Reactions of Alnlx- with methyl iodide:: The enhanced stability of Al7l and the chemical significance of active centers

AI(n)I(x)(-) are reacted with methyl iodide, and the reaction mechanisms and products are discussed. The relevance of previous studies of the reactions between bare aluminum clusters and methyl iodide is addressed, and the chemical differences reported herein are explained. Particular attention is given to parallels with the known chemistry of alkyl halides on aluminum surfaces, where kinetically mediated etching reactions are prominent. The emergence of AI(7)I(-) as the dominant product in the present reactions is addressed via electronic structure calculations, which reveal that the cluster can be described in terms of an electron bound to a "jellium compound". Other significant products of the etching reaction include I-, I-3(-), and, importantly, the polyhalide-like AI(13)I(2x)(-) clusters. In the AI(13)I(x)(-) series, clusters with odd values for x are found to be reactive, and those with even x are far more stable. This observation is explained in terms of the presence or absence of active sites.