Colours In Complexes:-

Change in colour in complexes is due to

1. Unpaired e^-
2. Charge transfer
3. Polarization

1. d – d transition or f – f transition since d – orbitals exist in more than one different energy level. There unpaired e^‑ electron can make transition between t2g and eg. But it should be that always complementary colour is observed.

If legand is strong high energy radiation is absorbed to make transition and low energy radiation is reflected therefore colour is appeared towards yellow red side.

If legand is weak low energy is absorbed and high energy is reflected. Colour is appeared towards blue-green side .

It means the colour spectrum is just opposite to hydrogen spectrum.

2. Unpaired e^-:-  

Some time complex does not contain any unpaired electron but  different colour appeared in  complex with different metal. it is due to charge transfer between internal and external metal.