This metal triangle seems to defy definition – is it aromatic or not?

When scientists discovered the first aromatic thorium ring last year, it seemed to defy what was known about actinide chemistry. But other researchers have now challenged this, saying that aromaticity indicators have been misinterpreted and that chemists should stop using aromaticity to describe metal clusters.

While this may seem like a purely academic discussion, knowing whether a molecule is aromatic or not is important to all chemists. ‘It’s teaching us something about the way nature is prepared to organise elements and what the consequences are,’ says Stephen Liddle from the University of Manchester, UK, who co-discovered the tri-thorium cluster.