On the remarkable resistance to oxidation by the Bi 18 − cluster

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.