The HKrCCH⋯CO2 complex: an ab initio and matrix-isolation study

Abstract

We report an experimental and theoretical study on new noble-gas hydride complex HKrCCH⋯CO₂, which is the first known complex of a krypton hydride with carbon dioxide. This species was prepared by the annealing-induced H + Kr + CCH⋯CO₂ reaction in a krypton matrix, the CCH⋯CO₂ complexes being produced by UV photolysis of propiolic acid (HCCCOOH). The H–Kr stretching mode of the HKrCCH⋯CO₂ complex at 1316 cm⁻¹ is blue-shifted by 74 cm⁻¹ from the most intense H–Kr stretching band of HKrCCH monomer. The observed blue shift indicates the stabilization of the H–Kr bond upon complexation, which is characteristic of complexes of noble-gas hydrides. This spectral shift is slightly larger than that of the HKrCCH⋯C₂H₂ complex (+60 cm⁻¹) and significantly larger than that of the HXeCCH⋯CO₂ complex (+32 and +6 cm⁻¹). On the basis of comparison with ab initio computations at the MP2 and CCSD(T) levels of theory, the experimentally observed absorption is assigned to the quasi-parallel configuration of the HKrCCH⋯CO₂ complex. The calculated complexation-induced spectral shift of the H–Kr stretching band (60.4 or 72.7 cm⁻¹ from the harmonic calculations at the MP2 and CCSD(T) levels, respectively) agrees well with the experimental value.