Polyoxometalates as ligands for functional lanthanoid complexes

Considerable current interest in the chemistry of complexes of lanthanoid (Ln) metals owes much to the unique chemical and physical properties of the trivalent lanthanoid ions. These properties have given rise to a number of important applications, including as magnets (in computer hard drives, speakers and in the motors of cordless tools) and as phosphors (in televisions and fluorescent lights). The trivalent lanthanoid ions have relatively large ionic radii and thus often exhibit high coordination numbers. They are hard Lewis acids and in their coordination complexes tend to bind to ligands with hard Lewis donor atoms, particularly oxygen. Because the 4f orbitals that contain the valence electrons do not extend out far enough from the nucleus to interact significantly with ligand orbitals, the lanthanoid-ligand bonds have significant ionic character.