Preferential Adsorption of CO₂ in an Ultramicroporous MOF with Cavities Lined by Basic Groups and Open-Metal Sites

Here, we present a new ultramicroporous Cu₂ paddlewheel based MOF. This ultramicroporous MOF has most of the features such as porosity (BET surface area = 945 m²/g), CO₂ capacity (3.5 mmol/g at ambient temperature and pressure), CO₂/N₂ selectivity (sCO₂/N₂ = 250), and fast CO₂ diffusion kinetics ( D_c = 2.25 × 10^-9 m²/s), comparable to some of the other high-performing ultramicroporous MOFs, with strong binding sites. Typically, such MOFs exhibit strong CO₂-framework interactions (evidenced from a heat of adsorption ≥ 38 kJ/mol). However, the MOF explained here, despite having channels lined by the amine and the open-metal sites, possesses only a moderate CO₂-framework interaction (HOA = 26 kJ/mol). Using periodic DFT, we have probed this counterintuitive observation.