[kelvinLTR]

Why is the Carbonate ion colourless while the permanganate ion is? It was told the permanganate ion gets the colour by the electron movement within the Oxygen atoms due to the hybrid. Cannot that happen in Carbonate ions as well? I was thinking using MOT there are no unpaired electrons in the Carbonate ion and that might be the reason. Then I tried to draw the MOT of permanganate ion and failed miserably. Any help please?

And I have my inorganic exam tomorrow so quick help appreciated very much

[magician4]

manganese is a B-group element, and you can consider permanganate as to be a B-group element complex.
many of those B-group element complexes are coloured in VIS , due to , for example,  e_g-t_2g electron transition effects: the energy required ( i.e. 10 Dq) often is in the range of VIS light-energy

from another point of view you could call it the HOMO-LUMO energy difference that is suitable for those effects with complexes of B-group elements

... and exactly this (mostly) is NOT true for maingroup "complexes" (if you regarded carbonate to be the oxygene-complex of carbon): the 10 Dq there (there is one, too, yes) , i.e. the HOMO-LUMO difference is much too large to be reached by VIS

... and hence carbonate appears to be colourless


regards

Ingo

[Corribus]

Permanganate is colored because of an LMCT (ligand to metal charge transfer) which transfers electron density from a ligand to an empty metal d orbital.

http://www.webexhibits.org/causesofcolor/8.html