Rare earth coordination compounds: from monodentate ligands via crown ether complexes to a variety of bidentate ligands

With a wide range of ionic radii, the rare-earth ions, M3+, exhibit a large variety of coordination geometry. Coordination numbers vary from 6 (octahedron) to 12. Ligands may be monodentate like halide ions and water molecules, bidentate like acetate, proprionate, beta-diketonates, tetra- to hexadentate as with crown ethers, hexadentate like tetraglyme. The coordination polyhedra might be monomers, di- or trimers or they may be incorporated into chains, layers, or even networks. Therefore, from a plethora of structures, complexes with special properties (optical, magnetic) might in principle be tailored. (C) 2000 Elsevier Science S.A. All rights reserved.