Chemists make antiaromatic nanocage

Abstract

What Jonathan Nitschke of the University of Cambridge and colleagues made shouldn’t be stable. But it is. After 2 years of work by postdoc Masahiro Yamashina, now at the Tokyo Institute of Technology, the team reports a nanosized cage with antiaromatic walls that boasts some peculiar magnetic properties (Nature 2019, DOI: 10.1038/s41586-019-1661-x). To understand why this nanocage’s stability is surprising, you have to remember Huckel’s rule. According to the rule, a molecule is aromatic if it has 4n + 2 π electrons in a system of rings containing conjugated double bonds. That aromaticity increases the stability of the compound. But when a cyclic conjugated compound has 4n π electrons, it is antiaromatic. These molecules are typically unstable and reactive, and the rings have a paramagnetic ring current that can be seen with nuclear magnetic resonance spectroscopy. To build the nanocage, Yamashina used some relatively stable antiaromatic nickel(II) norcorrole building blocks