Coordination Chemistry of the Lanthanides

Forty years ago, very little was known about lanthanide complexes. By analogy with the d-block metals, it was often assumed that lanthanides were generally six coordinate in then-complexes. We now know that this is not the case, that lanthanides (and actinides) show a wider variety of coordination number than do the d-block metals, and also understand the reasons for their preferred choice of ligand. 

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General aspects of the coordination chemistry of the lanthanides with reference to the complexes of neutral oxygen donor ligands are dealt with in this section. For con venience, this section is subdivided into three parts 1. synthetic procedures, 2. stoichiometry, and 3. coordination numbers and coordination polyhedra. 

Coordination Chemistry of the Lanthanide Elements — One Hundred Years of Development and Understanding... 

Subsequent developments prior to the 1940 were meager, and even as late as 1953 the significant aspects of this area were reviewed in terms of only 60 literature citations (55). Yet a 1965 review covering published information only through 1962 required in excess of 500 references (55), and the current literature contains literally a fiood of accounts of various aspects of the coordination chemistry of the lanthanide elements. 

Since the present chapter focuses on the similarities and differences in the coordination chemistry of the lanthanides and actinides, major attention is given to the solution chemistry of the common oxidation states (+ 2, +3 and +4) and consideration of the higher oxidation states is included only when relevant to the general discussion. 

Apart from simple hydrated salts, httle was known about the coordination chemistry of the lanthanides until the 1960s. It was generally assumed that complexes of the Ln + ions resembled those of the transition metals, though there was httle hard evidence to support that view, in particular, the assumption that six-coordination would be the norm. It was known that ligand-field effects were weak in lanthanide chemistry, and so that, combined with the knowledge that lanthanide ions were substantially bigger than typical transition metals, it could have been predicted that coordination numbers greater than 6 would be the norm. Verification of this, however, had to wait for the renaissance... 

It is clear that a detailed understanding of the interactions between the lanthanide ions and amino acids is critical to the evaluation of how these unique metal ions may impact biological systems and human life. The study of the coordination chemistry of the lanthanides thus becomes not only necessary but also significant. 

Moeller, T., 1967, Coordination Chemistry of the Lanthanide Elements-One Hundred Years of Development and Understanding, in G. Kauffman, ed., Werner Centennial (American Chemical Society, Washington,... 

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