Ligands supramolecular chemistry

Lanthanide Complexes with Multidentate Ligands Supramolecular Chemistry from Sensors and Imaging Agents to Functional Mononuclear and Polynuclear Self-Assembly Lanthanide Complexes. 

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. 

The demonstration of the formation of a hexanuclear zinc complex with the S-donor ligand 2-aminoethanethiolate, containing Zn3S3 and Zn4S4 cyclic units, contributes to the building up of a pattern of polynuclear complex formation based on coordination preferences of the metal ions involved (320) - reaction of Zn2+ with salicylideneamino ligands and pyrazine can give linear tetranuclear complexes (321). Another hexanuclear zinc complex appears in the section on supramolecular chemistry below (Section VII.D). 

This range is for tripodal ligands - a log value of about 59 has been estimated for the Fe + complex of an encapsulating tris-catecholate ligand (Vogtle, F. Supramolecular Chemistry -, Wiley Chichester, 1991, Section 2.3.7.)-... 

In the present volume, our intention was to cover several modern approaches to phosphorus chemistry which were not, or at least not completely, covered in the previous volumes. The selected topics are expected to have broader relevance and to be interesting to a more general readership, since key aspects of phosphorus chemistry are pointed out. Indeed, several fields are investigated coordination chemistry, catalysis, supramolecular chemistry, biochemistry, hybrid organic-inorganic materials, new ambiphilic ligands, and biology. 

It should be noted that the word complex , often used in supramolecular chemistry, is not very specific. It is applied to charge-transfer complexes like the one formed by 21 with 22 [30] as well as to coordination complexes consisting of one or more atoms or ions with n ligands like K2[Pt(N02)4]. The same name complex also covers the Whitesides hydrogen bonded systems [10] shown in Figure 1.1 and inclusion complexes of 4 embedded in 5. Thus the term complex without any adjective has no specificity and can be applied to any type of molecular associates. 

Supramolecular chemistry also provides new tools for catalyst anchoring. We have shown that catalysts can be noncovalently attached to various soluble and insoluble supports, affording recyclable catalysts. Interestingly, the reversible nature of the noncovalent bond gives rise to new opportunities. In the first instance, we foresee an important role for supramolecular bidentate ligands in combinatorial catalysis - but as a consequence of the entirely new properties many new applications are envisioned. We look forward to new developments and results in this exciting emerging area of supramolecular catalysis. 

While today the construction of such bidentate phosphine ligands with the use of an assembly metal is referred to as supramolecular chemistry, this is not to say that there are no examples in older literature utilizing this principle. Actually, there are many and using as a search term hetero bimetallic complexes (a named coined in the early 1980s) leads us to a plethora of complexes. For instance in complex 29, reported by Rauchfuss in 1982, one would consider copper as the assembly metal and platinum as the potential catalytic metal [70]. 

Despite the examples already knovm of ligands having wide bite angles, their synthesis vfith covalent bonds remains tedious and supramolecular chemistry is a powerful tool for the expedient generation of libraries of ligands (Chapters 8 and 9) with different bite angles and other properties. 

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