Lanthanides coordination chemistry

Aminopyridinato ligands form a special class of anionic ligands in which an aromatic ring is part of an amidinate system. These ligands have frequently been employed in early transition metal and lanthanide coordination chemistry. Their diverse and interesting chemistry has been described in detail by Kempe et al. ° and will thus be covered here only briefly. Typical reaction pathways leading to titanium aminopyridinato complexes are outlined in Scheme 169. Metathetical as well as salt-free routes have been developed. 

In conclusion, the search for improved Gd(III)-based agents has been highly beneficial for the growth of lanthanide coordination chemistry and has created a very fertile interdisciplinary area with contributions from Chemistry Biology Medicine, and Imaging technology. The requisite for... 

Lanthanide coordination chemistry has seen a considerable increase in interest in recent years due to potential applications in a variety of fields, including catalysis (9), biochemical analysis (3-8,10-14), and non-invasive diagnostics (8,15,16). 

The bipyridyl chromophore has been extensively used in lanthanide coordination chemistry. In addition to those based on the Lehn cryptand (see Section IV.B.4), a number of acyclic ligands have also employed this group. One such ligand is L17, which binds to lanthanide ions such that one face of the ligand is left open (Scheme 3) (60). As expected, luminescence is extremely weak in water and methanol, but stronger in acetonitrile ( = 0.30, 0.14 for europium and terbium, respectively). In addition, the nature of the counter ion can... 

Due to the presence of hard anionic oxygen atoms, phenolate and carboxylate groups are often employed as donors in lanthanide coordination chemistry. Ligand [L18]4- is reported as an excellent triplet sensitizer for lanthanide luminescence (61). Indeed aqueous lifetimes of 0.57 and 1.61 ms are reported for europium and terbium, respectively quantum yields of 0.20 and 0.95 respectively refer to the efficiency of the energy transfer process alone. 

The importance of the carboxylate donors is underlined by a study of the lanthanide coordination chemistry of the similar terdentate ligand 2,6 -bis( 1 -pyrazol-3 -yl)pyridine, L24 (63). The complex structure of [Tb(L24)3][PF6]3, shown in Fig. 11, appears to be fairly robust in methanolic solution, with Horrocks analysis (q = 0.6) suggesting the 9-coordinate structure is retained the small quenching effect of outer sphere coordination explains the q-value. However, in aqueous solution, the lability of the ligands dramatically changes the luminescence. Whilst the emission decays are not exactly single exponential, approximate lifetimes in H20 and DoO suggest a solvation value of 4-5. 

One of the most studied class of macrocyclic ligands in lanthanide coordination chemistry is without any doubt the molecules derived from cyclen, a 12-membered ring bearing four amino functions. In particular, its tetracarboxylic derivative H4DOTA (see Fig. 4.40) was synthesized in 1976 by a German chemist, H. Stetter from the University of Aachen,... 

Tetrad Effect of Lanthanide Elements - Changing Gradation Rules in Lanthanide Coordination Chemistry... 

Using carefully chosen literature examples, specific features of the lanthanide coordination chemistry using aliphatic alkoxido, aryloxido, and macrocyclic polyaryloxido ligands are discussed below. For each ligand type, those bearing simple, spectator-like non-coordinating substituents and those functionalized with donor groups capable of metal coordination will be treated separately. 

The foregoing example suggests that with the use of macrocyclic polyaryloxide ligands, different lanthanide coordination chemistry may be anticipated as a result of the constrained... 

The large number of lanthanide alkoxide complexes featuring the inclusion of oxo or hydroxo groups unmistakably suggests that the coordination chemistry of lanthanide hydroxide is intimately associated with that of the alkoxides. Arguably the simplest and most ubiquitous O-containing ligand, the water molecule, occupies a special position in the development of lanthanide coordination chemistry. Upon coordination to the Lewis acidic lanthanide ion, an... 

Tsukube, H., Shinoda, S., and Tamiaki, H. (2002) Recognition and sensing of chiral biological substrates via lanthanide coordination chemistry. Coordination Chemical Reviews, 226, 227. 

Recognition and sensing of chiral biological substrates via lanthanide coordination chemistry using complexes with porphyrins 02CCR(226)227. 

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