Lanthanides coordination capabilities

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. 

With almost all of the conceivable coordination chemistry of the expanded porphyrins still left to be explored, it cannot be over-stres that the potential for new chemistry is enormous. This is i rticularly true when account is made of the fact that the chemistry of the metalloporphyrins has played a dominant role in modern inorganic chemistry. What with the possibility to enhance the stability of imusual coordination geometries (and, perhaps oxidations states) and the ability to form stable coordination complexes with a variety of unusual cations including those of the lanthanide and actinide series, the potential for new inorganic and organometallic discoveries are almost unlimited. For instance, as with the porphyrins, one may envision linear arrays of stacked expanded porphyrin macrocycles which may have unique conducting properties and/or which could display beneficial super- or semiconducting capabilities. Here, of course, the ability to coordinate not only to cations but also to anions could prove to be of tremendous utility. 

Another bidentate ligand whose complexes have been studied in some detail is 1,8-naphthyridine (naph) which, like nitrate, has a small bite angle and is similarly capable of affording high coordination numbers two types of perchlorate complexes have been made, M(naph)6(C104)3 (M = La-Pr) and M(naph)5 (0104)3 (M = Nd-Eu). The former complexes have 12-coordinate lanthanides, confirmed by diffraction methods for the praesodymium complex. The change in stoichiometry is doubtless a manifestation of the lanthanide contraction. 

Fig. 7. Formula of a dendrimer containing 18 amide groups in its branches and 24 chromophoric dansyl units in the periphery, capable of coordinating metal ions (Co ", Ni, or lanthanide ions), and the corresponding scheme (Fig. 2d).

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