On the remarkable resistance to oxidation by the Bi18− cluster | Science Advances

The reactivity of Bi _n ⁻ clusters ( n = 2 to 30) with O ₂ is found to display even-odd alternations. The open-shell even-sized Bi _n ⁻ clusters are more reactive than the closed-shell odd-sized clusters, except Bi ₁₈ ⁻ , which exhibits no observable reactivity toward O ₂ . We have investigated the structure and bonding of Bi ₁₈ ⁻ to understand its remarkable resistance to oxidation. We find that the most stable structure of Bi ₁₈ ⁻ consists of two Bi ₈ cages linked by a Bi ₂ dimer, where each atom is bonded to three neighboring atoms. Chemical bonding analyses reveal that each Bi uses its three 6 p electrons to form three covalent bonds with its neighbors, resulting in a Bi ₁₈ ⁻ cluster without any dangling bonds. We find that the robust Bi ₁₈ framework along with the totally delocalized unpaired electron is responsible for the surprising inertness of Bi ₁₈ ⁻ toward O ₂ . The Bi ₁₈ framework is similar to that in Hittorf’s phosphorus, suggesting the possibility to create bismuth nanoclusters with interesting structures and properties.