A Robust Molecular Porous Material for C₂H₂/CO₂ Separation

Abstract 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 (ΔQ_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···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.