Matrix-isolation and computational study of the HKrCCH⋯HCCH complex†
The HKrCCH⋯HCCH complex is identified in a Kr matrix with the H–Kr stretching bands at 1316.5 and 1305 cm−1. The monomer-to-complex shift of the H–Kr stretching mode is about +60 cm−1, which is significantly larger than that reported previously for the HXeCCH⋯HCCH complex in a Xe matrix (about +25 cm−1). The HKrCCH⋯HCCH complex in a Kr matrix is formed at ∼40 K via the attachment of mobile acetylene molecules to the HKrCCH monomers formed at somewhat lower annealing temperatures upon thermally-induced mobility of H atoms (∼30 K). The same mechanism was previously proposed for the formation of the HXeCCH⋯HCCH complex in a Xe matrix. The assignment of the HKrCCH⋯HCCH complex is fully supported by the quantum chemical calculations. The experimental shift of the H–Kr stretching mode is comparable with the computational predictions (+46.6, +66.0, and +83.2 cm−1 at the B3LYP, MP2, and CCSD(T) levels of theory, respectively), which are also bigger that the calculated shift in the HXeCCH⋯HCCH complex. These results confirm that the complexation effect is bigger for less stable noble-gas hydrides.