In the search for ditriel B⋯Al non-covalent bonding†
The ditriel B⋯Al interaction has been characterised in Fδ−Bδ+⋯Alδ+Fδ− (δ > 0.6e) molecules using CCSD(T)/aug-cc-pVTZ calculations. It has a non-covalent character as evidenced by the topological analysis of electron density (AIM) and electron localisation function (ELF). The B⋯Al bonding is very weak (<1 kcal mol−1) and unique among the FBTF (T = B, Al, Ga, In) molecules. SAPT analysis shows that it has mainly an electrostatic character but the energetic stability of the molecule is gained at the second order of the perturbation expansion with the dispersion and induction energies. Substitution of the F atom by less electronegative atoms such as Cl, Br, I and At results in the shortening of the B⋯Al separation and creating XBAlX (X = Cl, Br, I, At) molecules with 2c–2e covalent B–Al bonds. The topology of ELF for BF and AlF bonds reveals features, which may be explained evoking the high electropositive character of the Al atom.