Unlikely ion made in lab

From Orlando, Fla., at a meeting of the American Chemical Society

In a surprising discovery, chemists have created a molecule that many researchers thought was too unstable to exist long enough to be identified or studied. The positively charged ion, called the pentamethylcyclopentadienyl cation, lasts for weeks at room temperature and is so stable that it can sit in open air on a laboratory bench top without decomposing, report Lijun Lin of Northwestern University in Evanston, Ill., and her colleagues.

The researchers accidentally produced the allegedly unstable cation, in the form of a crystalline salt, while trying to make another type of cation, says Lin’s colleague Joseph Lambert of Northwestern. The researchers then developed a simple process for making the cation in a more direct way and determined the substance’s structure using X-ray crystallography.

In general, cyclopentadienyl cations have been regarded as unstable because of their electronic structure. They’re classified as antiaromatic molecules, which chemical theory predicts will be extremely reactive–in contrast to aromatics, such as benzene, which have unusually stable structures.

The team is now exploring the chemistry this once unlikely cation can do. Lin, Lambert, and Vitaly Rassolov of the University of South Carolina in Columbia also report their finding in the April 15 Angewandte Chemie International Edition.

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