The [Al(NH3)n]+ ions with n = 1–5 are studied by infrared photodissociation spectroscopy and density functional theory calculations. The inserted [H–Al–NH2]+ structure is calculated to be higher in energy than the adduct [Al–NH3]+ structure. However, incremental solvation stabilizes the inserted structure more efficiently than the adduct structure, because of a larger effective charge on the Al atom in [H–Al–NH2]+. Actually, the infrared spectra demonstrate that the [(H–Al–NH2)(NH3)n–1]+ ions are predominant over [Al–(NH3)n]+ for n ≥ 4, while the adduct structures dominate the spectra of [Al(NH3)n・Ar]+ for n = 1–3.

This work was supported in part by the Joint Studies Program (2004) of the Institute for Molecular Science and the Grant-in-Aid for Scientific Research (No. 17550014) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.

This is a postprint of an article published by Elsevier B.V. in Chemical Physics Letters, 2006, available online: http://doi.org/10.1016/j.cplett.2005.11.077