Structures of [Mg · (H2O)1,2]+ and [Al · (H2O)1,2]+ ions studied by infrared photodissociation spectroscopy: evidence of [HO–Al–H]+ ion core structure in [Al · (H2O)2]+

Infrared spectra of [Mg · (H2O)1,2]+ and [Al · (H2O)1,2]+ are measured in the OH stretching region (3200–3800 cm−1). The spectra show the symmetric and asymmetric OH stretching bands of water molecules that are directly bound to the metal ions through metal–oxygen intermolecular bonds. In addition to these bands, the [Al · (H2O)2]+ ion has another band at 3714 cm−1. This band is assigned to the free OH stretching vibration of the [HO–Al–H]+ ion; the aluminum ion is inserted into the O–H bond of one water molecule in [Al · (H2O)2]+.