Supramolecular Main-Group Chemistry

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Synthetic chemists have achieved exquisite control of the structure of matter at atomic scale. Their ability to selectively form and rearrange bonds between atoms is behind spectacular advances in the development of new medicinal drugs and materials for advanced technologies, to name a couple of examples. However, manipulating strong interatomic bonds often leads to unwanted side processes; chemical reactions seldom are 100% efficient. Even when by-products are obtained in small amounts and are easily removed, the limited efficiencies of such methods are greatly amplified when a synthesis must be carried out in multiple steps in order to form a large and complex structure. In many instances nature gets around such a problem by using weak bonds, which are easy to break and reconnect; this property allows thermodynamics to spontaneously “correct errors” in the structure. The adaptation of this concept to the control of molecular organization and structure is the basis of supramolecular chemistry. Most work in this area has relied on intermolecular links like hydrogen bridges and the binding of metal ions to electron-rich molecules. In recent years, the affinity of atoms of elements like iodine for atoms bearing lone pairs of electrons has received much attention and the term “halogen bond” has formally been adopted by the International Union of Pure and Applied Chemistry to describe it. Other heavy elements, also from the p-block of the periodic table, have analogous abilities to form supramolecular links. With NSERC support, the Vargas group at McMaster University has pioneered in Canada the systematic study of the application of the supramolecular interactions formed by atoms of sulfur, selenium and tellurium (collectively called “the chalcogens”) to construct functional supramolecular structures. For example, the structure of infinite supramolecular chains of tellurium-containing molecules have been manipulated to engineer crystals with especial optical properties. Another recent achievement is the first demonstration of the ability of tellurium-oxygen “chalcogen bonds” to induce of the spontaneous assembly of discrete, well-defined, aggregates of a few molecules that together possess properties and perform the functions of new molecular entities. Research during the new grant period will build on these successes, expanding the repertoire of supramolecular building blocks and self-assembled structures. These investigations pursue a fundamental understanding of such assemblies but knowledge derived from this is work is highly relevant to applications in areas as diverse as chemical synthesis, optical technologies, electronics and inorganic polymers. As this research program combines a wide variety of experimental and computational methods of modern chemistry, it constitutes an excellent vehicle to train highly qualified personnel for Canadian industry and academia.