A Robust Molecular Porous Material for C2H2/CO2 Separation

A molecular porous material, MPM‐2, comprised of cationic [Ni2(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 (ΔQst)AC [Qst (C2H2) − Qst (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···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. MPM‐2 is the first Molecular Porous Material comprised of coordinated AlF63− and Al2F115− units. It has a strong sorption preference to C2H2 and exhibits dynamic breakthrough column separation of C2H2 from a 1:1 mixture of C2H2/CO2. Efficient C2H2 separation is enabled by a binding site offering strong electrostatic interactions between C2H2 and F‐atoms of AlF63− moieties as indicated by density functional theory (DFT).