All-metal aromatic ring isolated for the first time

A four-atom bismuth species is the first all-metal ring with aromatic bonding character to have been isolated in the lab. The structure was synthesised by researchers in Germany, who say that their findings raise important questions around the nature of aromaticity in materials composed of heavier elements.

Despite having been studied for almost 200 years, aromaticity remains one of chemistry’s most enigmatic phenomena. At school, almost every student will learn about aromatic carbon rings like benzene, but attempts to make analogous compounds entirely from metal atoms have proven much more difficult. In 2001, the aromatic all-metal species Al₄^2˗ was detected spectroscopically, while the antiaromatic Al₄^4˗ was detected in 2003. However, the only aromatic metal rings – including gallium, gold and thorium species – to have been isolated in the lab have needed to be stabilised by covalently bonded non-metal substituents.