Diatomic molecule aluminum monochloride (AlCl) was discovered by Cernicharo & Guélin in 1987 toward the carbon star IRC +10216, a noted molecule factory. The detection was based on four non-consectutive rotational lines. It has not been confirmed some 30 years later.

The diatomic forms of salts like AlCl are completely unstable under normal terrestrial conditions. The salt (bulk AlCl₃) is used as a catalyst in Friedel-Crafts reactions.

A variety of other diatomic and triatomic aluminum compounds have been detected in space, including aluminum monofluoride, AlF, aluminum isocyanide, AlNC, aluminum monoxide, AlO, and aluminum monohydroxide, AlOH.