On the Al + HCN reaction in helium nanodroplets

The sequential addition of HCN and Al to a helium nanodroplet leads barrierlessly to a bent, planar, 2A′, HCNAl species, which is computed to be 20.3 kcal/mol below the separated reactants. A ro-vibrational band near 2690 cm−1 is assigned to the ν1 (a′) CH stretch. A Natural Bond Orbital analysis of this reaction product reveals that both ligand-to-metal σ-donation and metal-to-ligand π-donation are responsible for the strong bonding between HCN and Al. A significant donor–acceptor interaction between the C–N and C–H anti-bonding orbitals is responsible for the bent geometry and the 619 cm−1 red shift of the CH stretch band upon complexation.