UC San Diego

The reactivity of Bin- clusters (n = 2 to 30) with O2 is found to display even-odd alternations. The open-shell even-sized Bin- clusters are more reactive than the closed-shell odd-sized clusters, except Bi18-, which exhibits no observable reactivity toward O2. We have investigated the structure and bonding of Bi18- to understand its remarkable resistance to oxidation. We find that the most stable structure of Bi18- consists of two Bi8 cages linked by a Bi2 dimer, where each atom is bonded to three neighboring atoms. Chemical bonding analyses reveal that each Bi uses its three 6p electrons to form three covalent bonds with its neighbors, resulting in a Bi18- cluster without any dangling bonds. We find that the robust Bi18 framework along with the totally delocalized unpaired electron is responsible for the surprising inertness of Bi18- toward O2. The Bi18 framework is similar to that in Hittorfs phosphorus, suggesting the possibility to create bismuth nanoclusters with interesting structures and properties.