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

The unique bifunctional porous metal-organic framework, [Co(HLdc)]center dot 1.5MeOH center dot 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.