Using small atoms and molecules like Lego bricks or Meccano sets, Texas A&M University chemists are trying to design solids -- supramolecule -- that could prove useful in the field of material science, chemical catalysis and molecular separation.

"We are interested in creating new materials with unusual porosity, conducting properties, or catalytic properties," said François P. Gabbaï, a chemistry professor at Texas A&M.

Discoveries in these areas are likely to attract the attention of both the high-tech and chemical industries, Gabbaï added.

The basic "Meccano sets" used in Gabbaï's research are Lewis acids - chemical substances that are electron-deficient and can accept a pair of electrons. These Lewis acids molecules have metal centers embedded in organic backbones of well-defined size and architecture.

"These molecules are electron-deficient," Gabbaï said, "so they want to interact with elements or molecules rich in electrons."

The interaction between electron-poor and electron-rich molecules is used to connect the different pieces together. The material that results is a supramolecule.

In Gabbaï's group, such supramolecules are prepared by self-assembly methods. This means that upon mixing, the Lewis acid and the electron rich compound automatically crystallize together to form fully organized and extended structures.

"We do not have to go step by step like putting one atom at a time. It is a very straightforward and elegant way to synthesize materials," Gabbaï said.

"We are trying to use self-assembly methods to specifically design the shape and the functionality that we want to include in the supramolecules," Gabbaï said. He explained that one must pay attention to the angles in building blocks and to be able to predict the directionality of the bonds.

Gabbaï and his collaborators have built supramolecular materials containing polyfunctional Lewis acids. They discovered that some of these materials could recognize toxic aromatic substances such as benzene. So, the compounds have potential application in pollutant sensing.

Other projects presently under way in Gabbaï's group concern using self-assembly methods to prepare solids with small internal cavities. Gabbaï would then use these solids as filters for molecular-scale separation.

"We would like to prepare a material with cavities fitting the size of methane and not those of larger natural gas molecules," Gabbaï said. He then explained that such solids could be used to separate methane from larger natural gas molecules that usually occur as mixture.

Apart from his interest for self-assembled functional materials, Gabbaï also pursues a number of fundamental projects. In one such project, his group focused on the formation of one-electron bonds. Usually, a bond has two electrons. For example, in a dihydrogen molecule, the two hydrogen atoms share two electrons to form a covalent bond.

Recently, Gabbaï has been able to prepare molecules in which atoms are linked by one-electron bonds. "We have a knack for molecules with unusual bonding situation," he said.

More specifically, they used a bifunctional Lewis acid containing two boron atoms separated by a short distance, and were able to induce the formation of a one-electron bond by putting one electron in between the two boron atoms.

"This is the most exciting discovery that we have made in the last 12 months," Gabbaï said. "Due to the unusual nature of such bonds, this discovery is fundamental but could have applications in the design of new magnetic materials and conductors."

Contact: François P. Gabbaï, 979-862-2070, gabbai@mail.chem.tamu.edu
Ping Wang, 979-862-2694, pw@univrel.tamu.edu.

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