28.3.4—Ligand effects on orbital splitting

Different ligands create different electric fields around the same metal ion. That changes ΔE; because ΔE = hf, it changes the frequency and wavelength of light absorbed, so the complementary colour observed can change.

Compare complexes only after holding the metal oxidation state and geometry in view. A stronger ligand-field effect gives a larger splitting and absorption at higher frequency (shorter wavelength).

Replacing water ligands around a metal with ammonia can alter the splitting and shift the absorption band. The solution may therefore change colour even though the central metal and its oxidation state are unchanged.

Do not say a ligand “has a colour that it transfers” to the complex. The observed colour comes from the new energy gap and selective absorption.