Chapter 12: Metal Complexes of Rare Earth Elements

Group 3 elements are classified as the rare earths, including the lanthanides and the actinides. Lanthanides and actinides have 4f and 5f valence electrons, respectively, and their properties are significantly different from those of the d-block transition metals. This chapter focuses mainly on the lanthanides and discusses the properties of the 4f elements. The radii of the electronic distributions of the 4f orbitals are small and they behave like inner-shell electrons. Therefore, the 4f orbitals are not involved in bond formation and hence the orbital angular momentum is retained. The unique magnetic properties of lanthanide complexes are attributed to the presence of orbital angular momentum. The electronic structure is described by LS coupling (Russell–Saunders coupling), which is largely unaffected by the ligands. For this reason, the photochemical properties of luminescent lanthanide complexes are extremely unique; the spectrum is extremely sharp, the emission lifetime is long, and the emission colour is always constant, regardless of the ligands or the structure of the complex. Since the 5f orbitals have a wider spatial distribution and are partially involved in bond formation, their chemical properties are intermediate between those of the d-block elements and the lanthanides.