Macrocyclic ligands, lanthanide complexes stability

AC and AEC complexation is also effected efficiently by other macrocyclic ligands such as the spherands 13, cryptospherands 14 [2.9, 2.10], calixarenes [2.38, A.6, A.23], torands [2.39], etc., some of them, for instance the spherands displaying particularly high stabilities. A special case is represented by the endohedral complexes of fullerenes in which the cation (Sr2, Ba2+, lanthanides) is locked inside the closed carbon framework [2.40],... 

The importance of the chelate effect combined with the construction of multidentate ligands is well known in lanthanide chemistry. This is expressed in the rich coordination chemistry of / -diketonates [88] or complexes with Schiff bases [89] and macrocyclic polyethers [90] where lanthanide cations achieve steric saturation by high coordination numbers. Entrapment of the cation in a macrocyclic cavity results in greater complex stability. However, simply functionalized ligands such as ethanolamines can also supply a suitable ligand sphere [91-93],... 

Stability constants of rare earths with a variety of macrocyclic ligands are presented in Tables 3.13 to 3.19 (see Appendix) and the associated references are given at the bottom of the tables. As is the case with noncyclic ligands, stability constants are determined by several different techniques. One should be careful when comparing the values, since different conditions and techniques might have been applied. Stability constants for the complexes of cations with macrocyclic compounds are often influenced by the relative sizes of the cations and the cavities of the macrocycles, and hence the macrocycles have specific selectivities to various cations. It is naturally expected that macrocyclic compounds also exhibit unique selectivities to lanthanides. 

Lanthanide complexes with macrocyclic ligands such as those based on 1,4,7,10-tetraazacy-clododecane or polyaminocarboxylates have been studied extensively by CPL spectroscopy. These complexes often possess large stability constants in aqueous solution and, moreover, present interesting chiroptical properties. There have been a number of reports of CPL... 

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