Octahedral metal complexes supramolecular

Bipyridines were efficiently used in supramolecular chemistry [104], Since the molecule is symmetric no directed coupling procedure is possible. In addition, 2,2 6/,2//-terpyridine ligands can lead to several metal complexes, usually bis-complexes having octahedral coordination geometries [105,106], Lifetimes of the metal-polymeric ligand depend to a great extent on the metal ion used. Highly labile complexes as well as inert metal complexes have been reported. The latter case is very important since the complexes can be treated as conventional polymers, while the supramolecular interaction remains present as a dormant switch. 

Sasaki and coworkers have examined reversible metal coordination as a mechanism for DCL generation in the presence of lectin biomolecules [49,50]. The use of metal ions in reversible processes is canonical to supramolecular chemistry, and has been explicitly demonstrated for doublelevel orthogonal DCLs by Lehn and Eliseev [51]. Sasaki s system is designed around octahedral Fe(II) bipyridine complexes. The bipyridine-modified A-acetylgalactosamine (bipy-GalNAc) (78) was found to trimer-ize in the presence of Fe(II) to afford a 3 1 mixture of the fac (79) and mer (80) diastereoisomers, each as a racemic mixture (A+A) (Scheme 2.12). 

Further parameterization may be necessary when modeling square planar and octahedral geometries around transition metals. Historically, problems arose when ideal angles of 90° were involved as minimization algorithms using an iterative approach allowed two ligating atoms separated by less than 90° to collapse into each other. The consequences for inorganic and supramolecular coordination chemistry were profound however, force fields are now able to reproduce coordination complexes accurately. 

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