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 C(δ+)-H···O(δ-) bonds between the host framework and CO2 but also quadrupole-quadrupole (CO2(δ-)···(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.