H−π Complexes of Acetylene−Ethylene:  A Matrix Isolation and Computational Study

Abstract

Hydrogen-bonded H···π complexes of C 2 H 2 and C 2 H 4 were studied both computationally and experimentally. Computationally, C 2 H 2 - C 2 H 4 clusters ranging from 1:1 to 6:1 stoichiometries were identified. Using matrix isolation infrared spectroscopy, the 1:1 adduct was studied in an argon matrix. Formation of these adducts was evidenced by shifts in the vibrational frequencies of the acetylene and ethylene submolecules in the complex. The molecular structure, vibrational frequencies, and stabilization energies of the complexes were calculated at the HF, MP2, MP2(full), and B3LYP levels of theory by employing basis sets ranging from 6-31G(d,p) to 6-311++G(2d,2p). Both computations and experiments showed that two types of complexes are formed, one in which acetylene acts as a proton donor to the π cloud of ethylene and another in which ethylene acts as the proton donor to the π cloud of acetylene. Structures, interaction energies, and vibrational frequencies have also been obtained for 1:2, 1:4, and 1:6 complexes of ethylene and acetylene. This work presents a case study of hydrogen-bonded clusters formed through the H−π interaction.