This Research award in the Inorganic, Bioinorganic and Organometallic Chemistry program supports work by Professors Robert D. Pike at the College of William and Mary and Craig A. Bayse at Old Dominion University to carry out structural, reactivity and computational studies on metal-organic networks which can act as luminescence detectors and chemical catalysts. Metal-organic networks are large molecules in which metal atoms (e.g. copper) are linked together to form long-range lattices, which may be one- two- or three-dimensional in structure. The metals in these materials have the ability to bind small molecules, including gases. In the case of copper in the +1 oxidation state, this binding changes the fluorescence color emitted by the copper ions. As a result, metal-organic networks containing copper can potentially act as sniffing devices for environmental chemicals. In addition, this same type of molecular binding may enable efficient and environmentally benign catalytic reactions of small molecules to be carried out using flow-through reactors charged with metal-organic network catalysts. The research is being conducted entirely by undergraduate chemistry students. These students, who are being trained at the interface of chemistry, materials science and photophysics, are part of the next generation of U.S. scientists and will serve as teachers for the Crystals program, aimed at enhancing interest in the sciences at the elementary school level. The Crystals program utilizes hands-on experiments to demonstrate for fifth grade students how the physical properties and mathematical symmetry of beautiful crystals reflect the underlying chemical structure. The research is ultimately intended to produce better detectors for chemical pollutants and/or weapons agents and to give rise to more environmentally-friendly catalysts for chemical synthesis.
Investigations were carried out in hopes of identifying a copper-based detector material for volatile organic compounds (VOCs). VOCs are emitted by many chemical processes and consumer products. They represent to threat to human health in enclosed spaces. The goal of the project was to find a material that would change its fluorescent behavior under black light when it comes into contact with certain VOCs. Copper compounds, in particular copper iodide, were found to be very promising for this application. Copper iodide does not fluoresce in the visible region under black light, but does so when exposed to many nitrogen- and sulfur-containing VOCs. A fiber-optic LED flowing-gas instrument was built to investigate the relationship between amount of VOC and detector response. Our finding showed that exposure of copper iodide to VOCs produces strong emission (see figure). Unfortunately, sufficiently low levels of VOCs needed to make such a detector commercially viable were not found. During the study, a variety of new modes of metal-organic networking behavior were identified. Moreover, the study uncovered additional information concerning the nature of absorption and emission of light by copper compounds. In addition to studying the nature of copper iodide adducts of VOCs, the adducts of copper cyanide and copper thiocyanate were also studied. As with copper iodide, a remarkable variety of structural types was uncovered. The compounds were generally fluorescent, although not as strongly as those of copper iodide, making them less likely to serve as VOC detector materials. During the course of the project ten undergraduate students and one Masters student from the College of William & Mary participated. Many of these students participated in outreach activities to local fifth grade classes. This program called "Crystals!" taught the fifth grade students about the nature of crystals and gave them hands-on experience in growing their own crystals and examining them under magnification. Of the eleven William and Mary students involved in the project, nine have now graduated: four are in chemistry graduate programs, one is in medical school, one is in pharmacy school, two are working in the chemistry industry.
