Question

What is the basis of formation of the spectrochemical series?

Answer 1

Spectrochemical series is a series in which the ligands have been arranged in order of increasing field strength.

\[\ce{I^- < Br^- < SCN^- < Cl^- < S^{2-} < F^- < OH^- < C2O^{2-}_4 < H2O < NCS^- < EDTA^{4-} < NH3 < en < CN^- < Co}\]

CN⁻ is a strong field ligand and H₂O is a weak field ligand hence magnitude of CFSE is different. This leads to a different colour.