Ellen Phiddian
Cosmos science journalist
It’s a central feature of chemistry: the covalent bond, one of the most common chemical bonds, happens when 2 atoms share pairs of electrons.
Most of the molecules that make us – from proteins, to water, to the air we breathe – are made of atoms in these pair-sharing covalent bonds.
Nearly 100 years ago, in 1931, chemistry giant Linus Pauling suggested it was possible to form a covalent bond with just one electron. Such a bond would be much weaker than the typical electron pair, but chemically feasible.
He has since been proven right with a variety of strange compounds – typically involving metals or boron – but until now, no-one has managed to bind 2 carbon atoms together with a single electron.
A team of Japanese researchers has made a molecule which features a carbon-carbon bond, sharing just 1 electron. They’ve published their discovery in Nature.
Their molecule is made from carbon and hydrogen atoms, linked in interlocking aromatic rings, and stabilised by iodine atoms.
When made in the lab, this molecule formed dark violet crystals which the researchers were able to study with X-ray diffraction and spectroscopy – shining different types of light through the substance to understand its structure.
This allowed them to confirm that two of the carbon atoms were sharing just 1 electron in a type of covalent bond called a sigma bond.
“These results thus constitute the first piece of experimental evidence for a carbon-carbon single-electron covalent bond, which can be expected to pave the way for further developments of the chemistry of this scarcely-explored type of bonding,” says lead author Takuya Shimajiri, now a chemist at the University of Tokyo.
“Elucidating the nature of single-electron sigma-bonds between two carbon atoms is essential to gain a deeper understanding of chemical-bonding theories and would provide further insights into chemical reactions,” says co-author Professor Yusuke Ishigaki, a chemist at Hokkaido University.
