Assembly of HCN hydrogen bonding chains in the gas phase. Binding energies and structures of phenylacetylene+(HCN)n clusters, n = 1–4

The stepwise binding energies (ΔHon−1,n) of 1–4 HCN molecules to the phenylacetylene radical cation (C8H6+) are determined by equilibrium thermochemical measurements. The binding energy (10.5 ± 1 kcal/mol) of the C8H6+ (HCN) complex is dominated by the ionic hydrogen bonding interaction (ph-CCHδ+⋯NCH). For higher clusters, the attachment of HCN molecules occurs through two comparable interactions involving the association of HCN molecules (ph-CCHδ+⋯NCH⋯NCH⋯) to form a linear hydrogen bonding chain or the interaction with the ring hydrogen atoms through hydrogen bonding (>CHδ+⋯NCH) and bifurcated charge-dipole structures. An interesting pattern of the assembly of linear hydrogen bonded chains is observed and could result in the formation of molecular wires of nanometer length scale.