Why are different colours observed in octahedral and tetrahedral complexes for the same metal and same ligands ?

Explanation

Extent of spilitting of d-orbitals is different in octahedral and tetrahedral field. CFSE in octahedral and tetra federal field are closely related as.
`Delta_(t)=(4/9) Delta_(o)`
Where, `Delta_(t) =` crystal field splitting energy in tetrahedral field
`Delta_(0) =` crystal field splitting energy in octahedral field
Wavelength of light and CFSE are related to each other by fomula
`Delta_(0)=E=(hc)/lambda`
`E prop 1/lambda`
So, higher wavelength of light is absorbed in octahedral complexes than tetrahedral complexes for same metal and ligands. Thus, different colours are observed.