Supramolecular chemistry, commonly defined as chemistry 'beyond the molecule,' has seen great advances in both the controlled formation and prediction of multi-molecular assemblies through electrostatic stabilization. Key to supramolecular design is the division of function between the covalent framework of a molecule and the noncovalent interactions included within the molecular frame by choice of chemical functionality. The covalent framework serves as the scaffolding onto which various molecular fragments are added, thereby directing the alignment and defining the shapes of the supermolecules by limiting how these interacting fragments can arrange themselves. The inclusion of noncovalent stabilization into these larger assemblies is by way of any of a number of familiar chemical functionalities. From among such well-studied electrostatic interactions as hydrogen-bonding, metal-ligand coordination, pi-stacking interactions, and dative bonding, intermolecular interactions can be designed and predicted with increasing accuracy. This division between covalency and noncovalency is crucial to supramolecular design, where the strength and predictability of the covalent framework can be relied upon in the assembly of molecules through weaker interactions. Error tolerance, self-correction, and controllable disassembly-reconstitution are all benefits of relying on weaker yet directed interactions between the more stable covalent frameworks.
The formation of structures through supramolecular design has favored the use of very small, repeating molecular subunits to assemble larger structures. The philosophy of supramolecular design need not be limited to the inclusion of noncovalent interactions only onto small molecules. The division of structure and function into covalent frameworks and electrostatic fragments for the design of supermolecules is just as valid over a broader range at the nanoscale, provided the electrostatic interactions between subunits provide stability enough to keep these subunits together under operational conditions.
The applicability and utility of the supramolecular approach to the formation of nanoscale assemblies will be presented using carbon nanotubes as the covalent framework and dative bonding. Carbon nanotubes, having been featured prominently in all aspects of nanoscale endeavors, constitute regular, chemically controllable structures for which the issues of alignment and assembly are still being addressed. Dative bonds are a well-known type of electrostatic interaction between donor/acceptor molecular pairs, and have also been of interest for nanoscale designs where covalency is disfavored for the particular application. Stability and chemistry are considered both for the functionalization of these structures and the actual formation of useful structures. The benefits of dipolar design are discussed relative to current issues in nanotube production, including diameter discrimination and the extended assembly of larger structures. The same design and assembly methods used for these larger structures can be both used for making complex designs and simplified for designing proof-of-principle assemblies from smaller structures more readily handled by solution-phase chemistry.