Trivalent lanthanide ions: versatile coordination centers with unique spectroscopic and magnetic properties

At first sight, trivalent lanthanide ions Ln(III) are not very attractive t o the chemist: the spherical entities with "inner" 4f valence electrons int eract electrostatically with their surroundings, display little stereochemi cal preferences, and have very similar chemical behavior. On the other hand , these ions exhibit rich and unique spectroscopic and magnetic properties that can be taken advantage of either for spectroscopic and magnetic probes , or to construct materials with specific physico-chemical properties. More over, the intrinsic chemical drawbacks of the Ln(III) ions can be turned in to a benefit since the ions adapt easily to almost any chemical environment and can therefore be readily introduced into a variety of ionic, molecular , and supramolecular edifices where they act as functional centers. We will first outline the historical aspects of Ln(III) coordination chemistry. Fu ndamental properties of the Ln(III) ions, including coordination numbers an d geometries, solvation, hydrolysis and thermodynamic aspects of complexati on, are then briefly reviewed. We finally focus on the several methods deve loped by inorganic chemists to trap the elusive lanthanide ions into enviro nments preserving or even enhancing their physical properties, or increasin g the differences in their chemical characteristics. (C) 2000 Elsevier Scie nce S.A. All rights reserved.