Trapping N2 and CO2 on the Sub-Nano Scale in the Confined Internal Spaces of Open-Cage C60 Derivatives: Isolation and Structural Characterization of the Host-Guest Complexes

An open-cage C60 tetraketone with a large opening was able to encapsulate N2 and CO2 molecules after its exposure to high pressures of N2 and CO2 gas. A subsequent selective reduction of one of the four carbonyl groups on the rim of the opening induced a contraction of the opening (→2) and trapped the guest molecules inside 2. The thus-obtained host-guest complexes N2@2 and CO2@2 could be isolated by recycling HPLC, and were found to be stable at room temperature. The molecular structures of N2@2 and CO2@2 were determined by single-crystal X-ray diffraction analyses, and revealed a short N≡N triple bond for the encapsulated N2, as well as an unsymmetric molecular structure for the encapsulated molecule of CO2. The IR spectrum of CO2@2 suggested that the rotation of the encapsulated molecule of CO2 is partially restricted, which was supported by DFT calculations.