Supermolecules, synthesis

ZiesselR Synthesis (1999) 11 1839-1865 Making new supermolecules for the next century multipurpose reagents from ethynyl-grafted oligopyridines... 

The continued interest in dendritic materials as well as the related hyperbranched polymers has sparked the imagination of researchers in many different areas. The incredible increase in annual publications in this topic is best shown in the Figure and thus as the number on new building blocks and core molecules proliferate, the structural composition of precise and controlled design will grow to meet the imagination of molecular architects. This review series was initially conceived to cover the synthesis and supramolecular chemistry of dendritic or cascade supermolecules as well as their less perfect hyperbranched cousins. 

These few examples show that Hekates of all subgroups (i)-(iii) can be formed by supramolecular interactions, too, which make their synthesis even more versatile. The only obvious limitation of the supramolecular approach is that the individual components should not themselves form H-bonded networks or crystallise and thus precipitate from the mixture. This may be the reason that not many Hekate LC supermolecules are known presently. 

Two basic approaches for the synthesis of inorganic supermolecules and one-, two-, and three-dimensional coordination polymers have been developed ... 

The concept of supermolecular chemistry, chemistry of very large molecules, is also of great current interest and is relevant to both crystal engineering and supramolecular chemistry. When one considers the development of supermolecules , the 1990s will probably be regarded as the key time period in which the basic concepts were delineated and experimental results were forthcoming. Indeed, we have witnessed synthesis and characterization of the largest hydrocar-... 

These principles of crystal engineering and supramolecular synthesis have thus far been used to design, isolate, and characterize network structures from relatively small molecular components. In the context of coordination polymer networks, a recent review indicates how wide the range of chemical components and accessible network motifs has become.48b However, the scale of these structures is such that cavities and channels are on the order of 1 nm and, to date, each cavity is identical. Careful selection of appropriate substrates or components and ever more control over crystal packing will offer the potential for rational design of an even more extensive array of modular (i.e. binary, ternary, or even higher order) structures than those that are currently available. In particular, judicious choice of supermolecules... 

Generally speaking, there are two ways by which molecular electronics is to be realized. The first employs a molecular component system consisting of different molecules with different functions. These molecules are expected to act cooperatively and form a device. In this system, the point is how to assemble different molecules in a desired manner and how to endow the molecular assemblies with the specific functions that are aimed at. The alternative method relies on a supramolecular system that takes advantage of the multiple functions of the supermolecules. The functions of this system depend not only on the relative arrangement of the supermolecule in the material but also on the position of each functional unit in the supermolecule, which stresses the importance of the molecular design and its synthesis. The more sophisticated way would be to fabricate the materials consisting of different supermolecules, which is yet to be realized. 

By analogy with the synthons of organic synthesis, Desiraju [16] introduced the term supramolecular synthon to describe the structural units within supermolecules which can be formed and/or assembled by known or conceivable synthetic operations involving intermolecular interactions . Such supramolecular synthons (often abbreviated to synthons in the literature, and hereafter) can involve two identical or different components (Fig. 1). 

This topic was partially covered in CHEC-II(1996) <1996CHEC-II(9)809> under the subentry Catenanes and Rotaxanes . In this section, emphasis is given to the design and construction (and to some extent, the properties) of supramolecular architectures derived from or incorporating crown ethers rather than to the synthesis of the crown ether component present in them. The crown ether rings described herein are either covalently linked (dendrimers), mechanically interlocked (rotaxanes, catenanes), or just bound by noncovalent interactions (pseudorotaxanes) to the rest of the supermolecule to which they belong. 

Volume 4 is dedicated to three important topics Catalysis (Part 4.1), Heterogeneous Systems (Part 4.2), and Gas Phase Systems (Part 4.3). The six chapters of Part 4.1 cover the most important aspects of electron transfer catalysis, from fundamental concepts to organic synthesis, from carbon dioxide fixation to protein catalysis, from redox modulation to biomimetic catalysis. Part 4.2 deals with the basic aspects and the latest developments in electron transfer on semiconductors, dye-sensitized electrodes, mono- and multilayers, intercalated compounds, zeolites, micelles and related systems. Part 4.3 covers gas phase systems, from atoms to small molecules, exciplexes, and supermolecules. 

Despite the inherent difficulties with using weak forces as primary synthetic tools, considerable progress has been made, and the preponderance of strategies for supramolecular synthesis prompted Desiraju [19] to introduce the term supramolecular synthon . Synthons describe the precise recognition events that take place when molecules assemble into supermolecules and provide an important illustration of the conceptual similarities between retrosynthetic organic synthesis and supramolecular assembly [20]. 

Fig. n.i. Reaction scheme of the formation of supermolecules via non-covalent synthesis. 

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