Studies on anion recognition are motivated by the importance of ions in chemistry and biology. Anions like tetrafluoroborate (BF4–) have roles in ion-pairing catalysis and hexafluorophosphate (PF6–) is employed in Li-ion batteries. Some anions have deleterious effects on human health, e.g., the perchlorate anion (ClO4–) from rocket fuel that accumulates in drinking water competes with iodide during thyroid hormone biosynthesis. Yet, the design of receptors to bind these large anions (r > 2 Å) is made difficult by the fact that there are traditionally considered weakly coordinating. Research conducted in the Flood group at Indiana University Bloomington lead to the creation of a five-fold symmetric macrocycle, called cyanostar, that binds these large anions extremely strongly (~1012 M–2). This stabilization is 107 times greater than prior examples. The results were published in Nature Chemistry. Over the past four years, the Flood group has been a regular user of the micro-crystallography setup at APS’s ChemMatCARS, which was designed by Dr. Yu-Sheng Chen, from the University of Chicago. Allowing for fast measurement of ultra-small crystals and including low temperature capabilities, the setup has been vital for this study.
Semin Lee, Chun-Hsing Chen & Amar H. Flood
A pentagonal cyanostar macrocycle with cyanostilbene CH donors binds anions and forms dialkylphosphate rotaxanes
Nature Chemistry 5, 704-710 (2013). Author affiliation: Indiana University, Bloomington.