Which ligands are most commonly associated with MLCT?

Metal-to-ligand charge transfer (MLCT) is a phenomenon where an electron is transferred from a metal center to a ligand, resulting in an excited state of the complex. Diimines, such as ethylenediamine or various derivatives, are known for their capability to participate in MLCT due to their π* orbitals that are energetically accessible and lie sufficiently low in energy relative to the metal d-orbitals.

When a metal ion is coordinated to diimines, the electronic structure allows for effective overlap between the metal d-orbitals and the π* orbitals of the diimine ligands. This overlap facilitates electron transfer during excitation, leading to characteristic absorption bands in the UV-Vis spectrum associated with MLCT.

In contrast, halides, alkyl groups, and phosphines have different electronic characteristics that do not support metal-to-ligand charge transfer to the same extent. Halides are often associated with ligand-to-metal charge transfer (LMCT) in many cases instead. Alkyl groups are generally poor π-acceptors and favor σ-bonding rather than π-bonding interactions essential for MLCT. Phosphines, while good σ-donors, typically do not stabilize charge