Dihydrogen intermolecular contacts in group 13 compounds: HH or EH (E = B, Al, Ga) interactions?

A systematic theoretical analysis of homopolar dihydrogen interactions in group 13 compounds is presented here. Ab initio calculations and structural analysis allow us to demonstrate that interactions involving B-HH-B contacts are comparable in strength to the previously studied C-HH-C ones, yet attractive and important for the stabilization of dimers of large molecules. We have also shown that a polyhedral skeleton enhances the B-HH-B interaction strength with respect to non-polyhedral compounds, and it has also been proven that Al-HH-Al and Ga-HH-Ga interactions can be attractive in some cases. If HE (B, Al and Ga) short contacts are present, the interaction is significantly strengthened, especially for Al and Ga. In general, HH interactions combined with associated HE (B, Al and Ga) short contacts are responsible for the stability of a large number of dimers of group 13 compounds and may play an important role in the packing of their crystal structures.