Selective CO₂ uptake and inverse CO₂/C₂H₂ selectivity in a dynamic bifunctional metal–organic framework

The unique bifunctional porous metal–organic framework, [Co(HL^dc)]·1.5MeOH·dioxane, incorporates both free-standing carboxyl and pyridyl groups within its pores. Gas adsorption measurements on the desolvated framework reveal unusual selective CO₂ adsorption over C₂H₂ and CH₄ linked to a framework phase change from a narrow pore (np) to a large pore (lp) form, mediated by CO₂ uptake at 195 K. This phase transition has been monitored by in situ powder X-ray diffraction and IR spectroscopy, and modelled by Grand Canonical Monte Carlo simulations revealing that the reversible np to lp transition is linked to the rotation of pyridyl rings acting as flexible “pore gates”.