Colour of complexes

What determines intensity of colour of a complex

How well it obeys the selection rules

What are the selection rules

Spin selection rule - trnasitions between states fo different spin are forbidden

Laporte (Parity) selection rule - transitions must occur between states of different parity i.e. u to g. This also leads to the selection rule requiring a change in orbital angular momentum. However this only applies to centrosymmetric metal complexes.

What allows d-d transitions to occur

Vibronic coupling distorts the complex, removing symmetry and leading to p-d mixing and allowing d-d transitions

what is charge transfer

Relative intensities of absorption from transitions