Are Ligand-to-Metal Charge Transfer (LMCT) and Metal-to-Ligand Charge Transfer (MLCT) characterized as localized or delocalized?

• A. Localized
• B. Delocalized
• C. Partially localized
• D. Neither localized nor delocalized

Answer: (B)

The main idea is that LMCT and MLCT transitions involve moving electron density between the ligand and the metal through covalent metal–ligand bonding. Because the frontier orbitals in these complexes are formed by mixing metal d-orbitals with ligand orbitals, the excited-state wavefunction has significant contributions on both the metal and the ligand. That means the charge transfer is not confined to one fragment; the electron density is spread over the metal–ligand framework. In LMCT, an electron is excited from a ligand-based orbital into a metal-based orbital, and in MLCT, an electron is promoted from a metal-based orbital into a ligand-based orbital. In both cases, the resulting excited state is delocalized across the complex rather than strictly localized on either the metal or the ligand, which is why these transitions are described as delocalized.