Supramolecular directing concept

This supramolecular directing concept has led to a family of materials whose structure, composition, and pore size can be tailored during synthesis by variation of the reactant stoichiometry, nature of the surfactant molecule, or by postsynthesis functionalization techniques [113]. 

In many cases, the interactions are directed in accordance with the VSEPR rules, confirming the concept of (donor) —> a (acceptor) overlap. The above collection of structural data reveals that in most cases particular supramolecular networks were observed , not designed . 

Comparable extension has been given to the research on molecular recognition, catalysis and transport processes (Chapters 2-6) on molecular and supramolecular devices (Chapter 8) and self-processes (Chapter 9). This was done to emphasize the more recently developed topics, despite the much larger volume of work on the former areas that have been described in many instances in the literature. The outline of Chapters 1-7 follows that of earlier reviews. Chapters 8 and 9 bring together approaches from various directions. Chapter 10 places the basic concepts into a broader perspective and is intended to make the score decidedly open ended. 

Affinity and selectivity in directional supramolecular systems are composite responses of frequently counteracting influences. The analysis of structure in many instances may then be a dull tool in their study because of the averaging between rapidly interconverting species. Here, an example from abiotic host-guest complexation demonstrates the utility of an energetic analysis how to avoid the pitfall of false reasoning that may follow from all too simple complementarity concepts. 

This dynamic process is commonly known as constitutional dynamic chemistry (CDC). While the concept of dynamic covalent chemistry defines systems in which the molecular (or supramolecular) reorganization proceeds via reversible covalent bond formation/breakage, dynamic systems based on noncovalent linkage exchanges define the concept of dynamic noncovalent chemistry. Dynamic combinatorial chemistry (DCC) can be defined as a direct application of CDC where libraries of complementary functional groups and/or complementary interactional groups interexchange via chemical (i.e., covalent) reactions or physical (i.e., noncovalent) interactions. 

FIGURE 10 Schematic representation of the concepts of covalent and supramolecular catalyst-directing group (42,43). 

Another new concept formulated in conjunction with the formation of the M41S structures was supramolecular templating, i.e. one involving assemblies of molecules (surfactant aggregates, micelles, liquid crystals) [31]. In contrast, microporous materials are templated by isolated molecules acting as structure directing agents. 

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