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-N-H-3](+) 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) center dot Ar](+) for n = 1-3. (c) 2005 Published by Elsevier B.V.