A Robust Molecular Porous Material for C2H2/CO2 Separation

A molecular porous material, MPM-2, comprised of cationic [Ni-2(AlF6)(pzH)(8)(H2O)(2)] and anionic [Ni2Al2F11(pzH)(8)(H2O)(2)] complexes that generate a charge-assisted hydrogen-bonded network with pcu topology is reported. The packing in MPM-2 is sustained by multiple interionic hydrogen bonding interactions that afford ultramicroporous channels between dense layers of anionic units. MPM-2 is found to exhibit excellent stability in water (>1 year). Unlike most hydrogen-bonded organic frameworks which typically show poor stability in organic solvents, MPM-2 exhibited excellent stability with respect to various organic solvents for at least two days. MPM-2 is found to be permanently porous with gas sorption isotherms at 298 K revealing a strong affinity for C2H2 over CO2 thanks to a high (Delta Q(st))(AC) [Q(st) (C2H2) - Q(st) (CO2)] of 13.7 kJ mol(-1) at low coverage. Dynamic column breakthrough experiments on MPM-2 demonstrated the separation of C2H2 from a 1:1 C2H2/CO2 mixture at 298 K with effluent CO2 purity of 99.995% and C2H2 purity of >95% after temperature-programmed desorption. C-H center dot center dot center dot F interactions between C2H2 molecules and F atoms of AlF63- are found to enable high selectivity toward C2H2, as determined by density functional theory simulations.

Automated summary

A molecular porous material, MPM-2, comprised of cationic [Ni-2(AlF6)(pzH)(8)(H2O)(2)] and anionic [Ni2Al2F11(pzH)(8)(H2O)(2)] complexes that generate a charge-assisted hydrogen-bonded network with pcu topology is reported. MPM-2 exhibits excellent stability in both water and organic solvents. It shows high selectivity for C2H2 over CO2 and can effectively separate C2H2 from a mixture.