A microporous Co2+ metal organic framework with single-crystal to single-crystal transformation properties and high CO2 uptake

The synthesis and characterization of {[Co9(INA)18(H2O)6]·11DMF·15H2O}∞ (Co9-INA·11DMF·15H2O) (INA- = the anion of isonicotinic acid) is reported. It exhibits a rigid 3D-porous structure with a Co9 repeating unit consisting of four [CoII2(μ-O2CR)2(μ-H2O)] subunits (two unique) linked through bridging INA- ligands to an isolated CoII ion (half unique). The [CoII2] dimers and the isolated CoII ion have assembled to create a trinodal (6,7,8)-coordinated network with point symbol (32.411.56.62)2(32.418.54.64)2(34.44.54.63). Gas sorption studies revealed that Co9-INA exhibits 910 m2 g-1 BET area, 4.2 mmol g-1 CO2 uptake at 273 K/1 bar, and 6.7 CO2/CH4 selectivity at zero coverage. Furthermore, Co9-INA displays capability for exchange of the guest solvent molecules by various organic molecules in a single-crystal to single-crystal fashion. Direct and alternating current magnetic susceptibility studies revealed the existence of dominant antiferromagnetic interactions between the Co2+ ions that result in a paramagnetic ST = 3/2 spin ground state value. Overall, this work emphasizes the potential of relatively simple and inexpensive polytopic ligands, such as isonicotic acid, to stabilize microporous MOFs with significant CO2 sorption capacity.