In the angular overlap model, the  parameter is related to the strength of the metal-ligand interaction and its variation follows approximately the order of the spectrochemical series. Assuming that (CN-) >> (H2O) explain in terms of the angular overlap model why the Ni2+ ion forms an octahedral complex with H2O, [Ni(H2O)6]2+, and a square planar complex with the ligand CN-, [Ni(CN)4]2-.