Strange new bonds found hiding in plain sight in common organometallics

A new bond type called collective bonding has been discovered in well-known boron, aluminium, organolithium and organomagnesium compounds. In these molecules, there is little bonding between the central neighbouring atoms – their stability can only be explained by global interactions.

When chemists first made NaBH₃^– from the common reducing agent sodium borohydride, they immediately realised it had a rather unusual bond. They proposed a dative bond between Na⁻ and BH₃. Other researchers disagreed, suggesting an electron-sharing covalent bond instead.