Q. 49 What is the relationship between observed colour of the complex and

the wavelength of light absorbed by the complex?

When white light falls on the complex, some part of itis absorbed. Higher the crystal field

splitting energy, lower will be the wavelength absorbed by the complex. The observed

colour of complex is the colour generated from the wavelength left over

e.g., if green light is absorbed, the complex appears red.

in terms of crystal field theory, suppose there is an octahedral complex with emply eg level 

and unpaired electrons in thet, level in ground level, I the unpaired electron absorbs light

corresponding is blue-green region, it will excite toe, level and the complex will appear

violet in colour.

in absence of ligand, crystal field splitting does not occur and the substance is colourless.

e.g., anhydrous CuSO4 is while, but CuSO45H2O is blue in colour.