ABSTRACT
Trivalent lanthanides are naturally expected to be accommodated with various macrocyclic ligands to form stable complexes similarly to alkaline and alkaline earth metals because of the similarity of the ionic radii between lanthanides and Na+ or Ca2+ ions. Colors of most macrocyclic complexes with lanthanides are the same as those of the parent salts if the ligands are colorless. Vibrational spectra, especially Infrared (IR) spectra, have been measured for many lanthanide-macrocycle complexes. Solvent extraction of lanthanides with crown ethers has been investigated using picrate as a counteranion in most cases because of large distribution ratios. The divalent state of some lanthanide ions is stabilized by complexation with macrocyclic ligands, though divalent lanthanides are usually able to be oxidized to trivalent ones. Some lanthanide complexes with macrocycles are proposed as NMR shift reagents, as stated in the as Nuclear magnetic resonance (NMR) section. Luminescent lanthanide ions are often used as probes to solve analytical and structural problems.
