Formation and properties of halogenated aluminum clusters

The fast-flow tube reaction apparatus was employed to study the halogenation of aluminum clusters. For reactions with HX (X=Cl, Br, and I), acid-etching pathways are evident, and we present findings for several reactions, whereby AlnX- generation is energetically favorable. Tandem reaction experiments allowed us to establish that for AlnCl-, AlnI-, and AlnI2-, species with n=6, 7, and 15 are particularly resistant to attack by oxygen. Further, trends in reactivity suggest that, in general, iodine incorporation leaves the aluminum clusters' electronic properties largely unperturbed. Ab initio calculations were performed to better interpret reaction mechanisms and elucidate the characteristics of the products. Lowest energy structures for Al13X- were found to feature icosahedral Al-13 units with the halogen atom located at the on-top site. The charge density of the highest occupied molecular orbital in these clusters is heavily dependent on the identity of X. The dependence of reactivity on the clusters' charge state is also discussed. In addition, we address the enhanced stability of Al13I- and Al13I2-, arguing that the superhalogen behavior of Al-13 in these clusters can provide unique opportunities for the synthesis of novel materials with saltlike structures. (C) 2004 American Institute of Physics.