Lanthanide supramolecular complexes

There is vast amount of literature involving studies of rare earth complexes with specific guests under the umbrella of supramolecular chemistry. The ligands involved in this area of rare earth complexes are not usually available commercially. In fact the ligands are designed and synthesized and later the rare earth complexes of the synthesized ligands are prepared. An example is cited here to illustrate the scheme involved in the preparation of lanthanide supramolecular complexes. 

This review focuses on the use and limitations of the model-free methods in axial paramagnetic supramolecular mono- and polymetallic lanthanide-containing complexes. A comprehensive survey of the systems with three- and fourfold symmetry for which these techniques have been applied is proposed together with a detailed discussion of the limitations of Bleaney s approach for the modeling of paramagnetic anisotropies and the detection of structural changes along the lanthanide series. 

The ligand p-t-butylcalix[4]arene fitted with phosphinoyl arms is synthesized by refluxing the tetrasodium derivative of p-t-butylcalix[4]arene and chloro(dimethylphosphinoyl) methane in toluene or xylene [88]. The resulting ligand L is reacted with lanthanum perchlorate in acetonitrile to obtain 1 1 and 1 2 complexes, LaL and LaL2- The majority of the supramolecular complexes of rare earths involves the use of organic solvents like toluene, hexane or acetonitrile for the synthesis of both the ligands and lanthanide complexes. 

Metal ions with higher (>6) coordination numbers, such as lanthanides and actinides, have less predictable coordination geometries than lower-coordination-number transition metal and main group ions, while it is difficult to incorporate these ions into rationally designed self-assembled supermolecules, a number of structures have been reported. The unique electronic properties of the /-elements have been exploited in supramolecular complexes to generate functional molecular devices. ... 

Pietraszkiewicz, M., Karpiuk, J., and Rout, A.K. (1993) Lanthanide complexes of macrocyclic and macro-bicyclic N-oxides light-converting supramolecular devices. Pure Appl. Chem, 65(3), 563-566. 

Sabbatini, N. Guardigli, M. Lehn, J.-M. Luminescent lanthanide complexes as photochemical supramolecular devices. Coord. Chem. Rev. 1993,123, 201-228. Sabbatini, N. Guardigli, M. Manet, I. Lanthanide complexes of encapsulating ligands as luminescent devices. Adv. Photochem. 1997, 23, 213—278. 

This last section deals with a few examples of the formation of self-assembly structures from lanthanide complexes, which are formed by using transition metal ions. This area of research is very novel and relatively few examples have been developed to date. While the lanthanide ions have been used to mediate the formation of supramolecular structures, such as helicates, many of which can have both/-/ mdf-d metal ions, etc. the focus here will be on the use of lanthanide complexes and ligand structures similar to those described above [170-173]. 

Supramolecular chemistry is now at the forefront of clinical practice. By linking lanthanide metal-macrocyclic complexes to tissue selective receptors the use of magnetic resonance imaging has become far more useful and widespread. This technique, which relies on the receptor-spacer-reporter motif, has become one of the most powerful medical diagnostics tools available in hospitals worldwide. 

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