Chemists Create Molecular Flasks

Chemical reactions happen all of the time: some things burn or rust, others react to light exposure--even batteries use chemical reactions to supply electricity. One of the big challenges chemists continually face is finding new ways to control these reactions or create conditions that promote desirable reactions and limit undesirable ones. Recently, researchers at New York University demonstrated an ability to make new materials with empty space on the inside, which could potentially control desired and unwanted chemical reactions.

Mike Ward, of NYU's Department of Chemistry and a team of researchers, essentially created a "molecular flask," self-assembling cages capable of housing other compounds inside of them. These "flasks" may eventually allow researchers to isolate certain chemical reactions within or outside the cage.

The research is published in the July 22, 2011 issue of the journal Science.

"We wanted to create frameworks to serve as the 'hotel' for 'guest' molecules, which can deliver the function independent of framework design," said Ward. "This makes it possible to separate chemicals based on size or perform reactions inside well-defined cages, which could potentially give you more control over chemical reactivity and reaction products. Moreover, these frameworks may prove ideal for encapsulating a wide range of guest molecules, producing materials with new optical or magnetic properties."

The molecular "hotels" described by Ward and his collaborators take the shape of a truncated octahedron, one of 13 shapes described as an Archimedean solid, discovered by the Greek mathematician Archimedes. Archimedean solids are characterized by a specific number of sides that meet at corners which are all identical. The regularity of these shapes often means they are of particular interest to chemists and materials researchers looking to create complex materials that assemble themselves.

The extraordinary aspect of this work, supported by the National Science Foundation (NSF), is the self-assembly of the molecular tiles into a polyhedron, a well-defined, three-dimensional, geometric solid. The individual polyhedra assemble themselves using the attractive interactions associated with hydrogen bonds. They then further organize into a crystal lattice that resembles a porous structure called zeolite, an absorbent material with many industrial uses.

The new material differs from zeolite because it is constructed from organic building blocks rather than inorganic ones, which make it more versatile and easier to engineer. In general, inorganic compounds are considered mineral in origin, while organic compounds are considered biological in origin.