Synthesis of Calix[4]arene-Based Porous Organic Cages and Their Gas Adsorption

Two crystalline large-sized porous organic cages (POCs) based on conical calix[4]arene (C4A) were designed and synthesized. The four-jaw C4A unit tends to follow the face-directed self-assembly law with the planar triangular building blocks such as tris(4-aminophenyl)amine (TAPA) or 1,3,5-tris(4-aminophenyl)benzene (TAPB) to generate a predictable cage with a stoichiometry of [6+8]. The formation of the large cages is confirmed through their relative molecular mass measured using MALDI-TOF/TOF spectra. The protonated molecular ion peaks of C4A-TAPA and C4A-TAPB were observed at m/z 5109.0 (calculated for C₃₃₆H₂₄₀O₂₄N₃₂: m/z 5109.7) and m/z 5594.2 (calculated for C₃₈₄H₂₆₄O₂₄N₂₄: m/z 5598.4). C4A-POCs exhibit I-type N₂ adsorption-desorption isotherms with the BET surface areas of 1444.9 m² ⋅ g^-1 and 1014.6 m² ⋅ g^-1. The CO₂ uptakes at 273 K are 62.1 cm³ ⋅ g^-1 and 52.4 cm³ ⋅ g^-1 at a pressure of 100 KPa. The saturated iodine vapor static uptakes at 348 K are 3.9 g ⋅ g^-1 and 3.5 g ⋅ g^-1. The adsorption capacity of C4A-TAPA for SO₂ reaches to 124.4 cm³ ⋅ g^-1 at 298 K and 1.3 bar. Additionally, the adsorption capacities of C4A-TAPA for C₂H₂, C₂H₄, and C₂H₆ were evaluated.