Complexes of carbon dioxide with dihalogenated ethylenes: structure, stability and interaction

Abstract

Interactions of ethylene and its 1,2-dihalogenated derivatives with CO₂ induce the formation of twenty four molecular complexes with stabilization energies in the range of 1.1 to 7.5 kJ mol⁻¹ as computed at the CCSD(T)/aug-cc-pVTZ//MP2/aug-cc-pVDZ level. The stability of the parent C₂H₄⋯CO₂ complex is due to a π⋯π* interaction which has not yet been reported in the complexes of CO₂-philic compounds and CO₂. The cis-XCHCHX⋯CO₂ complexes are found to be slightly more stable than the trans-XCHCHX⋯CO₂, with X = F, Cl and Br. Generally, the overall stabilization energy of each complex is determined by the C–H⋯O hydrogen bond and the C–X⋯C Lewis acid–base interaction, in which the latter plays a larger role. Substitution of two H atoms in CH₂CH₂ by the same halogen atoms stabilizes the complexes XCHCHX⋯CO₂, and for the same dihalogenated derivatives, the stability of XCHCHX⋯CO₂ tends to increase from X = F via Cl and to Br. The obtained results suggest that the contraction of the C–H bond involved in the C–H⋯O hydrogen bond and the blue-shift of its stretching frequency depend not only on a polarization of the C–H bond in the isolated monomer but also on the geometric shape of the complex formed.