Lanthanide complexes macrobicycles

Schiff base approaches have beenusedto synthesize mono-, di-, andtri-nuclear lanthanide complexes (73-78). Complexes of the macrobicyclic... 

Mono- and bimetallic lanthanide complexes of the tren-based macrobicyclic Schiff base ligand [L58]3- have been synthesized and structurally characterized (Fig. 15), and their photophysical properties studied (90,91). The bimetallic cryptates only form with the lanthanides from gadolinium to lutetium due to the lanthanide contraction. The triplet energy of the ligand (ca. 16,500 cm-1) is too low to populate the terbium excited state. The aqueous lifetime of the emission from the europium complex is less than 0.5 ms, due in part to the coordination of a solvent molecule in solution. A recent development is the study of d-f heterobimetallic complexes of this ligand (92) the Zn-Ln complexes show improved photophysical properties over the homobinuclear and mononuclear complexes, although only data in acetonitrile have been reported to date. 

Mono- and bimetallic lanthanide complexes of the tren-based macrobicyclic Schiff base ligand have been synthesized and... 

Cryptate complexes with macrobicyclic ligands containing three bipy units, in which the Ln + ion is contained within a ligand cavity, have been synthesized. Such ligands will complex Ln + ions, such as Eu + and Sm +, under conditions where Ln + ions are not. An application has been using lanthanide cryptates of the early lanthanides (La, Ce, Eu) as catalysts in the hydrolysis of phosphate monoesters, diesters, and triesters. Schiff base complexes can be synthesized by the reaction of a lanthanide salt with a diamine and a suitable carbonyl derivative such as 2,6-diacetylpyridine. 

The synthesis of ligands bearing mixed type of chelating groiq)s such as amide-bipyridine or amide-phenantroline (e.g. 8) or having a macrobicyclic structures such as 9, allows a good compromise between stability and liuninescence properties of the corresponding complexes with lanthanide ions. 

Macrocyclic ligands and their open-chain analogues have added a new dimension to the coordination chemistry of lanthanide ions. In particular, they allowed the study of high and unusual coordination numbers, e.g. 11-coordination. Basic thermodynamic data are still needed to get a better understanding of the complexation process and of both macrocyclic and macrobicyclic effects. Moreover, kinetic data on ligand exchange remain scarce and studies in this field are certainly desirable. 

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