A matrix isolation and ab initio study of the hydrogen bonded complexes of acetylene with pyridine

Hydrogen bonded complexes of acetylene and pyridine were studied using matrix isolation spectroscopy and ab initio computations. The adduct was formed by depositing acetylene and pyridine in an argon matrix and a 1:1 C2H2-NC5H5 complex was identified using infrared spectroscopy. Formation of the adduct was evidenced from the shifts in the vibrational frequencies of C2H2 in the complex compared with that of free C2H2. The molecular structure, vibrational frequencies and stabilization energies of the complex were computed at the HF/6-31++G** and B3LYP/6-31++G** levels. We located one minimum on the potential surface, corresponding to a strongly bound C2H2-NC5H5 n-σ complex. Both experimental and computational data indicated that C2H2 acts as a proton donor and C5H5N as a proton acceptor.