Features of the complexation of trivalent rare earths

Reasons why chelates of rare earths (RE) do not obey the tetrad 'doublet' effect are discussed. The examination is based on the concept of an ionic metal–ligand bond in RE complexes. The mutual influence of ligands in lower, higher, polynuclear and mixed complexes formed by ligands of low, medium and high denticity is discussed from this viewpoint. Intermolecular interactions in complexes of various structure are examined relative to variations in the volatility of chelates and their selectivity in sublimation and deposition. Structural rearrangement occurring at different points in the RE series for different ligands is proven to be the reason behind the irregular change of properties of RE complexes as a function of RE ionic radius. The bibliography includes 42 references.