Q. Define the Spectrochemical series?

Spectrochemical series helps us in renationalising the differences in the spectral properties of complexes. As the strength of the crystal field created by the ligands & increases, the frequency of absorption of light by the complex would also increase. Absorption of high frequency radiations means that light of lower frequency will be transmitted and will be responsible for the particular dour of the complex. It thus explains as to why the colours of a series of complexes of one particular metal ion, in the same oxidation state having the - same geometry, could be different. For example, the following four octahedral compounds of Co³ ion show different colours which are in accordance with spectrochemical series. 

Complex                                    D₀ (em-1)                            colours

[Co (C₂O₄)₃]^3-                      18,000                           Dark green

[Co (H₂O)₆]³⁺                       18.200                                Blue

[Co (NH₃)₆]^{3 +}                            22.900                          Golden-brown

[Co (CN)₆]^{3 -}                               33.500                              Yellow