A pcu topology metal-organic framework, Ni(1,4-bib)(inca)₂, that exhibits high CO₂/N₂ selectivity and low water vapour affinity

Herein we report the synthesis of a new metal-organic framework, Ni(1,4-bib)(inca)₂ or pcu-1-Ni, where 1,4-bib = 1,4-bis(imidazole-1-yl)benzene, inca = indazole-5-carboxylic acid, through the crystal engineering strategy of using an N-donor linker to pillar a square lattice, sql, topology net. pcu-1-Ni adopts pcu topology and features two types of hydrophobic pore, small pore A and large pore B. The biporous nature of pcu-1-Ni is reflected in its stepped CO₂ and H₂O adsorption isotherms, highlighting the influence of pore size and chemistry on gas and water vapour sorption properties. pcu-1-Ni exhibits the unusual combination of high CO₂/N₂ selectivity (IAST selectivity 100-250) and low water affinity at low RH (an S-shaped water vapour isotherm with an inflection point at 45-65% RH). Whereas pcu-1-Ni degrades upon repeated exposures to water vapour, its structure-property relationships can provide guidance for design of the next generation of CO₂-selective sorbents. In this context, Canonical Monte Carlo simulations provide insight into the preferential adsorption of CO₂ over N₂ and H₂O.