Metal preparation, supramolecular polymer

In our pursuit of metal-coordinating supramolecular polymers, we prepared compound 8 so that it has a bipyridyl (bipy) linker coimecting two PDl moieties. One of the consequences of having bipy is the completely flat geometry of the... 

A relatively new field called supramolecular chemistry has been developed over the last three decades. Supramolecular assemblies and supramolecular polymers differ from macromolecules, where the monomeric units are covalently linked. In a supramolecular polymer, the monomeric units self-assemble via reversible, highly directional, noncova-lent interactions. These types of bonding forces are sometimes called secondary interactions. Hydrogen bonding is the secondary force most utilized in supramolecular chemistry, but metal coordination and aromatic tt-tt electronic interactions have also been used. From a materials standpoint, supramolecular assemblies are promising because of the reversibility stemming from the secondary interactions. The goal is to build materials whose architectural and dynamical properties can respond reversibly to external stimuli. Solid phases are prepared by self-assembly from solution. In the solid-state, supramolecular polymers can be either crystalline or amorphous. 

A combination of two different supramolecular forces, namely metal-metal bonds and the ureidopyrimidones were investigated by Schubert et al. [136,137] (Fig. 35). A poly(g-caprolactame) was prepared—with a ter-pyridine moiety at one end and an ureidopyrimidone unit at the other end—via tin-octanoate catalyzed polymerization. Together with iron(ll) ions, double supramolecular polymers formed from chloroform solution. Again, solid-like behavior was observed, similar to results for the purely hydrogen-bonded polymers. 

This chapter has analyzed the principal methods, structural organization and architecture of a wide range of metallopolymers obtained by incorporation of metal particles into polymers, as well as promising new ones. The multiplicity of architectural structures in such self-organized systems is a reflection of the infinite variety of natural objects coupled with the synthetic possibilities of chemistry. Even the term supramolecular architecture has appeared [104]. Almost all architectural forms (including those obtained by sol-gel methods in thin-layered films) are used in nature for generation of metal particles in biopolymers and their analogues. Primarily, this relates to supramolecular polyfunctional systems such as enzymes, liposomes and cells. The processes of nanocomposite preparation are very similar to biomineralization, biosorption etc. 

Rowan and coworkers took advantage of the ability of lanthanide metals to form complexes with up to three tridentate ligands and prepared multiresponsive metaUo-supramolecular polymer gels from linear ditopic macromonomers... 

Building on this concept, Takacs et al. have reported the construction of a chiral bidentate phosphate ligand by assembly via a heteroleptic complex thus, it was proposed that if a supramolecular polymer could be prepared around a structural metal atom (Ms), then a second metal can be coordinated that acts as the catalytically active site (Meat, Scheme 6). 

The use of metal-ligand coordination in preparing supramolecular assemblies represents one of the major themes of materials chemistry over recent years. Notable achievements have been made in both the assembly of discrete clusters in solution and extended coordination polymers in the solid state,including metal organic frameworks (MOFs). The assembly of coordination polymers on surfaces is far less studied and, it would appear, more synthetically challenging. However, some notable studies have been reported both at the solid-solution interface and under UHV conditions. 

In addition to mesostructured metal oxide molecular sieves prepared through supramolecular assembly pathways, clays, carbon molecular sieves, porous polymers, sol-gel and imprinted materials, as well as self-assembled organic and other zeolite-like materials, have captured the attention of materials researchers around the globe. Clays, zeolites and sol-gel materials are still very popular because of their extensive and expanding applications in catalysis and separation science. Novel carbons and polymers of ordered porous structures have been synthesized. There are almost unlimited opportunities in the synthesis of new organic materials of desired structural and surface properties via self-assembly or imprinting procedures. 

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