Divergent Kinetic and Thermodynamic Hydration of a Porous Cu(II) Coordination Polymer with Exclusive CO2 Sorption Selectivity

Selective adsorption and separation of CO2 are of great importance for different target applications. Metal–​organic frameworks (MOFs) represent a promising class of porous materials for this purpose. Here we present a unique MOF material, [Cu­(tba)2]n (tba = 4-(1H-1,2,4-triazol-1-yl)­benzoate), which shows high CO2 adsorption selectivity over CH4/​H2/​O2/​Ar/​N2 gases (with IAST selectivity of 41–68 at 273 K and 33–51 at 293 K). By using a critical point dryer, the CO2 molecules can be well sealed in the 1D channels of [Cu­(tba)2]n to allow a single-crystal X-ray analysis, which reveals the presence of not only Cδ+H···Oδ− bonds between the host framework and CO2 but also quadrupole–​quadrupole (CO2δ−···δ+CO2) interactions between the CO2 molecules. Furthermore, [Cu­(tba)2]n will suffer divergent kinetic and thermodynamic hydration processes to form its isostructural hydrate {[Cu­(tba)2]­(H2O)}n and a mononuclear complex [Cu­(tba)2(H2O)4] via single-crystal to single-crystal transformations.