Triple-bonded boron opens new chemical world: It turns out that to coax boron atoms to form triple bonds at room temperature, Braunschweig and colleagues had to make sure all the spaces where it could hold outer electrons were occupied.
Boron has four outer slots that can hold up to two electrons each – but in atomic boron, one of these slots is completely empty and the other three are only half full, with one electron apiece.
First the team filled up the completely empty slot by bonding each boron atom with a carbon-and-nitrogen-containing molecule called an N-heterocyclic carbene, which donated two electrons. Boron atoms bound to the molecule then completed the filling of their slots by pairing up and pooling their original three electrons. Each boron atom then has a full outer suite of eight electrons (see diagram, above right).
As long as it is not exposed to air or moisture, with which it is known to react, the resulting green crystal with the rare triple bond should stay stable indefinitely, Braunschweig says.