A Robust Molecular Porous Material for C 2 H 2 /CO 2 Separation.

A molecular porous material, MPM-2, comprised of cationic [Ni 2 (AlF 6 )(pzH) 8 (H 2 O) 2 ] and anionic [Ni 2 Al 2 F 11 (pzH) 8 (H 2 O) 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 C 2 H 2 over CO 2 thanks to a high (ΔQ st ) AC [Q st (C 2 H 2 ) - Q st (CO 2 )] of 13.7 kJ mol -1 at low coverage. Dynamic column breakthrough experiments on MPM-2 demonstrated the separation of C 2 H 2 from a 1:1 C 2 H 2 /CO 2 mixture at 298 K with effluent CO 2 purity of 99.995% and C 2 H 2 purity of >95% after temperature-programmed desorption. C-H···F interactions between C 2 H 2 molecules and F atoms of AlF 6 3- are found to enable high selectivity toward C 2 H 2 , as determined by density functional theory simulations.