganese. This promotion is equivalent to the energy of a yellow photon, so yellow light is absorbed leaving us to see purple, the complementary color.