Tridentate binding units as structural patterns for the design of nine-coordinate lanthanide building blocks with predetermined properties

The use of rigid receptors displaying preorganized cavities for the selecti ve complexation of spherical ions has shown some limitations for trivalent lanthanide metal ions, Ln(III), because of the minor variation of their ion ic radii. The recent development of semi-rigid ligands derived from macrocy clic platforms grafted with complexing pendant arms or from tripodal podand s leads to an unprecedented fine tuning of the structural, thermodynamic an d electronic properties of the lanthanide complexes, thus opening new persp ectives for the design of functional molecular or supramolecular devices. T he application of the Induced fit concept for the design of covalent and no n-covalent nine-coordinate monometallic and polymetallic podates is emphasi zed together with applications as light-converters, thermal and electrochem ical switches and template agents. The step-by-step evolution from rigidity to flexibility in lanthanide coordination chemistry is presented and the b asic recognition processes responsible for the tuning of the metallic site are discussed. (C) 2000 Elsevier Science S.A. All rights reserved.