Unconventional ionic hydrogen bonds: CH+⋯π (CC) binding energies and structures of benzene+(acetylene)1–4 clusters

Rapid condensation of acetylene onto the benzene cation with the addition of up to eight acetylene molecules is observed in the gas phase at 120–140 K forming the C6D6+(C2H2)n clusters. The binding energies and entropy changes of the stepwise condensation of the first four acetylene molecules onto the benzene cation have been measured and correlated with the calculated lowest energy isomers. The measured binding energies (3–4 kcal/mol) reflect weak charge-induced dipole and (benzene) CHδ+⋯π CC (acetylene) hydrogen bonding interactions. Associative charge transfer is suggested to activate the cyclization of three acetylene molecules to form a benzene molecule (C6H6).