Chemists discover first new chemical bond in more than a decade

Chemists rarely create new kinds of chemical bonds, but they’ve done it: covalent bonds that depend on a single electron came about almost a century after they were first proposed.

Takuya Shimajiri and his colleagues at the University of Tokyo have been testing the limits of chemical bonds for years, experimenting with unusually long and flexible bonds, but now they’re tackling an idea first proposed by chemist Linus Pauling in 1931: a chemical bond formed by just a single electron.

All known covalent bonds, in which atoms bond by sharing electrons, involve two, four, six, or eight electrons, but Pauling theorized that a covalent bond might exist in which two atoms share one electron. To achieve this, the researchers used a chemical reaction to remove an electron from an existing two-electron covalent bond between two carbon atoms. They used large hydrocarbons, in which the bonds between the carbon atoms are very long, meaning that it would be energetically costly for an electron elsewhere in the molecule to replace the one removed.

Shimajiri says previous experiments that attempted this kind of electron subtraction left behind weak bonds that broke too quickly for conclusive chemical analysis. But his team’s molecule was stable enough that they could analyze it with X-rays and several kinds of light. Based on how this radiation bounced off and was absorbed, the team determined that it had a stable, one-electron bond.

“It’s not often that you find a molecule with a new kind of bond,” says Henry Rzepa of Imperial College London. He says that the molecule had a total of 278 electrons, so removing one of the right electrons and preventing others from quickly replacing it was a huge feat. Rzepa says this is a “major discovery” that could inspire chemists to create an entirely new family of molecules.

Chemists can now study how one-electron covalent bonds change chemical reactions, Shimajiri says, but he and his colleagues also have bigger questions.

“We’re trying to determine what covalent bonds are and, specifically, at what point a bond is considered covalent and at what point it’s not. Our goal is to explore a wide range of bonds that have yet to be discovered,” he says.