Ligands are molecules that bind to metal ions or clusters to form metal complexes. In functional metal complexes, ligands play a vital role in determining the properties and applications of the complexes. They affect the stability, reactivity, and optical properties of the metal complexes. Functional metal complexes with specific ligands are used in various applications such as catalysis, luminescence, and magnetism. For example, catalysts with specific ligands can catalyze chemical reactions with high selectivity and activity. Luminescent metal complexes can be used in lighting, display, and sensing applications.