Infrared photodissociation spectroscopy of [Al(NH3)n]+ (n = 1–5): Solvation structures and insertion reactions of Al+ into NH3

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.