On the remarkable resistance to oxidation by the Bi₁₈^- cluster.

Abstract

The reactivity of Bi<i>_n</i>^- clusters (<i>n</i> = 2 to 30) with O₂ is found to display even-odd alternations. The open-shell even-sized Bi<i>_n</i>^- 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 6<i>p</i> 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 Hittorf's phosphorus, suggesting the possibility to create bismuth nanoclusters with interesting structures and properties.